planner: fix name ambiguous check when building natural join without filter

pkg/planner/core/logical_plan_builder.go

@@ -1150,6 +1150,52 @@ func (b *PlanBuilder) coalesceCommonColumns(p *LogicalJoin, leftPlan, rightPlan
 		if err != nil {
 			return err
 		}
+	} else {
+		// Even with no using filter, we still should check the checkAmbiguous name before we try to find the common column from both side.
+		// (t3 cross join t4) natural join t1
+		//  t1 natural join (t3 cross join t4)
+		// t3 and t4 may generate the same name column from cross join.
+		// for every common column of natural join, the name from right or left should be exactly one.
+		commonNames := make([]string, 0, len(lNames))
+		lNameMap := make(map[string]int, len(lNames))
+		rNameMap := make(map[string]int, len(rNames))
+		for _, name := range lNames {
+			// Natural join should ignore _tidb_rowid
+			if name.ColName.L == "_tidb_rowid" {
+				continue
+			}
+			// record left map
+			if cnt, ok := lNameMap[name.ColName.L]; ok {
+				lNameMap[name.ColName.L] = cnt + 1
+			} else {
+				lNameMap[name.ColName.L] = 1
+			}
+		}
+		for _, name := range rNames {
+			// Natural join should ignore _tidb_rowid
+			if name.ColName.L == "_tidb_rowid" {
+				continue
+			}
+			// record right map
+			if cnt, ok := rNameMap[name.ColName.L]; ok {
+				rNameMap[name.ColName.L] = cnt + 1
+			} else {
+				rNameMap[name.ColName.L] = 1
+			}
+			// check left map
+			if cnt, ok := lNameMap[name.ColName.L]; ok {
+				if cnt > 1 {
+					return plannererrors.ErrAmbiguous.GenWithStackByArgs(name.ColName.L, "from clause")
+				}
+				commonNames = append(commonNames, name.ColName.L)
+			}
+		}
+		// check right map
+		for _, commonName := range commonNames {
+			if rNameMap[commonName] > 1 {
+				return plannererrors.ErrAmbiguous.GenWithStackByArgs(commonName, "from clause")
+			}
+		}
 	}
 
 	// Find out all the common columns and put them ahead.

tests/integrationtest/r/executor/jointest/join.result

@@ -1590,3 +1590,16 @@ insert into t1 values(2,3),(4,4);
 select /*+ TIDB_HJ(t, t2) */ * from t, t1 where t.c1 = t1.c1;
 c1	c2	c1	c2
 2	2	2	3
+drop table if exists t1,t2,t3,t4;
+create table t1 (c int, b int);
+create table t2 (a int, b int);
+create table t3 (b int, c int);
+create table t4 (y int, c int);
+select * from t1 natural join (t3 cross join t4);
+Error 1052 (23000): Column 'c' in from clause is ambiguous
+select * from (t3 cross join t4) natural join t1;
+Error 1052 (23000): Column 'c' in from clause is ambiguous
+select * from (t1 join t2 on t1.b=t2.b) natural join (t3 natural join t4);
+Error 1052 (23000): Column 'b' in from clause is ambiguous
+select * from (t3 natural join t4) natural join (t1 join t2 on t1.b=t2.b);
+Error 1052 (23000): Column 'b' in from clause is ambiguous

tests/integrationtest/t/executor/jointest/join.test

@@ -1089,3 +1089,18 @@ create table t1(c1 int, c2 int);
 insert into t values(1,1),(2,2);
 insert into t1 values(2,3),(4,4);
 select /*+ TIDB_HJ(t, t2) */ * from t, t1 where t.c1 = t1.c1;
+
+# TestIssue30244
+drop table if exists t1,t2,t3,t4;
+create table t1 (c int, b int);
+create table t2 (a int, b int);
+create table t3 (b int, c int);
+create table t4 (y int, c int);
+--error 1052
+select * from t1 natural join (t3 cross join t4);
+--error 1052
+select * from (t3 cross join t4) natural join t1;
+--error 1052
+select * from (t1 join t2 on t1.b=t2.b) natural join (t3 natural join t4);
+--error 1052
+select * from (t3 natural join t4) natural join (t1 join t2 on t1.b=t2.b);