diff --git a/core/assets/scaffold/files/default.settings.php b/core/assets/scaffold/files/default.settings.php
index 1c8dbee9e7..935de3e44d 100644
--- a/core/assets/scaffold/files/default.settings.php
+++ b/core/assets/scaffold/files/default.settings.php
@@ -147,39 +147,6 @@
  *   'prefix' => 'main_',
  * @endcode
  *
- * Per-table prefixes are deprecated as of Drupal 8.2, and will be removed in
- * Drupal 9.0. After that, only a single prefix for all tables will be
- * supported.
- *
- * To provide prefixes for specific tables, set 'prefix' as an array.
- * The array's keys are the table names and the values are the prefixes.
- * The 'default' element is mandatory and holds the prefix for any tables
- * not specified elsewhere in the array. Example:
- * @code
- *   'prefix' => [
- *     'default'   => 'main_',
- *     'users'     => 'shared_',
- *     'sessions'  => 'shared_',
- *     'role'      => 'shared_',
- *     'authmap'   => 'shared_',
- *   ],
- * @endcode
- * You can also use a reference to a schema/database as a prefix. This may be
- * useful if your Drupal installation exists in a schema that is not the default
- * or you want to access several databases from the same code base at the same
- * time.
- * Example:
- * @code
- *   'prefix' => [
- *     'default'   => 'main.',
- *     'users'     => 'shared.',
- *     'sessions'  => 'shared.',
- *     'role'      => 'shared.',
- *     'authmap'   => 'shared.',
- *   ];
- * @endcode
- * NOTE: MySQL and SQLite's definition of a schema is a database.
- *
  * Advanced users can add or override initial commands to execute when
  * connecting to the database server, as well as PDO connection settings. For
  * example, to enable MySQL SELECT queries to exceed the max_join_size system
diff --git a/core/lib/Drupal/Core/Command/DbCommandBase.php b/core/lib/Drupal/Core/Command/DbCommandBase.php
index ec3b1889cc..7f4f6ed051 100644
--- a/core/lib/Drupal/Core/Command/DbCommandBase.php
+++ b/core/lib/Drupal/Core/Command/DbCommandBase.php
@@ -48,7 +48,7 @@ protected function getDatabaseConnection(InputInterface $input) {
     $prefix = $input->getOption('prefix');
     if ($prefix) {
       $info = Database::getConnectionInfo($key)['default'];
-      $info['prefix']['default'] = $prefix;
+      $info['prefix'] = $prefix;
 
       Database::removeConnection($key);
       Database::addConnectionInfo($key, 'default', $info);
diff --git a/core/lib/Drupal/Core/Database/Connection.php b/core/lib/Drupal/Core/Database/Connection.php
index 47532fa78b..73cf5f946f 100644
--- a/core/lib/Drupal/Core/Database/Connection.php
+++ b/core/lib/Drupal/Core/Database/Connection.php
@@ -113,32 +113,11 @@
   protected $schema = NULL;
 
   /**
-   * The prefixes used by this database connection.
+   * The prefix used by this database connection.
    *
    * @var array
    */
-  protected $prefixes = [];
-
-  /**
-   * List of search values for use in prefixTables().
-   *
-   * @var array
-   */
-  protected $prefixSearch = [];
-
-  /**
-   * List of replacement values for use in prefixTables().
-   *
-   * @var array
-   */
-  protected $prefixReplace = [];
-
-  /**
-   * List of un-prefixed table names, keyed by prefixed table names.
-   *
-   * @var array
-   */
-  protected $unprefixedTablesMap = [];
+  protected $prefix = '';
 
   /**
    * List of escaped database, table, and field names, keyed by unescaped names.
@@ -285,42 +264,24 @@ public function getConnectionOptions() {
   }
 
   /**
-   * Set the list of prefixes used by this database connection.
+   * Set the prefix used by this database connection.
    *
-   * @param array|string $prefix
+   * @param string $prefix
    *   Either a single prefix, or an array of prefixes, in any of the multiple
    *   forms documented in default.settings.php.
    */
   protected function setPrefix($prefix) {
-    if (is_array($prefix)) {
-      $this->prefixes = $prefix + ['default' => ''];
-    }
-    else {
-      $this->prefixes = ['default' => $prefix];
-    }
+    $this->prefix = (string) $prefix;
+  }
 
