Updating a select statement to update
If the item already exists, instead update the stock count of the existing item.
To do this without failing the entire transaction, use savepoints: BEGIN; -- other operations SAVEPOINT sp1; INSERT INTO wines VALUES('Chateau Lafite 2003', '24'); -- Assume the above fails because of a unique key violation, -- so now we issue these commands: ROLLBACK TO sp1; UPDATE wines SET stock = stock 24 WHERE winename = 'Chateau Lafite 2003'; -- continue with other operations, and eventually COMMIT;.
If you access a column from the table to be updated in an expression, assignments are generally evaluated from left to right.
For multiple-table updates, there is no guarantee that assignments are carried out in any particular order. COLUMN2 IS NULLAn outerjoin is performed based on the equijoin condition.
There are two ways to modify a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the sub-query that produces as many output columns as are listed in the parenthesized column list preceding it.If you set a column to the value it currently has, My SQL notices this and does not update it. Records not matching the equijoin from table2 are marked with null.If you update a column that has been declared , an error occurs if strict SQL mode is enabled; otherwise, the column is set to the implicit default value for the column data type and the warning count is incremented. This facilitates to update table1 column with expression whose corresponding value from table2 is returned as NULL It took me a few minutes to figure this out, but the syntax for UPDATING ONE TABLE ONLY using a relationship between two tables in My SQL 4.0 is actually quite simple:update t1, t2 set t1.field = t2.value where t1= t2.that; It should be noted that even simple applications of UPDATE can conflict with the 'safe mode' setting of the mysql daemon.This option takes a list of one or more partitions or subpartitions (or both).