Restore lazy evaluation of fallible CASE #15390
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findepi merged 2 commits intoapache:mainfrom Mar 25, 2025
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Alternatively, we could change |
Commit 0f4b8b1 introduced a new optimized evaluation mode for CASE expression with exactly one WHEN-THEN clause and ELSE clause being present. Apparently, the new mode did not take into account expensive or fallible expressions, as it unconditionally evaluated both branches. This is definitely incorrect for fallible expressions. For these, fallback to the original execution mode.
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alamb
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Thank you @findepi
Given the code was generating incorrect answers but is now correct this looks good to me. I am running some benchmarks to see if there are any performance impacts
cc @aweltsch @2010YOUY01 who authored/helped with #13953
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| query II |
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I verified that this errors on main:
> SELECT v, CASE WHEN v != 0 THEN 10/v ELSE 42 END FROM (VALUES (0), (1), (2)) t(v);
+---+-------------------------------------------------------------------+
| v | CASE WHEN t.v != Int64(0) THEN Int64(10) / t.v ELSE Int64(42) END |
+---+-------------------------------------------------------------------+
| 0 | 42 |
| 1 | 10 |
| 2 | 5 |
+---+-------------------------------------------------------------------+
3 row(s) fetched.
Elapsed 0.002 seconds.
> SELECT v, CASE WHEN v < 0 THEN 10/0 ELSE 1 END FROM (VALUES (1), (2)) t(v);
Arrow error: Divide by zero error
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Here are my benchmark results. My conclusion is no discernable difference |
qstommyshu
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Mar 27, 2025
* Restore lazy evaluation of fallible CASE Commit 0f4b8b1 introduced a new optimized evaluation mode for CASE expression with exactly one WHEN-THEN clause and ELSE clause being present. Apparently, the new mode did not take into account expensive or fallible expressions, as it unconditionally evaluated both branches. This is definitely incorrect for fallible expressions. For these, fallback to the original execution mode. * Workaround for running sqllogictests in RustRover
nirnayroy
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* Restore lazy evaluation of fallible CASE Commit 0f4b8b1 introduced a new optimized evaluation mode for CASE expression with exactly one WHEN-THEN clause and ELSE clause being present. Apparently, the new mode did not take into account expensive or fallible expressions, as it unconditionally evaluated both branches. This is definitely incorrect for fallible expressions. For these, fallback to the original execution mode. * Workaround for running sqllogictests in RustRover
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Which issue does this PR close?
Rationale for this change
Commit 0f4b8b1 (#13953) introduced a new
optimized evaluation mode for CASE expression with exactly one WHEN-THEN
clause and ELSE clause being present. Apparently, the new mode did not
take into account expensive or fallible expressions, as it
unconditionally evaluated both branches. This is definitely incorrect
for fallible expressions. For these, fallback to the original execution
mode.
What changes are included in this PR?
fix so that CASE is lazy again
Are these changes tested?
slt
Are there any user-facing changes?
yes