CREATE TABLE test(a INT, b VARCHAR(256), c INT, d VARCHAR(256), /* more fields follows*/); CREATE UNIQUE INDEX test_x( b, c, d );
Now I try to do:
INSERT INTO test VALUES( 0, 'abc', 12345, (SELECT foo FROM bar), /*more data follow*/);
My problem is:
The SELECT can either return data or NULL. Everything is good when the data is returned, but the insert fails when the NULL is returned, because the field "d" is a part of UNIQUE INDEX.
However,, I'd like to still insert the record and I'd like to do something like:
INSERT INTO test VALUES( 0, 'abc', 12345, IF( (SELECT foo FROM bar) == NULL, "postgres", <select_result>), /*more data follow*/);
"Specifies whether for a unique index, null values should be considered distinct (not equal). The default is that they are distinct, so that a unique index could contain multiple null values in a column."
That seems to mean multiple rows can have NULL in column "d".
It does work:
dba=# create table foo (a int, b int, c int, d int); CREATE TABLE dba=# create unique index i_foo_u1 on foo (a, b, d); CREATE INDEX dba=# dba=# insert into foo values (1, 1, 1, 1); INSERT 0 1 dba=# insert into foo values (2, 2, 2, null); INSERT 0 1 dba=# insert into foo values (3, 3, 3, null); INSERT 0 1 dba=# insert into foo values (4, 4, 4, null); INSERT 0 1
