The individual statement probes are provided to give specific information about different statement
types. For the start probes the string of the query is provided as a the only argument. Depending on
the statement type, the information provided by the corresponding done probe will differ. For all done
probes the status of the operation (0 for success, 0 for failure) is provided. For SELECT, INSERT,
INSERT ... (SELECT FROM ...), DELETE, and DELETE FROM t1,t2 operations the number of
rows affected is returned.
For UPDATE and UPDATE t1,t2 ... statements the number of rows matched and the number
of rows actually changed is provided. This is because the number of rows actually matched by the
corresponding WHERE clause, and the number of rows changed can differ. MySQL does not update the
value of a row if the value already matches the new setting.
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