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Commit8f4ee96

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Fix Assert failure in WITH RECURSIVE UNION queries
If the non-recursive part of a recursive CTE ended up usingTTSOpsBufferHeapTuple as the table slot type, then a duplicate valuecould cause an Assert failure in CheckOpSlotCompatibility() whenchecking the hash table for the duplicate value. The expected slot typefor the deform step was TTSOpsMinimalTuple so the Assert failed when theTTSOpsBufferHeapTuple slot was used.This is a long-standing bug which we likely didn't notice because itseems much more likely that the non-recursive term would have requiredprojection and used a TTSOpsVirtual slot, which CheckOpSlotCompatibilityis ok with.There doesn't seem to be any harm done here other than the Assertfailure. Both TTSOpsMinimalTuple and TTSOpsBufferHeapTuple slot typesrequire tuple deformation, so the EEOP_*_FETCHSOME ExprState step wouldhave properly existed in the ExprState.The solution is to pass NULL for the ExecBuildGroupingEqual's 'lops'parameter. This means the ExprState's EEOP_*_FETCHSOME step won'texpect a fixed slot type. This makes CheckOpSlotCompatibility() happy asno checking is performed when the ExprEvalStep is not expecting a fixedslot type.Reported-by: Richard GuoReviewed-by: Tom LaneDiscussion:https://postgr.es/m/CAMbWs4-8U9q2LAtf8+ghV11zeUReA3AmrYkxzBEv0vKnDxwkKA@mail.gmail.comBackpatch-through: 13, all supported versions
1 parentb7493e1 commit8f4ee96

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3 files changed

+28
-2
lines changed

3 files changed

+28
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lines changed

‎src/backend/executor/execGrouping.c

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@@ -236,9 +236,8 @@ BuildTupleHashTableExt(PlanState *parent,
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hash_iv);
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/* build comparator for all columns */
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/* XXX: should we support non-minimal tuples for the inputslot? */
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hashtable->tab_eq_func=ExecBuildGroupingEqual(inputDesc,inputDesc,
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&TTSOpsMinimalTuple,&TTSOpsMinimalTuple,
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NULL,&TTSOpsMinimalTuple,
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numCols,
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keyColIdx,eqfuncoids,collations,
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allow_jit ?parent :NULL);

‎src/test/regress/expected/with.out

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Original file line numberDiff line numberDiff line change
@@ -656,6 +656,21 @@ SELECT t1.id, t2.path, t2 FROM t AS t1 JOIN t AS t2 ON
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16 | {3,7,11,16} | (16,"{3,7,11,16}")
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(16 rows)
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CREATE TEMP TABLE duplicates (a INT NOT NULL);
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INSERT INTO duplicates VALUES(1), (1);
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-- Try out a recursive UNION case where the non-recursive part's table slot
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-- uses TTSOpsBufferHeapTuple and contains duplicate rows.
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WITH RECURSIVE cte (a) as (
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SELECT a FROM duplicates
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UNION
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SELECT a FROM cte
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)
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SELECT a FROM cte;
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a
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---
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1
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(1 row)
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-- test that column statistics from a materialized CTE are available
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-- to upper planner (otherwise, we'd get a stupider plan)
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explain (costs off)

‎src/test/regress/sql/with.sql

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -361,6 +361,18 @@ UNION ALL
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SELECTt1.id,t2.path, t2FROM tAS t1JOIN tAS t2ON
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(t1.id=t2.id);
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CREATE TEMP TABLE duplicates (aINTNOT NULL);
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INSERT INTO duplicatesVALUES(1), (1);
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-- Try out a recursive UNION case where the non-recursive part's table slot
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-- uses TTSOpsBufferHeapTuple and contains duplicate rows.
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WITH RECURSIVE cte (a)as (
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SELECT aFROM duplicates
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UNION
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SELECT aFROM cte
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)
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SELECT aFROM cte;
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-- test that column statistics from a materialized CTE are available
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-- to upper planner (otherwise, we'd get a stupider plan)
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explain (costs off)

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