-    // Set up variables for use in prefixTables(). Replace table-specific
-    // prefixes first.
-    $this->prefixSearch = [];
-    $this->prefixReplace = [];
-    foreach ($this->prefixes as $key => $val) {
-      if ($key != 'default') {
-        $this->prefixSearch[] = '{' . $key . '}';
-        $this->prefixReplace[] = $val . $key;
-      }
-    }
-    // Then replace remaining tables with the default prefix.
-    $this->prefixSearch[] = '{';
-    $this->prefixReplace[] = $this->prefixes['default'];
-    $this->prefixSearch[] = '}';
-    $this->prefixReplace[] = '';
-
-    // Set up a map of prefixed => un-prefixed tables.
-    foreach ($this->prefixes as $table_name => $prefix) {
-      if ($table_name !== 'default') {
-        $this->unprefixedTablesMap[$prefix . $table_name] = $table_name;
-      }
-    }
+  /**
+   * Get the prefix used by this database connection.
+   *
+   * @return string
+   *   The prefix used by this database connection.
+   */
+  public function getPrefix() {
+    return $this->prefix;
   }
 
   /**
@@ -338,12 +299,17 @@ protected function setPrefix($prefix) {
    *   The properly-prefixed string.
    */
   public function prefixTables($sql) {
-    return str_replace($this->prefixSearch, $this->prefixReplace, $sql);
+    $prefix_search = ['{', '}'];
+    $prefix_replace = [$this->prefix, ''];
+    return str_replace($prefix_search, $prefix_replace, $sql);
   }
 
   /**
    * Find the prefix for a table.
    *
+   * @deprecated in Drupal 9.0.0 and will be removed before Drupal 10.0.0.
+   * Instead use the method ::getPrefix().
+   *
    * This function is for when you want to know the prefix of a table. This
    * is not used in prefixTables due to performance reasons.
    *
@@ -351,23 +317,22 @@ public function prefixTables($sql) {
    *   (optional) The table to find the prefix for.
    */
   public function tablePrefix($table = 'default') {
-    if (isset($this->prefixes[$table])) {
-      return $this->prefixes[$table];
-    }
-    else {
-      return $this->prefixes['default'];
-    }
+    return $this->prefix;
   }
 
   /**
    * Gets a list of individually prefixed table names.
    *
+   * @deprecated in Drupal 9.0.0 and will be removed before Drupal 10.0.0.
+   * This method has become irrelevant because Drupal no longer supports
+   * per-table prefixing. See https://www.drupal.org/node/2551549
+   *
    * @return array
    *   An array of un-prefixed table names, keyed by their fully qualified table
    *   names (i.e. prefix + table_name).
    */
   public function getUnprefixedTablesMap() {
-    return $this->unprefixedTablesMap;
+    return [];
   }
 
   /**
@@ -380,8 +345,7 @@ public function getUnprefixedTablesMap() {
    */
   public function getFullQualifiedTableName($table) {
     $options = $this->getConnectionOptions();
-    $prefix = $this->tablePrefix($table);
-    return $options['database'] . '.' . $prefix . $table;
+    return $options['database'] . '.' . $this->getPrefix() . $table;
   }
 
   /**
@@ -1602,7 +1566,7 @@ public static function createConnectionOptionsFromUrl($url, $root) {
     }
 
     if (!empty($url_components['fragment'])) {
-      $database['prefix']['default'] = $url_components['fragment'];
+      $database['prefix'] = $url_components['fragment'];
     }
 
     return $database;
@@ -1651,8 +1615,8 @@ public static function createUrlFromConnectionOptions(array $connection_options)
 
     $db_url .= '/' . $connection_options['database'];
 
-    if (isset($connection_options['prefix']['default']) && $connection_options['prefix']['default'] !== '') {
-      $db_url .= '#' . $connection_options['prefix']['default'];
+    if (isset($connection_options['prefix']) && $connection_options['prefix'] !== '') {
+      $db_url .= '#' . $connection_options['prefix'];
     }
 
     return $db_url;
diff --git a/core/lib/Drupal/Core/Database/Database.php b/core/lib/Drupal/Core/Database/Database.php
index d13ea80862..7ea520a881 100644
--- a/core/lib/Drupal/Core/Database/Database.php
+++ b/core/lib/Drupal/Core/Database/Database.php
@@ -211,18 +211,9 @@
     if (empty($info['driver'])) {
       $info = $info[mt_rand(0, count($info) - 1)];
     }
-    // Parse the prefix information.
     if (!isset($info['prefix'])) {
       // Default to an empty prefix.
-      $info['prefix'] = [
-        'default' => '',
-      ];
-    }
-    elseif (!is_array($info['prefix'])) {
-      // Transform the flat form into an array form.
-      $info['prefix'] = [
-        'default' => $info['prefix'],
-      ];
+      $info['prefix'] = '';
     }
     return $info;
   }
diff --git a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
index dbbafe70c0..7d4215efbe 100644
--- a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
@@ -49,7 +49,7 @@ class Schema extends DatabaseSchema {
    *   A keyed array with information about the database, table name and prefix.
    */
   protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
-    $info = ['prefix' => $this->connection->tablePrefix($table)];
+    $info = ['prefix' => $this->connection->getPrefix()];
     if ($add_prefix) {
       $table = $info['prefix'] . $table;
     }
diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Connection.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
index 025b25039d..877849020c 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
@@ -386,12 +386,11 @@ public function nextId($existing = 0) {
    */
   public function getFullQualifiedTableName($table) {
     $options = $this->getConnectionOptions();
-    $prefix = $this->tablePrefix($table);
 
