ordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare -- $source_meta_rel_id_column, $source_destination_rel_id_column etc is escaped for backticks. $where clause and $order_by should already be escaped.
		$query = $wpdb->prepare(
			"
SELECT
	$source_meta_rel_id_column as entity_meta_rel_id,
    $source_primary_key_column as primary_key_id,
	$entity_column_string
FROM `$source_entity_table`
WHERE $where_clause;
",
			$entity_ids
		);

		// phpcs:enable

		return $query;
	}

	/**
	 * Helper method to build query that will be used to fetch data from source meta table.
	 *
	 * @param array $entity_ids List of IDs to fetch metadata for.
	 *
	 * @return string Query for fetching meta data.
	 */
	private function build_meta_data_query( array $entity_ids ): string {
		global $wpdb;

		$meta_table                = $this->schema_config['source']['meta']['table_name'];
		$meta_keys                 = array_keys( $this->meta_column_mapping );
		$meta_key_column           = $this->schema_config['source']['meta']['meta_key_column'];
		$meta_value_column         = $this->schema_config['source']['meta']['meta_value_column'];
		$meta_table_relational_key = $this->schema_config['source']['meta']['entity_id_column'];

		$meta_column_string = implode( ', ', array_fill( 0, count( $meta_keys ), '%s' ) );
		$entity_id_string   = implode( ', ', array_fill( 0, count( $entity_ids ), '%d' ) );

		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare -- $meta_table_relational_key, $meta_key_column, $meta_value_column and $meta_table is escaped for backticks. $entity_id_string and $meta_column_string are placeholders.
		$query = $wpdb->prepare(
			"
SELECT `$meta_table_relational_key` as entity_id, `$meta_key_column` as meta_key, `$meta_value_column` as meta_value
FROM `$meta_table`
WHERE
	`$meta_table_relational_key` IN ( $entity_id_string )
	AND `$meta_key_column` IN ( $meta_column_string );
",
			array_merge(
				$entity_ids,
				$meta_keys
			)
		);

		// phpcs:enable

		return $query;
	}

	/**
	 * Helper function to validate and combine data before we try to insert.
	 *
	 * @param array $entity_data Data from source table.
	 * @param array $meta_data Data from meta table.
	 *
	 * @return array[] Validated and combined data with errors.
	 */
	private function process_and_sanitize_data( array $entity_data, array $meta_data ): array {
		$sanitized_entity_data = array();
		$error_records         = array();
		$this->process_and_sanitize_entity_data( $sanitized_entity_data, $error_records, $entity_data );
		$this->processs_and_sanitize_meta_data( $sanitized_entity_data, $error_records, $meta_data );

		return array(
			'data'   => $sanitized_entity_data,
			'errors' => $error_records,
		);
	}

	/**
	 * Helper method to sanitize core source table.
	 *
	 * @param array $sanitized_entity_data Array containing sanitized data for insertion.
	 * @param array $error_records Error records.
	 * @param array $entity_data Original source data.
	 */
	private function process_and_sanitize_entity_data( array &$sanitized_entity_data, array &$error_records, array $entity_data ): void {
		foreach ( $entity_data as $entity ) {
			$row_data = array();
			foreach ( $this->core_column_mapping as $column_name => $schema ) {
				$custom_table_column_name = $schema['destination'] ?? $column_name;
				$value                    = $entity->$column_name;
				$value                    = $this->validate_data( $value, $schema['type'] );
				if ( is_wp_error( $value ) ) {
					$error_records[ $entity->primary_key_id ][ $custom_table_column_name ] = $value->get_error_code();
				} else {
					$row_data[ $custom_table_column_name ] = $value;
				}
			}
			$sanitized_entity_data[ $entity->entity_meta_rel_id ] = $row_data;
		}
	}

	/**
	 * Helper method to sanitize soure meta data.
	 *
	 * @param array $sanitized_entity_data Array containing sanitized data for insertion.
	 * @param array $error_records Error records.
	 * @param array $meta_data Original source data.
	 */
	private function processs_and_sanitize_meta_data( array &$sanitized_entity_data, array &$error_records, array $meta_data ): void {
		foreach ( $meta_data as $datum ) {
			$column_schema = $this->meta_column_mapping[ $datum->meta_key ];
			if ( isset( $sanitized_entity_data[ $datum->entity_id ][ $column_schema['destination'] ] ) ) {
				// We pick only the first meta if there are duplicates for a flat column, to be consistent with WP core behavior in handing duplicate meta which are marked as unique.
				continue;
			}
			$value = $this->validate_data( $datum->meta_value, $column_schema['type'] );
			if ( is_wp_error( $value ) ) {
				$error_records[ $datum->entity_id ][ $column_schema['destination'] ] = "{$value->get_error_code()}: {$value->get_error_message()}";
			} else {
				$sanitized_entity_data[ $datum->entity_id ][ $column_schema['destination'] ] = $value;
			}
		}
	}

