ntity_id ] = array();
					}
					$to_insert[ $entity_id ][ $meta_key ] = $meta_values;
				} else {
					if ( 1 === count( $meta_values ) && 1 === count( $already_migrated[ $entity_id ][ $meta_key ] ) ) {
						if ( $meta_values[0] === $already_migrated[ $entity_id ][ $meta_key ][0]['meta_value'] ) {
							continue;
						}
						if ( ! isset( $to_update[ $entity_id ] ) ) {
							$to_update[ $entity_id ] = array();
						}
						$to_update[ $entity_id ][ $meta_key ] = array(
							'id'         => $already_migrated[ $entity_id ][ $meta_key ][0]['id'],
							// phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_meta_value
							'meta_value' => $meta_values[0],
						);
						continue;
					}

					// There are multiple meta entries, let's find the unique entries and insert.
					$unique_meta_values = array_diff( $meta_values, array_column( $already_migrated[ $entity_id ][ $meta_key ], 'meta_value' ) );
					if ( 0 === count( $unique_meta_values ) ) {
						continue;
					}
					if ( ! isset( $to_insert[ $entity_id ] ) ) {
						$to_insert[ $entity_id ] = array();
					}
					$to_insert[ $entity_id ][ $meta_key ] = $unique_meta_values;
				}
			}
		}

		return array( $to_insert, $to_update );
	}

	/**
	 * Helper method to build query used to fetch data from source meta table.
	 *
	 * @param array $entity_ids List of entity IDs to build meta query for.
	 *
	 * @return string Query that can be used to fetch data.
	 */
	private function build_meta_table_query( array $entity_ids ): string {
		global $wpdb;
		$source_meta_table        = $this->schema_config['source']['meta']['table_name'];
		$source_meta_key_column   = $this->schema_config['source']['meta']['meta_key_column'];
		$source_meta_value_column = $this->schema_config['source']['meta']['meta_value_column'];
		$source_entity_id_column  = $this->schema_config['source']['meta']['entity_id_column'];
		$order_by                 = "source.$source_entity_id_column ASC";

		$where_clause = "source.`$source_entity_id_column` IN (" . implode( ', ', array_fill( 0, count( $entity_ids ), '%d' ) ) . ')';

		$entity_table                  = $this->schema_config['source']['entity']['table_name'];
		$entity_id_column              = $this->schema_config['source']['entity']['id_column'];
		$entity_meta_id_mapping_column = $this->schema_config['source']['entity']['source_id_column'];

		if ( isset( $this->schema_config['source']['excluded_keys'] ) && is_array( $this->schema_config['source']['excluded_keys'] ) ) {
			$key_placeholder = implode( ',', array_fill( 0, count( $this->schema_config['source']['excluded_keys'] ), '%s' ) );
			// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare -- $source_meta_key_column is escaped for backticks, $key_placeholder is hardcoded.
			$exclude_clause = $wpdb->prepare( "source.$source_meta_key_column NOT IN ( $key_placeholder )", $this->schema_config['source']['excluded_keys'] );
			$where_clause   = "$where_clause AND $exclude_clause";
		}

		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
		return $wpdb->prepare(
			"
SELECT
	source.`$source_entity_id_column` as source_entity_id,
	entity.`$entity_id_column` as entity_id,
	source.`$source_meta_key_column` as meta_key,
	source.`$source_meta_value_column` as meta_value
FROM `$source_meta_table` source
JOIN `$entity_table` entity ON entity.`$entity_meta_id_mapping_column` = source.`$source_entity_id_column`
WHERE $where_clause ORDER BY $order_by
",
			$entity_ids
		);
		// phpcs:enable
	}
}