Is `Delete From Join` Standard SQL?

Question

Among other questions, this one asked how to delete from a join.

My question: How much of this is standard SQL? On which databases would this actually work (most notably for me would be Oracle, MySQL and SQLServer)?

Answer 1

Not standard according to International Standard ISO/IEC 9075:1992 Section 13.6, pages 384-386. Delete with JOIN syntax won't work in Oracle.

Answer 2

DELETE ... FROM .. Is not part of the ANSI standards, nor UPDATE ... FROM ... for that matter. This includes any join syntax, since the join can only be specified with a FROM.

All vendors implement this though in one form or another.

Answer 3

this will actually work in Oracle. The FROM keyword is optional: DELETE (query) is the same as DELETE FROM (query).

The rules to DELETE a JOIN are the same as the rules to update a JOIN: Oracle will modify the rows from only one table and only if there is no ambiguity in identifying the rows of the base table. Look in this SO or this SO for example.

Let's build a small example:

CREATE TABLE t_parent (ID NUMBER PRIMARY KEY, NAME VARCHAR2(10));
CREATE TABLE t_child (ID NUMBER PRIMARY KEY, 
                      parent_id NUMBER REFERENCES t_parent);
INSERT INTO t_parent VALUES (1, 'a');
INSERT INTO t_child VALUES (1, 1);
INSERT INTO t_child VALUES (2, 1);

You can delete rows from the CHILD table:

SQL> DELETE FROM (SELECT t_child.*
  2                 FROM t_child
  3                 JOIN t_parent ON t_parent.id = t_child.parent_id
  4                WHERE t_parent.name = 'a');

2 rows deleted