Right, except:
create table test (a text, b int); create or replace rule test_rule as on insert to test where exists(select 1 from test where a = NEW.a) do instead select * from test;
insert into test (a,b) VALUES ('first',2); a | b -------+--- first | 2 (1 row)
select * from test; a | b -------+--- first | 2 (1 row)
Now, the select on the first insert should NOT have happened..... Since this is a do instead rule. The insert should of course happen, since it's not present in the table.
Or am I missing the point completely?
You are, but it's not your fault. You're still thinking of it as a sequence of instructions, try thinking of it as a single expression that gets evaluated.
To quote from the (v8.0) docs (ch 32 - The Rule System), for your case:
"Qualification given and INSTEAD
the query tree from the rule action with the rule qualification and the original query tree's qualification; and the original query tree with the negated rule qualification added"
So, in your case you get two branches: 1. INSERT ... WHERE NOT EXISTS (...) 2. SELECT * FROM TEST WHERE EXISTS (...)
Is this making sense? -- Richard Huxton Archonet Ltd
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