On Wed, Mar 22, 2023 at 4:32 PM Eske Rahn <e...@septima.dk> wrote: > Hi, > > Thanks for the quick answer *:-D* > > That was a nice sideeffect of lateral. > > In the example, the calling code also gets simplified: > > WITH x AS ( > SELECT clock_timestamp() rowstart, *, clock_timestamp() rowend FROM ( > SELECT '1' inp UNION > SELECT '2' > ) y, LATERAL septima.foo(inp) g > ) > SELECT * FROM x; > > > That solved the issue at hand, in a much better way. Thanks > > Though I still fail to see *why* the other way should generally call the > function for every column in the *result* record - if the function is > STABLE or IMMUTABLE. >
It gets rewritten to be effectively: select func_call(...).col1, func_call(...).col2, func_call(...).col3 under the assumption that repeating the function call will be cheap and side-effect free. It was never ideal but fixing that form of optimization was harder than implementing LATERAL where the multi-column result has a natural output in the form of a multi-column table. A normal function call in the target list really means "return a single value" which is at odds with writing .* after it. David J.
