expression: fix a bug that DML using caseWhen may cause schema change (…

…#19857)

Signed-off-by: wjhuang2016 <huangwenjun1997@gmail.com>

expression/aggregation/base_func.go

@@ -414,17 +414,14 @@ func (a *baseFuncDesc) WrapCastForAggArgs(ctx sessionctx.Context) {
 		// function.
 		// Note: If the `Tp` of argument is the same as the `Tp` of the
 		// aggregation function, it will not wrap cast function on it
-		// internally. The reason of the special handling for `Column` is
-		// that the `RetType` of `Column` refers to the `infoschema`, so we
-		// need to set a new variable for it to avoid modifying the
-		// definition in `infoschema`.
-		if col, ok := a.Args[i].(*expression.Column); ok {
-			col.RetType = types.NewFieldType(col.RetType.Tp)
+		// internally.
+		switch x := a.Args[i].(type) {
+		case *expression.Column:
+			x.RetType = a.RetTp
+		case *expression.ScalarFunction:
+			x.RetType = a.RetTp
+		case *expression.CorrelatedColumn:
+			x.RetType = a.RetTp
 		}
-		// originTp is used when the the `Tp` of column is TypeFloat32 while
-		// the type of the aggregation function is TypeFloat64.
-		originTp := a.Args[i].GetType().Tp
-		*(a.Args[i].GetType()) = *(a.RetTp)
-		a.Args[i].GetType().Tp = originTp
 	}
 }

expression/constant_fold.go

@@ -122,7 +122,7 @@ func caseWhenHandler(expr *ScalarFunction) (Expression, bool) {
 					foldedExpr.GetType().Decimal = expr.GetType().Decimal
 					return foldedExpr, isDeferredConst
 				}
-				return BuildCastFunction(expr.GetCtx(), foldedExpr, foldedExpr.GetType()), isDeferredConst
+				return foldedExpr, isDeferredConst
 			}
 		} else {
 			// for no-const, here should return directly, because the following branches are unknown to be run or not

expression/integration_test.go

@@ -139,6 +139,19 @@ func (s *testIntegrationSuite) Test19654(c *C) {
 	tk.MustQuery("select /*+ inl_join(t2)*/ * from t1, t2 where t1.b=t2.b;").Check(testkit.Rows("a a"))
 }
 
+func (s *testIntegrationSuite) Test19387(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("USE test;")
+
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("create table t(a decimal(16, 2));")
+	tk.MustExec("select sum(case when 1 then a end) from t group by a;")
+	res := tk.MustQuery("show create table t")
+	c.Assert(len(res.Rows()), Equals, 1)
+	str := res.Rows()[0][1].(string)
+	c.Assert(strings.Contains(str, "decimal(16,2)"), IsTrue)
+}
+
 func (s *testIntegrationSuite) TestFuncREPEAT(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	defer s.cleanEnv(c)
@@ -3673,6 +3686,7 @@ func (s *testIntegrationSuite) TestAggregationBuiltin(c *C) {
 	defer s.cleanEnv(c)
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a decimal(7, 6))")
 	tk.MustExec("insert into t values(1.123456), (1.123456)")
 	result := tk.MustQuery("select avg(a) from t")