	/**
	 * Validate and transform data so that we catch as many errors as possible before inserting.
	 *
	 * @param mixed  $value Actual data value.
	 * @param string $type Type of data, could be decimal, int, date, string.
	 *
	 * @return float|int|mixed|string|\WP_Error
	 */
	private function validate_data( $value, string $type ) {
		switch ( $type ) {
			case 'decimal':
				$value = wc_format_decimal( floatval( $value ), false, true );
				break;
			case 'int':
				$value = (int) $value;
				break;
			case 'bool':
				$value = wc_string_to_bool( $value );
				break;
			case 'date':
				try {
					if ( '' === $value ) {
						$value = null;
					} else {
						$value = ( new \DateTime( $value ) )->format( 'Y-m-d H:i:s' );
					}
				} catch ( \Exception $e ) {
					return new \WP_Error( $e->getMessage() );
				}
				break;
			case 'date_epoch':
				try {
					if ( '' === $value ) {
						$value = null;
					} else {
						$value = ( new \DateTime( "@$value" ) )->format( 'Y-m-d H:i:s' );
					}
				} catch ( \Exception $e ) {
					return new \WP_Error( $e->getMessage() );
				}
				break;
		}

		return $value;
	}

	/**
	 * Verify whether data was migrated properly for given IDs.
	 *
	 * @param array $source_ids List of source IDs.
	 *
	 * @return array List of IDs along with columns that failed to migrate.
	 */
	public function verify_migrated_data( array $source_ids ) : array {
		global $wpdb;
		$query = $this->build_verification_query( $source_ids );
		// phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared -- $query should already be prepared.
		$results = $wpdb->get_results( $query, ARRAY_A );
		$results = $this->fill_source_metadata( $results, $source_ids );
		return $this->verify_data( $results );
	}

	/**
	 * Generate query to fetch data from both source and destination tables. Use the results in `verify_data` to verify if data was migrated properly.
	 *
	 * @param array $source_ids Array of IDs in source table.
	 *
	 * @return string SELECT statement.
	 */
	protected function build_verification_query( $source_ids ) {
		$source_table                  = $this->schema_config['source']['entity']['table_name'];
		$destination_table             = $this->schema_config['destination']['table_name'];
		$destination_source_rel_column = $this->schema_config['destination']['source_rel_column'];
		$source_destination_rel_column = $this->schema_config['source']['entity']['destination_rel_column'];

		$source_destination_join_clause = "$destination_table ON $destination_table.$destination_source_rel_column = $source_table.$source_destination_rel_column";

		$meta_select_clauses        = array();
		$source_select_clauses      = array();
		$destination_select_clauses = array();

		foreach ( $this->core_column_mapping as $column_name => $schema ) {
			$source_select_column         = isset( $schema['select_clause'] ) ? $schema['select_clause'] : "$source_table.$column_name";
			$source_select_clauses[]      = "$source_select_column as {$source_table}_{$column_name}";
			$destination_select_clauses[] = "$destination_table.{$schema['destination']} as {$destination_table}_{$schema['destination']}";
		}

		foreach ( $this->meta_column_mapping as $meta_key => $schema ) {
			$destination_select_clauses[] = "$destination_table.{$schema['destination']} as {$destination_table}_{$schema['destination']}";
		}

		$select_clause = implode( ', ', array_merge( $source_select_clauses, $meta_select_clauses, $destination_select_clauses ) );

		$where_clause = $this->get_where_clause_for_verification( $source_ids );

		return "
SELECT $select_clause
FROM $source_table
    LEFT JOIN $source_destination_join_clause
WHERE $where_clause
";
	}