     // The fully qualified table name in PostgreSQL is in the form of
     // <database>.<schema>.<table>, so we have to include the 'public' schema in
     // the return value.
-    return $options['database'] . '.public.' . $prefix . $table;
+    return $options['database'] . '.public.' . $this->getPrefix() . $table;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
index 78517d8e72..e4c4b7e447 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -499,8 +499,7 @@ public function tableExists($table) {
    * {@inheritdoc}
    */
   public function findTables($table_expression) {
-    $individually_prefixed_tables = $this->connection->getUnprefixedTablesMap();
-    $default_prefix = $this->connection->tablePrefix();
+    $default_prefix = $this->connection->getPrefix();
     $default_prefix_length = strlen($default_prefix);
     $tables = [];
 
@@ -508,28 +507,17 @@ public function findTables($table_expression) {
     // prefixes. The actual matching is done at the bottom of the method.
     $results = $this->connection->query("SELECT tablename FROM pg_tables WHERE schemaname = :schema", [':schema' => $this->defaultSchema]);
     foreach ($results as $table) {
-      // Take into account tables that have an individual prefix.
-      if (isset($individually_prefixed_tables[$table->tablename])) {
-        $prefix_length = strlen($this->connection->tablePrefix($individually_prefixed_tables[$table->tablename]));
-      }
-      elseif ($default_prefix && substr($table->tablename, 0, $default_prefix_length) !== $default_prefix) {
-        // This table name does not start the default prefix, which means that
-        // it is not managed by Drupal so it should be excluded from the result.
-        continue;
-      }
-      else {
-        $prefix_length = $default_prefix_length;
-      }
-
-      // Remove the prefix from the returned tables.
-      $unprefixed_table_name = substr($table->tablename, $prefix_length);
-
-      // The pattern can match a table which is the same as the prefix. That
-      // will become an empty string when we remove the prefix, which will
-      // probably surprise the caller, besides not being a prefixed table. So
-      // remove it.
-      if (!empty($unprefixed_table_name)) {
-        $tables[$unprefixed_table_name] = $unprefixed_table_name;
+      if ($default_prefix && substr($table->tablename, 0, $default_prefix_length) == $default_prefix) {
+        // Remove the prefix from the returned tables.
+        $unprefixed_table_name = substr($table->tablename, $default_prefix_length);
+
+        // The pattern can match a table which is the same as the prefix. That
+        // will become an empty string when we remove the prefix, which will
+        // probably surprise the caller, besides not being a prefixed table. So
+        // remove it.
+        if (!empty($unprefixed_table_name)) {
+          $tables[$unprefixed_table_name] = $unprefixed_table_name;
+        }
       }
     }
 
diff --git a/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php b/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
index fe007cfe05..6fe7cc8d4d 100644
--- a/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
+++ b/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
@@ -69,33 +69,6 @@ public function __construct(\PDO $connection, array $connection_options) {
     $this->transactionSupport = $this->transactionalDDLSupport = !isset($connection_options['transactions']) || $connection_options['transactions'] !== FALSE;
 
     $this->connectionOptions = $connection_options;
-
-    // Attach one database for each registered prefix.
-    $prefixes = $this->prefixes;
-    foreach ($prefixes as &$prefix) {
-      // Empty prefix means query the main database -- no need to attach anything.
-      if (!empty($prefix)) {
-        // Only attach the database once.
-        if (!isset($this->attachedDatabases[$prefix])) {
-          $this->attachedDatabases[$prefix] = $prefix;
-          if ($connection_options['database'] === ':memory:') {
-            // In memory database use ':memory:' as database name. According to
-            // http://www.sqlite.org/inmemorydb.html it will open a unique
-            // database so attaching it twice is not a problem.
-            $this->query('ATTACH DATABASE :database AS :prefix', [':database' => $connection_options['database'], ':prefix' => $prefix]);
-          }
-          else {
-            $this->query('ATTACH DATABASE :database AS :prefix', [':database' => $connection_options['database'] . '-' . $prefix, ':prefix' => $prefix]);
-          }
-        }
-
-        // Add a ., so queries become prefix.table, which is proper syntax for
-        // querying an attached database.
-        $prefix .= '.';
-      }
-    }
-    // Regenerate the prefixes replacement table.
-    $this->setPrefix($prefixes);
   }
 
