Sql updating a table
clause; columns not explicitly modified retain their previous values.
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.
The sub-query can refer to old values of the current row of the table being updated.
In such case, I will perform join between target table and source table using join on customer ID.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;.You cannot restore data to a state corresponding to an earlier COMMIT.In a nutshell, these are the SQL rules regarding transaction control.