	/**
	 * Fill source metadata for given IDs for verification. This will return filled data in following format:
	 * [
	 *    {
	 *      $source_table_$source_column: $value,
	 *      ...,
	 *      $destination_table_$destination_column: $value,
	 *      ...
	 *      meta_source_{$destination_column_name1}: $meta_value,
	 *      ...
	 *    },
	 *   ...
	 * ]
	 *
	 * @param array $results    Entity data from both source and destination table.
	 * @param array $source_ids List of source IDs.
	 *
	 * @return array Filled $results param with source metadata.
	 */
	private function fill_source_metadata( $results, $source_ids ) {
		global $wpdb;
		$meta_table            = $this->schema_config['source']['meta']['table_name'];
		$meta_entity_id_column = $this->schema_config['source']['meta']['entity_id_column'];
		$meta_key_column       = $this->schema_config['source']['meta']['meta_key_column'];
		$meta_value_column     = $this->schema_config['source']['meta']['meta_value_column'];
		$meta_id_column        = $this->schema_config['source']['meta']['meta_id_column'];
		$meta_columns          = array_keys( $this->meta_column_mapping );

		$meta_columns_placeholder = implode( ', ', array_fill( 0, count( $meta_columns ), '%s' ) );
		$source_ids_placeholder   = implode( ', ', array_fill( 0, count( $source_ids ), '%d' ) );

		$query = $wpdb->prepare(
		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
			"SELECT $meta_entity_id_column as entity_id, $meta_key_column as meta_key, $meta_value_column as meta_value
			FROM $meta_table
			WHERE $meta_entity_id_column IN ($source_ids_placeholder)
			AND $meta_key_column IN ($meta_columns_placeholder)
			ORDER BY $meta_id_column ASC",
			array_merge( $source_ids, $meta_columns )
		);
		//phpcs:enable

		// phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
		$meta_data            = $wpdb->get_results( $query, ARRAY_A );
		$source_metadata_rows = array();
		foreach ( $meta_data as $meta_datum ) {
			if ( ! isset( $source_metadata_rows[ $meta_datum['entity_id'] ] ) ) {
				$source_metadata_rows[ $meta_datum['entity_id'] ] = array();
			}
			$destination_column = $this->meta_column_mapping[ $meta_datum['meta_key'] ]['destination'];
			$alias              = "meta_source_{$destination_column}";
			if ( isset( $source_metadata_rows[ $meta_datum['entity_id'] ][ $alias ] ) ) {
				// Only process first value, duplicate values mapping to flat columns are ignored to be consistent with WP core.
				continue;
			}
			$source_metadata_rows[ $meta_datum['entity_id'] ][ $alias ] = $meta_datum['meta_value'];
		}
		foreach ( $results as $index => $result_row ) {
			$source_id         = $result_row[ $this->schema_config['source']['entity']['table_name'] . '_' . $this->schema_config['source']['entity']['primary_key'] ];
			$results[ $index ] = array_merge( $result_row, ( $source_metadata_rows[ $source_id ] ?? array() ) );
		}
		return $results;
	}

	/**
	 * Helper function to generate where clause for fetching data for verification.
	 *
	 * @param array $source_ids Array of IDs from source table.
	 *
	 * @return string WHERE clause.
	 */
	protected function get_where_clause_for_verification( $source_ids ) {
		global $wpdb;
		$source_primary_id_column = $this->schema_config['source']['entity']['primary_key'];
		$source_table             = $this->schema_config['source']['entity']['table_name'];
		$source_ids_placeholder   = implode( ', ', array_fill( 0, count( $source_ids ), '%d' ) );

		return $wpdb->prepare(
			// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
			"$source_table.$source_primary_id_column IN ($source_ids_placeholder)",
			$source_ids
		);
	}

	/**
	 * Verify data from both source and destination tables and check if they were migrated properly.
	 *
	 * @param array $collected_data Collected data in array format, should be in same structure as returned from query in `$this->build_verification_query`.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	protected function verify_data( $collected_data ) {
		$failed_ids = array();
		foreach ( $collected_data as $row ) {
			$failed_ids = $this->verify_entity_columns( $row, $failed_ids );
			$failed_ids = $this->verify_meta_columns( $row, $failed_ids );
		}