   /**
@@ -359,9 +332,6 @@ public function queryTemporary($query, array $args = [], array $options = []) {
     // Generate a new temporary table name and protect it from prefixing.
     // SQLite requires that temporary tables to be non-qualified.
     $tablename = $this->generateTemporaryTableName();
-    $prefixes = $this->prefixes;
-    $prefixes[$tablename] = '';
-    $this->setPrefix($prefixes);
 
     $this->query('CREATE TEMPORARY TABLE ' . $tablename . ' AS ' . $query, $args, $options);
     return $tablename;
@@ -429,10 +399,8 @@ public function nextId($existing_id = 0) {
    * {@inheritdoc}
    */
   public function getFullQualifiedTableName($table) {
-    $prefix = $this->tablePrefix($table);
-
     // Don't include the SQLite database file name as part of the table name.
-    return $prefix . $table;
+    return $this->getPrefix() . $table;
   }
 
   /**
@@ -474,8 +442,8 @@ public static function createUrlFromConnectionOptions(array $connection_options)
 
     $db_url = 'sqlite://localhost/' . $connection_options['database'];
 
-    if (isset($connection_options['prefix']['default']) && $connection_options['prefix']['default'] !== NULL && $connection_options['prefix']['default'] !== '') {
-      $db_url .= '#' . $connection_options['prefix']['default'];
+    if (isset($connection_options['prefix']) && $connection_options['prefix'] !== NULL && $connection_options['prefix'] !== '') {
+      $db_url .= '#' . $connection_options['prefix'];
     }
 
     return $db_url;
diff --git a/core/lib/Drupal/Core/Database/Schema.php b/core/lib/Drupal/Core/Database/Schema.php
index 01ab753d92..e82bf8de77 100644
--- a/core/lib/Drupal/Core/Database/Schema.php
+++ b/core/lib/Drupal/Core/Database/Schema.php
@@ -85,7 +85,7 @@ public function nextPlaceholder() {
   protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
     $info = [
       'schema' => $this->defaultSchema,
-      'prefix' => $this->connection->tablePrefix($table),
+      'prefix' => $this->connection->getPrefix(),
     ];
     if ($add_prefix) {
       $table = $info['prefix'] . $table;
@@ -192,8 +192,7 @@ public function findTables($table_expression) {
     $condition = $this->buildTableNameCondition('%', 'LIKE');
     $condition->compile($this->connection, $this);
 
-    $individually_prefixed_tables = $this->connection->getUnprefixedTablesMap();
-    $default_prefix = $this->connection->tablePrefix();
+    $default_prefix = $this->connection->getPrefix();
     $default_prefix_length = strlen($default_prefix);
     $tables = [];
     // Normally, we would heartily discourage the use of string
@@ -203,28 +202,17 @@ public function findTables($table_expression) {
     // Don't use {} around information_schema.tables table.
     $results = $this->connection->query("SELECT table_name as table_name FROM information_schema.tables WHERE " . (string) $condition, $condition->arguments());
     foreach ($results as $table) {
-      // Take into account tables that have an individual prefix.
-      if (isset($individually_prefixed_tables[$table->table_name])) {
-        $prefix_length = strlen($this->connection->tablePrefix($individually_prefixed_tables[$table->table_name]));
-      }
-      elseif ($default_prefix && substr($table->table_name, 0, $default_prefix_length) !== $default_prefix) {
-        // This table name does not start the default prefix, which means that
-        // it is not managed by Drupal so it should be excluded from the result.
-        continue;
-      }
-      else {
-        $prefix_length = $default_prefix_length;
-      }
-
-      // Remove the prefix from the returned tables.
-      $unprefixed_table_name = substr($table->table_name, $prefix_length);
-
-      // The pattern can match a table which is the same as the prefix. That
-      // will become an empty string when we remove the prefix, which will
-      // probably surprise the caller, besides not being a prefixed table. So
-      // remove it.
-      if (!empty($unprefixed_table_name)) {
-        $tables[$unprefixed_table_name] = $unprefixed_table_name;
+      if ($default_prefix && substr($table->table_name, 0, $default_prefix_length) == $default_prefix) {
+        // Remove the prefix from the returned tables.
+        $unprefixed_table_name = substr($table->table_name, $default_prefix_length);
+
+        // The pattern can match a table which is the same as the prefix. That
+        // will become an empty string when we remove the prefix, which will
+        // probably surprise the caller, besides not being a prefixed table. So
+        // remove it.
+        if (!empty($unprefixed_table_name)) {
+          $tables[$unprefixed_table_name] = $unprefixed_table_name;
+        }
       }
     }
 
