问题
My query is as follow:
UPDATE t1 SET t1.foreign_key = (SELECT id FROM t2 WHERE t2.col = %s )
WHERE t1.col = %s
How do I return some attributes of the updated row in the table in the same query?
回答1:
Use the RETURNING clause.
The optional
RETURNING
clause causesUPDATE
to compute and return value(s) based on each row actually updated. Any expression using the table's columns, and/or columns of other tables mentioned inFROM
, can be computed. The new (post-update) values of the table's columns are used.
But typically it's smarter to use a join instead of a correlated subquery:
UPDATE t1
SET foreign_key = t2.id
FROM t2
WHERE t2.col = %s
AND t1.col = %s
RETURNING t1.*; -- or only selected columns
With your original query, if the subquery finds no row in t2
, t1
is updated anyway and t1.col
is set to NULL. Typically, you'd rather not update the row in this case, which is what my suggested query does instead.
BTW, target columns in the SET
clause cannot be table-qualified (only one table is updated anyway). The manual once more:
Do not include the table's name in the specification of a target column — for example,
UPDATE table_name SET table_name.col = 1
is invalid.
回答2:
You can use the RETURNING
clause:
UPDATE t1
SET t1.foreign_key = (SELECT id FROM t2 WHERE t2.col = %s )
WHERE t1.col = %s
RETURNING *;
The documentation is part of the UPDATE
statement.
来源:https://stackoverflow.com/questions/38948800/return-updated-row-attributes-on-update