		return $failed_ids;
	}

	/**
	 * Helper method to verify and compare core columns.
	 *
	 * @param array $row        Both migrated and source data for a single row.
	 * @param array $failed_ids Array of failed IDs.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	private function verify_entity_columns( $row, $failed_ids ) {
		$primary_key_column = "{$this->schema_config['source']['entity']['table_name']}_{$this->schema_config['source']['entity']['primary_key']}";
		foreach ( $this->core_column_mapping as $column_name => $schema ) {
			$source_alias      = "{$this->schema_config['source']['entity']['table_name']}_$column_name";
			$destination_alias = "{$this->schema_config['destination']['table_name']}_{$schema['destination']}";
			$row               = $this->pre_process_row( $row, $schema, $source_alias, $destination_alias );
			if ( $row[ $source_alias ] !== $row[ $destination_alias ] ) {
				if ( ! isset( $failed_ids[ $row[ $primary_key_column ] ] ) ) {
					$failed_ids[ $row[ $primary_key_column ] ] = array();
				}
				$failed_ids[ $row[ $primary_key_column ] ][] = array(
					'column'         => $column_name,
					'original_value' => $row[ $source_alias ],
					'new_value'      => $row[ $destination_alias ],
				);
			}
		}

		return $failed_ids;
	}

	/**
	 * Helper method to verify meta columns.
	 *
	 * @param array $row        Both migrated and source data for a single row.
	 * @param array $failed_ids Array of failed IDs.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	private function verify_meta_columns( $row, $failed_ids ) {
		$primary_key_column = "{$this->schema_config['source']['entity']['table_name']}_{$this->schema_config['source']['entity']['primary_key']}";
		foreach ( $this->meta_column_mapping as $meta_key => $schema ) {
			$meta_alias        = "meta_source_{$schema['destination']}";
			$destination_alias = "{$this->schema_config['destination']['table_name']}_{$schema['destination']}";
			$row               = $this->pre_process_row( $row, $schema, $meta_alias, $destination_alias );
			if ( $row[ $meta_alias ] !== $row[ $destination_alias ] ) {
				if ( ! isset( $failed_ids[ $row[ $primary_key_column ] ] ) ) {
					$failed_ids[ $row[ $primary_key_column ] ] = array();
				}
				$failed_ids[ $row[ $primary_key_column ] ][] = array(
					'column'         => $meta_key,
					'original_value' => $row[ $meta_alias ],
					'new_value'      => $row[ $destination_alias ],
				);
			}
		}

		return $failed_ids;
	}

	/**
	 * Helper method to pre-process rows to make sure we parse the correct type.
	 *
	 * @param array  $row Both migrated and source data for a single row.
	 * @param array  $schema Column schema.
	 * @param string $alias Name of source column.
	 * @param string $destination_alias Name of destination column.
	 *
	 * @return array Processed row.
	 */
	private function pre_process_row( $row, $schema, $alias, $destination_alias ) {
		if ( ! isset( $row[ $alias ] ) ) {
			$row[ $alias ] = $this->get_type_defaults( $schema['type'] );
		}
		if ( is_null( $row[ $destination_alias ] ) ) {
			$row[ $destination_alias ] = $this->get_type_defaults( $schema['type'] );
		}
		if ( in_array( $schema['type'], array( 'int', 'decimal', 'float' ), true ) ) {
			if ( '' === $row[ $alias ] || null === $row[ $alias ] ) {
				$row[ $alias ] = 0; // $wpdb->prepare forces empty values to 0.
			}
			$row[ $alias ]             = wc_format_decimal( floatval( $row[ $alias ] ), false, true );
			$row[ $destination_alias ] = wc_format_decimal( floatval( $row[ $destination_alias ] ), false, true );
		}
		if ( 'bool' === $schema['type'] ) {
			$row[ $alias ]             = wc_string_to_bool( $row[ $alias ] );
			$row[ $destination_alias ] = wc_string_to_bool( $row[ $destination_alias ] );
		}
		if ( 'date_epoch' === $schema['type'] ) {
			if ( '' === $row[ $alias ] || null === $row[ $alias ] ) {
				$row[ $alias ] = null;
			} else {
				$row[ $alias ] = ( new \DateTime( "@{$row[ $alias ]}" ) )->format( 'Y-m-d H:i:s' );
			}
			if ( '0000-00-00 00:00:00' === $row[ $destination_alias ] ) {
				$row[ $destination_alias ] = null;
			}
		}
		return $row;
	}

	/**
	 * Helper method to get default value of a type.
	 *
	 * @param string $type Type.
	 *
	 * @return mixed Default value.
	 */
	private function get_type_defaults( $type ) {
		switch ( $type ) {
			case 'float':
			case 'int':
			case 'decimal':
				return 0;
			case 'string':
				return '';
		}
	}
}