maybe_convert_table_to_utf8mb4( string $table ): bool

Source

 * If a table only contains utf8 or utf8mb4 columns, convert it to utf8mb4.
 *
 * @since 4.2.0
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $table The table to convert.
 * @return bool True if the table was converted, false if it wasn't.
 */
function maybe_convert_table_to_utf8mb4( $table ) {
	global $wpdb;

	$results = $wpdb->get_results( "SHOW FULL COLUMNS FROM `$table`" );
	if ( ! $results ) {
		return false;
	}

	foreach ( $results as $column ) {
		if ( $column->Collation ) {
			list( $charset ) = explode( '_', $column->Collation );
			$charset         = strtolower( $charset );
			if ( 'utf8' !== $charset && 'utf8mb4' !== $charset ) {
				// Don't upgrade tables that have non-utf8 columns.
				return false;
			}
		}
	}

	$table_details = $wpdb->get_row( "SHOW TABLE STATUS LIKE '$table'" );
	if ( ! $table_details ) {
		return false;
	}

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