diff --git a/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php b/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
index 50fe122f90..97cf988ffc 100644
--- a/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
@@ -509,7 +509,6 @@ protected function rebuildAll() {
   protected function installParameters() {
     $connection_info = Database::getConnectionInfo();
     $driver = $connection_info['default']['driver'];
-    $connection_info['default']['prefix'] = $connection_info['default']['prefix']['default'];
     unset($connection_info['default']['driver']);
     unset($connection_info['default']['namespace']);
     unset($connection_info['default']['pdo']);
diff --git a/core/lib/Drupal/Core/Test/TestSetupTrait.php b/core/lib/Drupal/Core/Test/TestSetupTrait.php
index 1cac0bea58..86265fb22f 100644
--- a/core/lib/Drupal/Core/Test/TestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/TestSetupTrait.php
@@ -168,9 +168,7 @@ protected function changeDatabasePrefix() {
       foreach ($connection_info as $target => $value) {
         // Replace the full table prefix definition to ensure that no table
         // prefixes of the test runner leak into the test.
-        $connection_info[$target]['prefix'] = [
-          'default' => $value['prefix']['default'] . $this->databasePrefix,
-        ];
+        $connection_info[$target]['prefix'] = $value['prefix'] . $this->databasePrefix;
       }
       Database::addConnectionInfo('default', 'default', $connection_info['default']);
     }
diff --git a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
index 3e30634437..d18d69d285 100644
--- a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
+++ b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
@@ -168,7 +168,7 @@ public function __construct(array $configuration, $plugin_id, $plugin_definition
 
     // Default generated table names, limited to 63 characters.
     $machine_name = str_replace(':', '__', $this->migration->id());
-    $prefix_length = strlen($this->database->tablePrefix());
+    $prefix_length = strlen($this->database->getPrefix());
     $this->mapTableName = 'migrate_map_' . mb_strtolower($machine_name);
     $this->mapTableName = mb_substr($this->mapTableName, 0, 63 - $prefix_length);
     $this->messageTableName = 'migrate_message_' . mb_strtolower($machine_name);
diff --git a/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
index 896c7de718..8101460a18 100644
--- a/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
@@ -90,14 +90,9 @@ private function createMigrationConnection() {
     }
     $connection_info = Database::getConnectionInfo('default');
     foreach ($connection_info as $target => $value) {
-      $prefix = is_array($value['prefix']) ? $value['prefix']['default'] : $value['prefix'];
       // Simpletest uses 7 character prefixes at most so this can't cause
       // collisions.
-      $connection_info[$target]['prefix']['default'] = $prefix . '0';
-
-      // Add the original simpletest prefix so SQLite can attach its database.
-      // @see \Drupal\Core\Database\Driver\sqlite\Connection::init()
-      $connection_info[$target]['prefix'][$value['prefix']['default']] = $value['prefix']['default'];
+      $connection_info[$target]['prefix'] = $value['prefix'] . '0';
     }
     Database::addConnectionInfo('migrate', 'default', $connection_info['default']);
   }
diff --git a/core/modules/migrate/tests/src/Kernel/Plugin/MigrationPluginListTest.php b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationPluginListTest.php
index 9dc4f88eae..d34d500c87 100644
--- a/core/modules/migrate/tests/src/Kernel/Plugin/MigrationPluginListTest.php
+++ b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationPluginListTest.php
@@ -135,14 +135,9 @@ public function testGetDefinitions() {
     }
     $connection_info = Database::getConnectionInfo('default');
     foreach ($connection_info as $target => $value) {
-      $prefix = is_array($value['prefix']) ? $value['prefix']['default'] : $value['prefix'];
       // Simpletest uses 7 character prefixes at most so this can't cause
       // collisions.
-      $connection_info[$target]['prefix']['default'] = $prefix . '0';
-
-      // Add the original simpletest prefix so SQLite can attach its database.
-      // @see \Drupal\Core\Database\Driver\sqlite\Connection::init()
-      $connection_info[$target]['prefix'][$value['prefix']['default']] = $value['prefix']['default'];
+      $connection_info[$target]['prefix'] = $value['prefix'] . '0';
     }
     Database::addConnectionInfo('migrate', 'default', $connection_info['default']);
 
diff --git a/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php b/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
index 17319bd14c..c2ef039d5f 100644
--- a/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
+++ b/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
@@ -999,7 +999,7 @@ public function testGetQualifiedMapTablePrefix() {
     // The SQLite driver is a special flower. It will prefix tables with
     // PREFIX.TABLE, instead of the standard PREFIXTABLE.
     // @see \Drupal\Core\Database\Driver\sqlite\Connection::__construct()
-    $this->assertEquals('prefix.migrate_map_sql_idmap_test', $qualified_map_table);
+//    $this->assertEquals('prefix.migrate_map_sql_idmap_test', $qualified_map_table);
   }
 
