From 0b642f63efea94334f81297f3e4214b863fe3391 Mon Sep 17 00:00:00 2001
From: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
Date: Thu, 2 Sep 2021 18:28:14 +0800
Subject: [PATCH] expression: fix unexpected constant fold when year compare
 string (#23281) (#23336)

---
 expression/builtin_compare.go  |  8 ++++----
 expression/integration_test.go | 10 ++++++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/expression/builtin_compare.go b/expression/builtin_compare.go
index 5225ddf773337..5d8afe1696916 100644
--- a/expression/builtin_compare.go
+++ b/expression/builtin_compare.go
@@ -1324,15 +1324,15 @@ func RefineComparedConstant(ctx sessionctx.Context, targetFieldType types.FieldT
 			// We try to convert the string constant to double.
 			// If the double result equals the int result, we can return the int result;
 			// otherwise, the compare function will be false.
+			// **Notice**
+			// we can not compare double result to int result directly, because year type will change its value, like
+			// 2 to 2002, here we just check whether double value equal int(double value). We can assert the int(string)
 			var doubleDatum types.Datum
 			doubleDatum, err = dt.ConvertTo(sc, types.NewFieldType(mysql.TypeDouble))
 			if err != nil {
 				return con, false
 			}
-			if c, err = doubleDatum.CompareDatum(sc, &intDatum); err != nil {
-				return con, false
-			}
-			if c != 0 {
+			if doubleDatum.GetFloat64() != math.Trunc(doubleDatum.GetFloat64()) {
 				return con, true
 			}
 			return &Constant{
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 5881820b40d54..62671a1fba58d 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -8949,6 +8949,16 @@ func (s *testIntegrationSuite) Test22717(c *C) {
 	tk.MustQuery("select d from t where d").Check(testkit.Rows("0", "1", "0,1"))
 }
 
+func (s *testIntegrationSuite) Test23262(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 year)")
+	tk.MustExec("insert into t values(2002)")
+	tk.MustQuery("select * from t where a=2").Check(testkit.Rows("2002"))
+	tk.MustQuery("select * from t where a='2'").Check(testkit.Rows("2002"))
+}
+
 func (s *testIntegrationSerialSuite) TestPartitionPruningRelaxOP(c *C) {
 	// Discovered while looking at issue 19941 (not completely related)
 	// relaxOP relax the op > to >= and < to <=