diff --git a/publication_date.info.yml b/publication_date.info.yml
index d3eaf0f..e502ace 100644
--- a/publication_date.info.yml
+++ b/publication_date.info.yml
@@ -3,3 +3,6 @@ description: "Add a field containing the publication date."
 type: module
 core: 8.x
 configure: admin/config/content/publication-date
+
+dependencies:
+  - drupal:node
diff --git a/publication_date.install b/publication_date.install
index 1cb9fcb..30668d4 100755
--- a/publication_date.install
+++ b/publication_date.install
@@ -5,32 +5,201 @@
  * Installation functions for the Publication Date module.
  */
 
+use Drupal\Core\Database\Driver\mysql\Connection as MysqlConnection;
+use Drupal\Core\Database\Driver\pgsql\Connection as PgsqlConnection;
+use Drupal\Core\Messenger\MessengerInterface;
+
 /**
  * Implements hook_install().
  */
 function publication_date_install() {
-  // Set publication dates for existing nodes.
-  _publication_date_update_existing();
+  // Populate the publication date field with the timestamp of the first
+  // published revision.
+  _publication_date_populate_database_field();
 
   // This module must be called after some other modules (i.e. Scheduler).
   module_set_weight('publication_date', 99);
 }
 
 /**
- * Helper function to update the existing nodes on install.
+ * Helper function to populate the published on date for unpublished nodes.
  *
- * We can not know the exact date of publication, so $node->published_at will
- * initially contain the creation date for already publisned nodes.
+ * This function makes sure that all existing nodes have the publication date
+ * set. The publication date is derived from the first published revision.
  */
-function _publication_date_update_existing() {
-  // @todo: Convert to entity query.
-  return;
-
-  $query = db_select('node');
-  $query->addField('node', 'nid');
-  $query->addField('node', 'created', 'published_at');
-  $nids = $query->condition('status', 1);
-  db_insert('publication_date')
-    ->from($nids)
-    ->execute();
+function _publication_date_populate_database_field() {
+  $connection = \Drupal::database();
+
+  // The Drupal database API does not yet support update queries that use joins,
+  // meaning that this operation needs to be implemented using direct queries.
+  // It is currently tested only for MySQL, MariaDB, and Postgres.
+  if ($connection instanceof MysqlConnection) {
+    $queries = [
+      // Update nodes with multiple revisions that have at least one published
+      // revision so the publication date is set to the timestamp of the first
+      // published revision.
+      [
+        'query' => <<<SQL
+UPDATE
+  {node_field_revision} r,
+  {node_revision} s,
+  (
+    SELECT
+      nid,
+      MIN(vid) as vid
+    FROM {node_field_revision}
+    WHERE status = 1
+    GROUP BY nid
+    ORDER BY vid
+  ) t
+SET r.published_at = s.revision_timestamp
+WHERE
+  r.nid = t.nid
+  AND s.nid = t.nid
+  AND s.vid = t.vid
+  AND r.vid >= t.vid;
+SQL
+        ,
+        'arguments' => [],
+      ],
+
+      // Update the revisions table so that nodes that have a single published
+      // revision have the publication timestamp set to the creation timestamp.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_revision} r, (
+  SELECT nid
+  FROM {node_field_revision}
+  GROUP BY nid
+  HAVING COUNT(*) = 1
+) s
+SET r.published_at = r.created
+WHERE
+  r.nid = s.nid
+  AND r.status = 1
+SQL
+        ,
+        'arguments' => [],
+      ],
+
+      // Set the remainder of the publication dates in the revisions table to the
+      // default timestamp. This applies to all revisions that were created before
+      // the node was first published.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_revision} r
+SET r.published_at = :default_timestamp
+WHERE r.published_at IS NULL;
+SQL
+        ,
+        'arguments' => [':default_timestamp' => PUBLICATION_DATE_DEFAULT],
+      ],
+
+      // Copy the publication date from the revisions table to the node table.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_data} d, {node_field_revision} r
+SET d.published_at = r.published_at
+WHERE d.vid = r.vid;
+SQL
+        ,
+        'arguments' => [],
+      ],
+    ];
+  } 
+  elseif ($connection instanceof PgsqlConnection) {