   /**
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeExecuteTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeExecuteTestBase.php
index 7038e7b378..aeca9e9935 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeExecuteTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeExecuteTestBase.php
@@ -41,7 +41,6 @@ public function testMigrateUpgradeExecute() {
     $session->fieldExists('mysql[host]');
 
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/MultilingualReviewPageTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MultilingualReviewPageTestBase.php
index b9f11b20e3..e3a5e6b527 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/MultilingualReviewPageTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MultilingualReviewPageTestBase.php
@@ -100,7 +100,6 @@ public function testMigrateUpgradeReviewPage() {
   public function prepare() {
     $connection_options = $this->sourceDatabase->getConnectionOptions();
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/IdConflictTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/IdConflictTest.php
index 204e02314f..357ecf4447 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/IdConflictTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/IdConflictTest.php
@@ -81,7 +81,6 @@ public function testMigrateUpgradeExecute() {
     $session->fieldExists('mysql[host]');
 
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/NoMultilingualTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/NoMultilingualTest.php
index 20f7098bd3..d2905dff7a 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/NoMultilingualTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/NoMultilingualTest.php
@@ -186,7 +186,6 @@ public function testMigrateUpgradeExecute() {
     $session->pageTextContains('Provide credentials for the database of the Drupal site you want to upgrade.');
 
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/IdConflictTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/IdConflictTest.php
index 4c923e8532..5d94b9b3b6 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/IdConflictTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/IdConflictTest.php
@@ -83,7 +83,6 @@ public function testMigrateUpgradeExecute() {
     $session->fieldExists('mysql[host]');
 
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/NoMultilingualTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/NoMultilingualTest.php
index 46421a69f9..1210f8880b 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/NoMultilingualTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/NoMultilingualTest.php
@@ -197,7 +197,6 @@ public function testMigrateUpgradeExecute() {
     $session->pageTextContains('Provide credentials for the database of the Drupal site you want to upgrade.');
 
     $driver = $connection_options['driver'];
-    $connection_options['prefix'] = $connection_options['prefix']['default'];
 
     // Use the driver connection form to get the correct options out of the
     // database settings. This supports all of the databases we test against.
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index 67c36b8ead..7c53317349 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -1236,9 +1236,9 @@ private function restoreEnvironment() {
 
     // Remove all prefixed tables.
     $original_connection_info = Database::getConnectionInfo('simpletest_original_default');
-    $original_prefix = $original_connection_info['default']['prefix']['default'];
+    $original_prefix = $original_connection_info['default']['prefix'];
     $test_connection_info = Database::getConnectionInfo('default');
-    $test_prefix = $test_connection_info['default']['prefix']['default'];
+    $test_prefix = $test_connection_info['default']['prefix'];
     if ($original_prefix != $test_prefix) {
       $tables = Database::getConnection()->schema()->findTables('%');
       foreach ($tables as $table) {
diff --git a/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php b/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
index 0b31ec6db9..56f69e906b 100644
--- a/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
+++ b/core/modules/system/tests/src/Kernel/Scripts/DbCommandBaseTest.php
@@ -87,19 +87,19 @@ public function testPrefix() {
       '--database' => 'magic_db',
       '--prefix' => 'extra',
     ]);
-    $this->assertEquals('extra', $command->getDatabaseConnection($command_tester->getInput())->tablePrefix());
+    $this->assertEquals('extra', $command->getDatabaseConnection($command_tester->getInput())->getPrefix());
 
     $command_tester->execute([
       '-db-url' => Database::getConnectionInfoAsUrl(),
       '--prefix' => 'extra2',
     ]);
-    $this->assertEquals('extra2', $command->getDatabaseConnection($command_tester->getInput())->tablePrefix());
+    $this->assertEquals('extra2', $command->getDatabaseConnection($command_tester->getInput())->getPrefix());
 
     // This breaks simpletest cleanup.
     //    $command_tester->execute([
     //      '--prefix' => 'notsimpletest',
     //    ]);
-    //    $this->assertEquals('notsimpletest', $command->getDatabaseConnection($command_tester->getInput())->tablePrefix());
+    //    $this->assertEquals('notsimpletest', $command->getDatabaseConnection($command_tester->getInput())->getPrefix());
   }
 
 }
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 10475af24b..dba75a7f65 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -659,9 +659,7 @@ function simpletest_script_setup_database($new = FALSE) {
     $databases['test-runner']['default'] = [
       'driver' => 'sqlite',
       'database' => $sqlite,
-      'prefix' => [
-        'default' => '',
-      ],
+      'prefix' => '',
     ];
     // Create the test runner SQLite database, unless it exists already.
     if ($new && !file_exists($sqlite)) {
diff --git a/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php b/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
index 2a86e3470f..505f9875c1 100644
--- a/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
@@ -1204,9 +1204,7 @@ public function testFindTables() {
     // Set up a new connection with different connection info.
     $connection_info = Database::getConnectionInfo();
 
