UPDATE/DELETE in mysql and get the list of affected row ids?
Is there an efficient way to get the list of affected row IDs (not the # of affected rows via PHP's mysql_affected_rows(), but the actual row ids that were affected) from an UPDATE or DELETE query in mysql?
In postgresql, there is a RETURNING clause within UPDATE/DELETE queries that can be used to specify values from the affected rows that are returned.
In mysql, the 'brute force' way of getting the affected rows seem to be: 1. Acquire READ LOCK. 2. SELECT to with the WHERE condition of the UPDATE/DELETE query to get the affected row ids. 3. UPDATE/DELETE. 4. RELEASE LOCK.
The above way seems very inefficient. Is there a more efficient way to get the affected row ids in mysql?
Answer
You can create a Trigger
Support for triggers is included beginning with MySQL 5.0.2. A trigger is a named database object that is associated with a table, and that activates when a particular event occurs for the table.
the following code creates a trigger on a table named mytable which has a field id
CREATE TRIGGER mytable_delete
AFTER DELETE ON mytable
FOR EACH ROW SET @deletedIDs = CONCAT_WS(',', @deletedIDs, OLD.id)
notice that OLD refers to deleted row
once you created a trigger on a table you can use it as follows:
/* empty parameter defined in CREATE TRIGGER */
Set @deletedIDs = '';
/* perform your query */
DELETE FROM mytable WHERE myotherfield = 'myfilterevalue';
/* get the parameter */
SELECT @deletedIDs AS 'Deleted_IDs';
this will return deleted IDs each preceded by a comma in a string