executor: fix group_concat(a) when a is null (#7287)

pingcap · Aug 8, 2018 · af7fed9 · af7fed9
1 parent b39b5f5
commit af7fed9
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Showing 2 changed files with 19 additions and 3 deletions.
diff --git a/executor/aggfuncs/func_group_concat.go b/executor/aggfuncs/func_group_concat.go
@@ -103,8 +103,11 @@ func (e *groupConcat) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup [
 			p.buffer.WriteString(e.sep)
 		}
 	}
-	p.buffer.Truncate(p.buffer.Len() - len(e.sep))
-	return e.truncatePartialResultIfNeed(sctx, p.buffer)
+	if p.buffer != nil {
+		p.buffer.Truncate(p.buffer.Len() - len(e.sep))
+		return e.truncatePartialResultIfNeed(sctx, p.buffer)
+	}
+	return nil
 }
 
 type partialResult4GroupConcatDistinct struct {
@@ -133,6 +136,7 @@ func (e *groupConcatDistinct) UpdatePartialResult(sctx sessionctx.Context, rowsI
 	p := (*partialResult4GroupConcatDistinct)(pr)
 	v, isNull := "", false
 	for _, row := range rowsInGroup {
+		allIsNull := true
 		p.valsBuf.Reset()
 		for _, arg := range e.args {
 			v, isNull, err = arg.EvalString(sctx, row)
@@ -142,8 +146,12 @@ func (e *groupConcatDistinct) UpdatePartialResult(sctx sessionctx.Context, rowsI
 			if isNull {
 				continue
 			}
+			allIsNull = false
 			p.valsBuf.WriteString(v)
 		}
+		if allIsNull {
+			continue
+		}
 		joinedVals := p.valsBuf.String()
 		if p.valSet.exist(joinedVals) {
 			continue
@@ -158,5 +166,8 @@ func (e *groupConcatDistinct) UpdatePartialResult(sctx sessionctx.Context, rowsI
 		// write values
 		p.buffer.WriteString(joinedVals)
 	}
-	return e.truncatePartialResultIfNeed(sctx, p.buffer)
+	if p.buffer != nil {
+		return e.truncatePartialResultIfNeed(sctx, p.buffer)
+	}
+	return nil
 }
diff --git a/executor/aggregate_test.go b/executor/aggregate_test.go
@@ -320,6 +320,11 @@ func (s *testSuite) TestAggregation(c *C) {
 	result.Check(testkit.Rows(string([]byte{0x0}), string([]byte{0x1})))
 	result = tk.MustQuery("select cast(a as signed) as idx, cast(max(a) as signed),  cast(min(a) as signed) from t group by 1 order by idx")
 	result.Check(testkit.Rows("0 0 0", "1 1 1"))
+
+	tk.MustExec("drop table t")
+	tk.MustExec("create table t(a int)")
+	tk.MustExec("insert into t value(null)")
+	tk.MustQuery("select group_concat(a), group_concat(distinct a) from t").Check(testkit.Rows("<nil> <nil>"))
 }
 
 func (s *testSuite) TestStreamAggPushDown(c *C) {