+    $queries = [
+      // Update nodes with multiple revisions that have at least one published
+      // revision so the publication date is set to the timestamp of the first
+      // published revision.
+      [
+        'query' => <<<SQL
+UPDATE
+  {node_field_revision} r
+SET published_at = s.revision_timestamp
+FROM
+  {node_revision} s,
+  (
+    SELECT
+      nid,
+      MIN(vid) as vid
+    FROM {node_field_revision}
+    WHERE status = 1
+    GROUP BY nid
+    ORDER BY vid
+  ) t
+WHERE
+  r.nid = t.nid
+  AND s.nid = t.nid
+  AND s.vid = t.vid
+  AND r.vid >= t.vid;
+SQL
+        ,
+        'arguments' => [],
+      ],
+
+      // Update the revisions table so that nodes that have a single published
+      // revision have the publication timestamp set to the creation timestamp.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_revision} r
+SET published_at = r.created
+FROM
+  (
+    SELECT nid
+    FROM {node_field_revision}
+    GROUP BY nid
+    HAVING COUNT(*) = 1
+  ) s
+WHERE
+  r.nid = s.nid
+  AND r.status = 1
+SQL
+        ,
+        'arguments' => [],
+      ],
+
+      // Set the remainder of the publication dates in the revisions table to the
+      // default timestamp. This applies to all revisions that were created before
+      // the node was first published.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_revision} r
+SET published_at = :default_timestamp
+WHERE r.published_at IS NULL;
+SQL
+        ,
+        'arguments' => [':default_timestamp' => PUBLICATION_DATE_DEFAULT],
+      ],
+
+      // Copy the publication date from the revisions table to the node table.
+      [
+        'query' => <<<SQL
+UPDATE {node_field_data} d
+SET published_at = r.published_at
+FROM {node_field_revision} r
+WHERE d.vid = r.vid;
+SQL
+        ,
+        'arguments' => [],
+      ],
+    ];
+  }
+  else {
+    $message = t('Populating the publication date on existing nodes is currently only supported on MySQL and Postgres databases.');
+    \Drupal::messenger()->addMessage($message, MessengerInterface::TYPE_WARNING);
+    return;
+  }
+
+  // Perform the operations in a single atomic transaction.
+  $transaction = $connection->startTransaction();
+  try {
+    foreach ($queries as $query_data) {
+      \Drupal::database()->query($query_data['query'], $query_data['arguments']);
+    }
+  }
+  catch (Exception $e) {
+    $transaction->rollBack();
+    throw new Exception('Database error', 0, $e);
+  }
 }
diff --git a/publication_date.post_update.php b/publication_date.post_update.php
new file mode 100755
index 0000000..687aa50
--- /dev/null
+++ b/publication_date.post_update.php
@@ -0,0 +1,16 @@
+<?php
+
+/**
+ * @file
+ * Post update functions for the Publication Date module.
+ */
+
+/**
+ * Populate the publication dates.
+ */
+function publication_date_post_update_populate_publication_dates() {
+  $module_path = DRUPAL_ROOT . '/' . drupal_get_path('module', 'publication_date') . '/publication_date.install';
+  require_once $module_path;
+
+  _publication_date_populate_database_field();
+}
diff --git a/src/Plugin/Field/FieldType/PublicationDateItem.php b/src/Plugin/Field/FieldType/PublicationDateItem.php
index eac5833..4e4e8a3 100644
--- a/src/Plugin/Field/FieldType/PublicationDateItem.php
+++ b/src/Plugin/Field/FieldType/PublicationDateItem.php
@@ -1,14 +1,8 @@
 <?php
 
-/**
- * @file
- * Contains \Drupal\publication_date\Plugin\Field\FieldType\PublicationDateItem.
- */
-
 namespace Drupal\publication_date\Plugin\Field\FieldType;
 
 use Drupal\Core\Entity\EntityPublishedInterface;
-use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Field\Plugin\Field\FieldType\ChangedItem;
 use Drupal\Core\TypedData\DataDefinition;
@@ -42,7 +36,7 @@ class PublicationDateItem extends ChangedItem {
   }
 
   /**
-   * @inheritDoc
+   * {@inheritdoc}
    */
   public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
     $properties = parent::propertyDefinitions($field_definition);
@@ -77,13 +71,16 @@ class PublicationDateItem extends ChangedItem {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
   protected function isPublished() {
     $entity = $this->getEntity();
     return ($entity instanceof EntityPublishedInterface) ? $entity->isPublished() : FALSE;
   }
 
