distsqlrun: fix lookup join with limit

Previously, lookup join used its processRowHelper in an inappropriate place (not directly before returning a row) which caused the final rows in a limit query to get omitted in certain cases. Correct this problem. Release note (bug fix): lookup joins no longer omit rows in certain circumstances during limit queries.
cockroachdb · Oct 1, 2018 · 54cd53c · 54cd53c
1 parent d088e36
commit 54cd53c
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Showing 2 changed files with 29 additions and 9 deletions.
diff --git a/pkg/sql/distsqlrun/joinreader.go b/pkg/sql/distsqlrun/joinreader.go
@@ -501,11 +501,9 @@ func (jr *joinReader) performLookup() (joinReaderState, *ProducerMetadata) {
 				return jrStateUnknown, jr.DrainHelper()
 			}
 			if renderedRow != nil {
-				if row := jr.ProcessRowHelper(renderedRow); row != nil {
-					jr.toEmit = append(jr.toEmit, jr.out.rowAlloc.CopyRow(row))
-					if jr.emitted != nil {
-						jr.emitted[inputRowIdx] = true
-					}
+				jr.toEmit = append(jr.toEmit, jr.out.rowAlloc.CopyRow(renderedRow))
+				if jr.emitted != nil {
+					jr.emitted[inputRowIdx] = true
 				}
 			}
 		}
@@ -524,10 +522,8 @@ func (jr *joinReader) collectUnmatched() joinReaderState {
 	if jr.joinType == sqlbase.LeftOuterJoin {
 		for i := 0; i < len(jr.inputRows); i++ {
 			if !jr.emitted[i] {
-				if renderedRow := jr.renderUnmatchedRow(jr.inputRows[i], leftSide); renderedRow != nil {
-					if row := jr.ProcessRowHelper(renderedRow); row != nil {
-						jr.toEmit = append(jr.toEmit, jr.out.rowAlloc.CopyRow(row))
-					}
+				if row := jr.renderUnmatchedRow(jr.inputRows[i], leftSide); row != nil {
+					jr.toEmit = append(jr.toEmit, jr.out.rowAlloc.CopyRow(row))
 				}
 			}
 		}
@@ -551,6 +547,7 @@ func (jr *joinReader) emitRow() (joinReaderState, sqlbase.EncDatumRow, *Producer
 	}
 	row := jr.toEmit[0]
 	jr.toEmit = jr.toEmit[1:]
+	row = jr.ProcessRowHelper(row)
 	return jrEmittingRows, row, nil
 }
 

diff --git a/pkg/sql/logictest/testdata/logic_test/distsql_lookup_join b/pkg/sql/logictest/testdata/logic_test/distsql_lookup_join
@@ -355,3 +355,26 @@ SELECT t1.c, t2.d FROM multiples t1 LEFT JOIN multiples@bc t2 ON t1.c = t2.b WHE
 ----
 6   12
 12  24
+
+# Regression test for #30812: make sure that lookup joins with limit don't
+# omit the final row.
+
+statement ok
+CREATE TABLE t_30182_l (id INT PRIMARY KEY, name TEXT NOT NULL)
+
+statement ok
+CREATE TABLE t_30182_r (id INT PRIMARY KEY, name TEXT NOT NULL, l_id int)
+
+statement ok
+INSERT INTO t_30182_l (id, name) values(1, 'a')
+
+statement ok
+INSERT INTO t_30182_r values(1, 'foo', 1);
+
+query ITI
+SELECT r.* FROM t_30182_r r
+JOIN t_30182_l l on r.l_id = l.id
+WHERE r.name = 'foo'
+LIMIT 1
+----
+1 foo 1