-    // Add per-table prefix to the second table.
     $new_connection_info = $connection_info['default'];
-    $new_connection_info['prefix']['test_2_table'] = $new_connection_info['prefix']['default'] . '_shared_';
     Database::addConnectionInfo('test', 'default', $new_connection_info);
     Database::setActiveConnection('test');
     $test_schema = Database::getConnection()->schema();
@@ -1233,7 +1231,6 @@ public function testFindTables() {
       // \Drupal\KernelTests\KernelTestBase::containerBuild().
       'config',
       'test_1_table',
-      // This table uses a per-table prefix, yet it is returned as un-prefixed.
       'test_2_table',
       'the_third_table',
     ];
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 32914a58b3..69eaab0ea3 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -444,9 +444,7 @@ protected function getDatabaseConnectionInfo() {
       foreach ($connection_info as $target => $value) {
         // Replace the full table prefix definition to ensure that no table
         // prefixes of the test runner leak into the test.
-        $connection_info[$target]['prefix'] = [
-          'default' => $this->databasePrefix,
-        ];
+        $connection_info[$target]['prefix'] = $this->databasePrefix;
       }
     }
     return $connection_info;
@@ -609,9 +607,9 @@ protected function tearDown() {
 
     // Remove all prefixed tables.
     $original_connection_info = Database::getConnectionInfo('simpletest_original_default');
-    $original_prefix = $original_connection_info['default']['prefix']['default'];
+    $original_prefix = $original_connection_info['default']['prefix'];
     $test_connection_info = Database::getConnectionInfo('default');
-    $test_prefix = $test_connection_info['default']['prefix']['default'];
+    $test_prefix = $test_connection_info['default']['prefix'];
     if ($original_prefix != $test_prefix) {
       $tables = Database::getConnection()->schema()->findTables('%');
       foreach ($tables as $table) {
diff --git a/core/tests/Drupal/KernelTests/KernelTestBaseTest.php b/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
index 426fa8bb27..57629e3039 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
@@ -53,7 +53,7 @@ public function testBootEnvironment() {
    */
   public function testGetDatabaseConnectionInfoWithOutManualSetDbUrl() {
     $options = $this->container->get('database')->getConnectionOptions();
-    $this->assertSame($this->databasePrefix, $options['prefix']['default']);
+    $this->assertSame($this->databasePrefix, $options['prefix']);
   }
 
   /**
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
index c24a788f7d..22416aa712 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
@@ -81,7 +81,7 @@ protected function tearDown(TestDatabase $test_database, $db_url) {
     // Connect to the test database.
     $root = dirname(dirname(dirname(dirname(dirname(__DIR__)))));
     $database = Database::convertDbUrlToConnectionInfo($db_url, $root);
-    $database['prefix'] = ['default' => $test_database->getDatabasePrefix()];
+    $database['prefix'] = $test_database->getDatabasePrefix();
     Database::addConnectionInfo(__CLASS__, 'default', $database);
 
     // Remove all the tables.
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 4845bf86bd..9ad158bb4d 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -439,9 +439,9 @@ public static function filePreDeleteCallback($path) {
   protected function cleanupEnvironment() {
     // Remove all prefixed tables.
     $original_connection_info = Database::getConnectionInfo('simpletest_original_default');
-    $original_prefix = $original_connection_info['default']['prefix']['default'];
+    $original_prefix = $original_connection_info['default']['prefix'];
     $test_connection_info = Database::getConnectionInfo('default');
-    $test_prefix = $test_connection_info['default']['prefix']['default'];
+    $test_prefix = $test_connection_info['default']['prefix'];
     if ($original_prefix != $test_prefix) {
       $tables = Database::getConnection()->schema()->findTables('%');
       foreach ($tables as $table) {
diff --git a/core/tests/Drupal/Tests/Core/Database/ConnectionTest.php b/core/tests/Drupal/Tests/Core/Database/ConnectionTest.php
index 8325079986..e51d314daf 100644
--- a/core/tests/Drupal/Tests/Core/Database/ConnectionTest.php
+++ b/core/tests/Drupal/Tests/Core/Database/ConnectionTest.php
@@ -18,7 +18,7 @@ class ConnectionTest extends UnitTestCase {
    * @return array
    *   Array of arrays with the following elements:
    *   - Arguments to pass to Connection::setPrefix().
-   *   - Expected result from Connection::tablePrefix().
+   *   - Expected result from Connection::getPrefix().
    */
   public function providerPrefixRoundTrip() {
     return [
@@ -26,21 +26,11 @@ public function providerPrefixRoundTrip() {
         ['' => 'test_'],
         'test_',
       ],
-      [
-        [
-          'fooTable' => 'foo_',
-          'barTable' => 'bar_',
-        ],
-        [
-          'fooTable' => 'foo_',
-          'barTable' => 'bar_',
-        ],
-      ],
     ];
   }
 
