Merge cockroachdb#105931

105931: colexec: don't infinite loop cross-join with zero-column left input r=DrewKimball a=DrewKimball

Previously, the cross-joiner wouldn't advance its internal state when its left input projected no columns. This would result in an infinite loop as the right rows were repeatedly emitted. This patch advances the state when there are no left columns as if values from the left side were emitted.

Fixes cockroachdb#105882

Release note (bug fix): Fixed a bug introduced in v22.1 that could cause a join to infinite-loop in rare cases when (1) the join filter is not an equality and (2) no columns from the left input are returned.

Co-authored-by: Drew Kimball <[email protected]>

Author: craig[bot]

pkg/sql/colexec/colexecjoin/crossjoiner.eg.go

@@ -168,6 +168,32 @@ func buildFromLeftBatch(b *crossJoinerBase, currentBatch coldata.Batch, sel []in
 			colexecerror.InternalError(errors.AssertionFailedf("unhandled type %s", b.left.types[colIdx].String()))
 		}
 	}
+	// If there are no columns projected from the left input, simply advance the
+	// cross-joiner state according to the number of input rows.
+	if len(b.left.types) == 0 {
+		outStartIdx := destStartIdx
+		for bs.curSrcStartIdx < leftSrcEndIdx && outStartIdx < outputCapacity {
+			// Repeat each row leftNumRepeats times.
+			// {{/* toAppend will always be positive. */}}
+			toAppend := leftNumRepeats - bs.numRepeatsIdx
+			if outStartIdx+toAppend > outputCapacity {
+				// We don't have enough space to repeat the current
+				// value the required number of times, so we'll have
+				// to continue from here on the next call.
+				toAppend = outputCapacity - outStartIdx
+				bs.numRepeatsIdx += toAppend
+			} else {
+				// We fully processed the current tuple for the
+				// current column, and before moving on to the next
+				// one, we need to reset numRepeatsIdx (so that the
+				// next tuple would be repeated leftNumRepeats
+				// times).
+				bs.curSrcStartIdx++
+				bs.numRepeatsIdx = 0
+			}
+			outStartIdx += toAppend
+		}
+	}
 }
 
 // buildFromLeftInput builds part of the output of a cross join that comes from

pkg/sql/colexec/colexecjoin/crossjoiner_tmpl.go

@@ -81,3 +81,18 @@ SELECT *
        )
  WHERE r < .01
  LIMIT 1
+
+# Regression test for #105882 - don't infinite loop when the left input has
+# no columns.
+statement ok
+CREATE TABLE t105882 (c0 INT);
+UPSERT INTO t105882 (c0) VALUES(1);
+
+query I
+SELECT (
+  SELECT count(t2.rowid) FROM t105882 t2
+  WHERE ((t1.rowid) IN (SELECT max(t3.rowid) FROM t105882 t3))
+)
+FROM t105882 t1;
+----
+1