![]() Or why it's there there is plenty of dialogue on the hacker list and commit logs to keep you entertained. One thing I love about PostgreSQL that you miss with closed-source and even with other open source projects, is that when you are curious about a new feature > Function Scan on pg_catalog.generate_series i (cost=0.00.10.00 rows=1000 width=0) Good old backwards compatible way: SELECT count(*)įROM (SELECT CASE i WHEN 1 THEN 'First' ELSE 'Not First' ENDįROM generate_series(1,10000000) AS i) AS f Aggregate (cost=12.50.12.51 rows=1 width=8) Output: CASE (generate_series(1, 10000000)) WHEN 1 THEN 'First'::text ELSE 'Not First'::text END Uses this new thing called a ProjectSet executor and takes ~1 second Aggregate (cost=32.52.32.53 rows=1 width=8) (actual time=1036.048.1036.048 rows=1 loops=1) Here is a quick test I did to compare the results and timing:įROM (SELECT CASE generate_series(1,10000000) WHEN 1 THEN 'First' ELSE 'Not First' END) AS f It should be noted though that, the new approach if you wanted to do something kinda crazy like that does seem to be faster than the standard approach. But that's still beingĭiscussed, and the code would reside in places not touched here, so that's ![]() Likely to instead prohibit SRFs in those places. That's because the SRFs areĮvaluated in a separate ProjectSet node. "arm" of the expression is not evaluated. Returning multiple rows from the expression, even when the SRF containing Not because it's particularlyĭesirable, but because it ends up working and there seems to be no argumentĬurrently the behavior for COALESCE and CASE containing SRFs has changed, That it's a side effect of other optimizations and introduction of new ProjectSet executor node.Īs a side effect, the previously prohibited case of multiple set returningĪrguments to a function, is now allowed. 172 7K views 3 years ago Curso de PostgreSQL APRENDE a USAR esta BASE de DATOS desde CERO Aprendemos a cmo usar el condicional CASE en un Select para crear una columna donde lo que diga. The answer seems reading from the commit notes, Why would I ever do that instead of something like this which will work in all versions? SELECT CASE i WHEN 1 THEN 'First' ELSE 'Not First' END Interesting, right, but how is this useful? In PostgreSQL 9.6 and below, you are slapped with an error message: ERROR: set-valued function called in context that cannot accept a set generate_series with CASE WHEN SELECT CASE generate_series(1,10) WHEN 1 THEN 'First' ELSE 'Not First' END If it's not for some reason to do with SQL's deeper architecture, I'd like to understand why.Since this article was written, this feature has been removed, because it caused old logic that had sets from doing something different without warning. This feels like a more correct & less wasteful way to do it. In the past I've done operations like this by doing two SELECTS, one of which is against the item_templates table, the other against the unique_items table, and taken their UNION. ![]() Or if this is something you can't do conceptually - have each row choose its own join - I'd love to get a link to a deeper explanation. If there's a quick fix for the syntax, I'd love to hear it. This is the sort of thing I've been trying, without success: SELECT item_table, item_id, * So when I find a record of an item in the item_instances table, I want to look up more information about it, and I need to pull that info from the correct table. They are now stored in the unique_items table. Say I've got a table of item_instances in my game, of all the items in the game world, and some of the items are cookie-cutter copies of generic items from the item_templates table, and other items started off as templates, and then acquired unique properties as players used them. I'm attempting to use a CASE expression to select which table each row should be joined with. ![]()
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