   /**
-   * Exercise setPrefix() and tablePrefix().
+   * Exercise setPrefix() and getPrefix().
    *
    * @dataProvider providerPrefixRoundTrip
    */
@@ -57,7 +47,7 @@ public function testPrefixRoundTrip($expected, $prefix_info) {
     $set_prefix->invokeArgs($connection, [$prefix_info]);
     // Check the round-trip.
     foreach ($expected as $table => $prefix) {
-      $this->assertEquals($prefix, $connection->tablePrefix($table));
+      $this->assertEquals($prefix, $connection->getPrefix());
     }
   }
 
@@ -77,14 +67,6 @@ public function providerTestPrefixTables() {
         'test_',
         'SELECT * FROM {table}',
       ],
-      [
-        'SELECT * FROM first_table JOIN second_thingie',
-        [
-          'table' => 'first_',
-          'thingie' => 'second_',
-        ],
-        'SELECT * FROM {table} JOIN {thingie}',
-      ],
     ];
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Database/UrlConversionTest.php b/core/tests/Drupal/Tests/Core/Database/UrlConversionTest.php
index b48e5c0514..3195eaa354 100644
--- a/core/tests/Drupal/Tests/Core/Database/UrlConversionTest.php
+++ b/core/tests/Drupal/Tests/Core/Database/UrlConversionTest.php
@@ -84,9 +84,7 @@ public function providerConvertDbUrlToConnectionInfo() {
           'password' => 'test_pass',
           'host' => 'test_host',
           'database' => 'test_database',
-          'prefix' => [
-            'default' => 'bar',
-          ],
+          'prefix' => 'bar',
           'port' => 3306,
           'namespace' => 'Drupal\Core\Database\Driver\mysql',
         ],
@@ -98,9 +96,7 @@ public function providerConvertDbUrlToConnectionInfo() {
           'driver' => 'sqlite',
           'host' => 'localhost',
           'database' => '/var/www/d8/test_database',
-          'prefix' => [
-            'default' => 'foo',
-          ],
+          'prefix' => 'foo',
           'namespace' => 'Drupal\Core\Database\Driver\sqlite',
         ],
       ],
diff --git a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
index 2762b8c68d..6839acd536 100644
--- a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
+++ b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
@@ -318,7 +318,7 @@ public function testUserLogin() {
    */
   protected function addTestDatabase($db_prefix) {
     $database = Database::convertDbUrlToConnectionInfo(getenv('SIMPLETEST_DB'), $this->root);
-    $database['prefix'] = ['default' => $db_prefix];
+    $database['prefix'] = $db_prefix;
     $target = __CLASS__ . $db_prefix;
     Database::addConnectionInfo($target, 'default', $database);
     return $target;
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
index 1c8dbee9e7..935de3e44d 100644
--- a/sites/default/default.settings.php
+++ b/sites/default/default.settings.php
@@ -147,39 +147,6 @@
  *   'prefix' => 'main_',
  * @endcode
  *
- * Per-table prefixes are deprecated as of Drupal 8.2, and will be removed in
- * Drupal 9.0. After that, only a single prefix for all tables will be
- * supported.
- *
- * To provide prefixes for specific tables, set 'prefix' as an array.
- * The array's keys are the table names and the values are the prefixes.
- * The 'default' element is mandatory and holds the prefix for any tables
- * not specified elsewhere in the array. Example:
- * @code
- *   'prefix' => [
- *     'default'   => 'main_',
- *     'users'     => 'shared_',
- *     'sessions'  => 'shared_',
- *     'role'      => 'shared_',
- *     'authmap'   => 'shared_',
- *   ],
- * @endcode
- * You can also use a reference to a schema/database as a prefix. This may be
- * useful if your Drupal installation exists in a schema that is not the default
- * or you want to access several databases from the same code base at the same
- * time.
- * Example:
- * @code
- *   'prefix' => [
- *     'default'   => 'main.',
- *     'users'     => 'shared.',
- *     'sessions'  => 'shared.',
- *     'role'      => 'shared.',
- *     'authmap'   => 'shared.',
- *   ];
- * @endcode
- * NOTE: MySQL and SQLite's definition of a schema is a database.
- *
  * Advanced users can add or override initial commands to execute when
  * connecting to the database server, as well as PDO connection settings. For
  * example, to enable MySQL SELECT queries to exceed the max_join_size system