interdiff impossible; taking evasive action
reverted:
--- b/core/lib/Drupal/Core/Database/Connection.php
+++ a/core/lib/Drupal/Core/Database/Connection.php
@@ -497,45 +497,6 @@
     return $this->prefixTables('{' . $table . '}_' . $field . '_seq');
   }
 
-  /**
-   * Retrieves a sequence owned by a table and column.
-   *
-   * @param string $table
-   *   A table name that is not prefixed or quoted.
-   * @param string $column
-   *   The column name.
-   *
-   * @return string|null
-   *   The name of the sequence or NULL if it does not exist.
-   */
-  public function getSequence($table, $column) {
-    $args = [
-      ':table' => $this->prefixTables('{' . $table . '}'),
-      ':column' => $column,
-    ];
-    return $this
-      ->query("SELECT pg_get_serial_sequence(:table, :column)", $args)
-      ->fetchField();
-  }
-
-  /**
-   * Checks if a sequence exists at all.
-   *
-   * @param string $name
-   *   The fully-qualified sequence name.
-   *
-   * @return bool
-   *   TRUE if the sequence exists by the name.
-   *
-   * @see \Drupal\Core\Database\Connection::makeSequenceName()
-   */
-  public function sequenceExists($name) {
-    $args = [':name' => $name];
-    return (bool) $this
-      ->query("SELECT c.relname FROM pg_class as c INNER JOIN pg_namespace as ns ON (c.relnamespace = ns.oid) WHERE c.relkind = 'S' AND c.relname = :name", $args)
-      ->fetchField();
-  }
-
   /**
    * Flatten an array of query comments into a single comment string.
    *
unchanged:
--- a/core/lib/Drupal/Core/Database/Connection.php
+++ b/core/lib/Drupal/Core/Database/Connection.php
@@ -490,6 +490,45 @@ public function makeSequenceName($table, $field) {
     return $this->prefixTables('{' . $table . '}_' . $field . '_seq');
   }
 
+  /**
+   * Retrieves a sequence owned by a table and column.
+   *
+   * @param string $table
+   *   A table name that is not prefixed or quoted.
+   * @param string $column
+   *   The column name.
+   *
+   * @return string|null
+   *   The name of the sequence or NULL if it does not exist.
+   */
+  public function getSequence($table, $column) {
+    $args = [
+      ':table' => $this->prefixTables('{' . $table . '}'),
+      ':column' => $column,
+    ];
+    return $this
+      ->query("SELECT pg_get_serial_sequence(:table, :column)", $args)
+      ->fetchField();
+  }
+
+  /**
+   * Checks if a sequence exists at all.
+   *
+   * @param string $name
+   *   The fully-qualified sequence name.
+   *
+   * @return bool
+   *   TRUE if the sequence exists by the name.
+   *
+   * @see \Drupal\Core\Database\Connection::makeSequenceName()
+   */
+  public function sequenceExists($name) {
+    $args = [':name' => $name];
+    return (bool) $this
+      ->query("SELECT c.relname FROM pg_class as c INNER JOIN pg_namespace as ns ON (c.relnamespace = ns.oid) WHERE c.relkind = 'S' AND c.relname = :name", $args)
+      ->fetchField();
+  }
+
   /**
    * Flatten an array of query comments into a single comment string.
    *
diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -2361,7 +2361,7 @@
 /**
  * Fix any orphan sequences created from column changes in PostgreSQL.
  */
-function system_update_8801(&$sandbox) {
+function system_update_8802(&$sandbox) {
   $connection = \Drupal::database();
   if ($connection->databaseType() !== 'pgsql') {
     // This database update is a no-op for all other core database drivers.
@@ -2383,7 +2383,7 @@
         if (!empty($schema)) {
           foreach ($schema as $table_name => $table_info) {
             foreach ($table_info['fields'] as $column_name => $column_info) {
-              if (substr($column_info['type'], 0, 6) === 'serial') {
+              if (substr($column_info['type'], 0, 6) === 'serial' && $connection->schema()->tableExists($table_name)) {
                 $sandbox['tables'][] = [
                   'table' => $table_name,
                   'column' => $column_name,
@@ -2408,7 +2408,8 @@
 
         /** @var \Drupal\Core\Field\BaseFieldDefinition[] $baseFieldDefinitions */
         $baseFieldDefinitions = $entity_class::baseFieldDefinitions($entity_type);
-        if ($baseFieldDefinitions[$id_key]->getType() === 'integer') {
+        if ($baseFieldDefinitions[$id_key]->getType() === 'integer' &&
+            $connection->schema()->tableExists($table_name)) {
           $sandbox['tables'][] = [
             'table' => $entity_type->getBaseTable(),
             'column' => $id_key,
@@ -2416,7 +2417,8 @@
         }
 
         if ($entity_type->isRevisionable() &&
-          $baseFieldDefinitions[$revision_key]->getType() === 'integer') {
+          $baseFieldDefinitions[$revision_key]->getType() === 'integer' &&
+          $connection->schema()->tableExists($table_name)) {
           $sandbox['tables'][] = [
             'table' => $entity_type->getRevisionTable(),
             'column' => $revision_key,
@@ -2475,0 +2478 @@
+