   /**
-   * @inheritDoc
+   * {@inheritdoc}
    */
   public function isEmpty() {
     return FALSE;
diff --git a/tests/src/Functional/PublicationDateInstallationTest.php b/tests/src/Functional/PublicationDateInstallationTest.php
new file mode 100644
index 0000000..432511a
--- /dev/null
+++ b/tests/src/Functional/PublicationDateInstallationTest.php
@@ -0,0 +1,98 @@
+<?php
+
+namespace Drupal\Tests\publication_date\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests publication_date install hook.
+ *
+ * @group publication_date
+ */
+class PublicationDateInstallationTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+  ];
+
+  /**
+   * Tests that the publication date is correctly set on enabling of the module.
+   */
+  public function testPublicationDateInstall() {
+    // Create a node that starts out as published.
+    $published = $this->createNode(['status' => 1]);
+
+    // Create a node that was never published.
+    $unpublished = $this->createNode(['status' => 0]);
+
+    // Create a node that only has one revision but has been edited after being
+    // created. As a result the changed time is later than the creation time.
+    $single_revision = $this->createNode(['status' => 1]);
+    $single_revision->setNewRevision(FALSE);
+    $single_revision->setCreatedTime(strtotime('2019-06-10 10:00'));
+    $single_revision->setChangedTime(strtotime('2019-07-20 10:00'));
+    $single_revision->save();
+
+    // Create a node that is currently unpublished but has been published in a
+    // previous revision. Start with an unpublished revision.
+    $previously_published = $this->createNode(['status' => 0]);
+
+    // Create an published revision.
+    $previously_published->setNewRevision();
+    $previously_published->setPublished();
+    $previously_published->setRevisionCreationTime(strtotime('2019-07-20 10:00'));
+    $previously_published->save();
+
+    // Create a final unpublished revision.
+    $previously_published->setNewRevision();
+    $previously_published->setUnpublished();
+    $previously_published->setRevisionCreationTime(strtotime('2019-07-20 11:00'));
+    $previously_published->save();
+
+    // Install the module. This should populate our 'published_at' field data.
+    $this->container->get('module_installer')->install(['publication_date']);
+
+    // The published node should have the right publication time set.
+    $this->assertEquals($published->getCreatedTime(), $this->select('node_field_data')->condition('nid', $published->id())->fields('node_field_data', ['published_at'])->execute()->fetchField());
+
+    // The unpublished node should have the default publication time.
+    $this->assertEquals(PUBLICATION_DATE_DEFAULT, $this->select('node_field_data')->condition('nid', $unpublished->id())->fields('node_field_data', ['published_at'])->execute()->fetchField());
+
+    // The node with a single revision which has been changed later should have
+    // the publication time set to the time the node was created.
+    $this->assertEquals($single_revision->getCreatedTime(), $this->select('node_field_data')->condition('nid', $single_revision->id())->fields('node_field_data', ['published_at'])->execute()->fetchField());
+
+    // The previously published node should have the right publication time.
+    $this->assertEquals(strtotime('2019-07-20 10:00'), $this->select('node_field_data')->condition('nid', $previously_published->id())->fields('node_field_data', ['published_at'])->execute()->fetchField());
+
+    // The first revision of the previously published node was unpublished, so
+    // it should have the default publication time.
+    $revision_ids = $this->container->get('entity_type.manager')->getStorage('node')->revisionIds($previously_published);
+    $this->assertEquals(PUBLICATION_DATE_DEFAULT, $this->select('node_field_revision')->condition('vid', $revision_ids[0])->fields('node_field_revision', ['published_at'])->execute()->fetchField());
+
+    // The second revision of the previously published node was the first
+    // published revision, so it should have the publication time.
+    $this->assertEquals(strtotime('2019-07-20 10:00'), $this->select('node_field_revision')->condition('vid', $revision_ids[1])->fields('node_field_revision', ['published_at'])->execute()->fetchField());
+
+    // The third revision of the previously published node is unpublished, but
+    // should have the publication time set.
+    $this->assertEquals(strtotime('2019-07-20 10:00'), $this->select('node_field_revision')->condition('vid', $revision_ids[2])->fields('node_field_revision', ['published_at'])->execute()->fetchField());
+  }
+
+  /**
+   * Returns a select query for the given database table.
+   *
+   * @param string $table
+   *   The database table for which to return the query.
+   *
+   * @return \Drupal\Core\Database\Query\SelectInterface
+   *   The select query.
+   */
+  protected function select($table) {
+    return $this->container->get('database')->select($table);
+  }
+
+}