From f365238981a577e25e86029060947e67d729e08a Mon Sep 17 00:00:00 2001
From: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
Date: Mon, 8 Nov 2021 10:37:03 +0800
Subject: [PATCH] expression: fix wrong caseWhen function for enum type
 (#29454) (#29512)

---
 expression/builtin_control.go  |  8 ++++++++
 expression/constant_fold.go    |  2 +-
 expression/integration_test.go | 13 +++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/expression/builtin_control.go b/expression/builtin_control.go
index e9b39bf36ab5c..6ea2c119176c7 100644
--- a/expression/builtin_control.go
+++ b/expression/builtin_control.go
@@ -237,6 +237,14 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		return nil, err
 	}
 	bf.tp = fieldTp
+	if fieldTp.Tp == mysql.TypeEnum || fieldTp.Tp == mysql.TypeSet {
+		switch tp {
+		case types.ETInt:
+			fieldTp.Tp = mysql.TypeLonglong
+		case types.ETString:
+			fieldTp.Tp = mysql.TypeVarchar
+		}
+	}
 
 	switch tp {
 	case types.ETInt:
diff --git a/expression/constant_fold.go b/expression/constant_fold.go
index f08a5c45abf60..d7cbaf5d8edd6 100644
--- a/expression/constant_fold.go
+++ b/expression/constant_fold.go
@@ -143,7 +143,7 @@ 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
 	}
 	return expr, isDeferredConst
 }
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 6e3cae50fe249..22338090000c4 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -9936,6 +9936,19 @@ func (s *testIntegrationSuite) TestControlFunctionWithEnumOrSet(c *C) {
 	tk.MustExec("insert into t values(1,1,1),(2,1,1),(1,1,1),(2,1,1);")
 	tk.MustQuery("select if(A, null,b)=1 from t;").Check(testkit.Rows("<nil>", "<nil>", "<nil>", "<nil>"))
 	tk.MustQuery("select if(A, null,b)='a' from t;").Check(testkit.Rows("<nil>", "<nil>", "<nil>", "<nil>"))
+
+	// issue 29357
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("create table t(`a` enum('y','b','Abc','null','1','2','0')) CHARSET=binary;")
+	tk.MustExec("insert into t values(\"1\");")
+	tk.MustQuery("SELECT count(*) from t where (null like 'a') = (case when cast('2015' as real) <=> round(\"1200\",\"1\") then a end);\n").Check(testkit.Rows("0"))
+	tk.MustQuery("SELECT (null like 'a') = (case when cast('2015' as real) <=> round(\"1200\",\"1\") then a end) from t;\n").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 0 then a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 0 then a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 1 then a end) from t;").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 1 then a end) from t;").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 1 then a else a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 1 then a else a end) from t;").Check(testkit.Rows("1"))
 }
 
 func (s *testIntegrationSuite) TestComplexShowVariables(c *C) {