From 63fb86b4c83b6f227737e7bb813c20d2d37902a4 Mon Sep 17 00:00:00 2001
From: Ti Chi Robot <ti-community-prow-bot@tidb.io>
Date: Mon, 26 Jun 2023 15:16:05 +0800
Subject: [PATCH] executor: fix issue of update with same foreign key value
 returns error (#44907) (#44928)

close pingcap/tidb#44848
---
 executor/fktest/BUILD.bazel         |  2 +-
 executor/fktest/foreign_key_test.go | 12 ++++++++++++
 executor/foreign_key.go             | 24 ++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/executor/fktest/BUILD.bazel b/executor/fktest/BUILD.bazel
index ebaf679ce1ae8..cbf2536c7a4d3 100644
--- a/executor/fktest/BUILD.bazel
+++ b/executor/fktest/BUILD.bazel
@@ -8,7 +8,7 @@ go_test(
         "main_test.go",
     ],
     flaky = True,
-    shard_count = 38,
+    shard_count = 39,
     deps = [
         "//config",
         "//executor",
diff --git a/executor/fktest/foreign_key_test.go b/executor/fktest/foreign_key_test.go
index 4b0a21e0308d0..def9344c1c833 100644
--- a/executor/fktest/foreign_key_test.go
+++ b/executor/fktest/foreign_key_test.go
@@ -2865,3 +2865,15 @@ func TestForeignKeyAndSessionVariable(t *testing.T) {
 	tk.MustQuery("select * from t1").Check(testkit.Rows())
 	tk.MustQuery("select * from t2").Check(testkit.Rows())
 }
+
+func TestForeignKeyIssue44848(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("set @@foreign_key_checks=1")
+	tk.MustExec("use test")
+	tk.MustExec("create table b (  id int(11) NOT NULL AUTO_INCREMENT,  f int(11) NOT NULL,  PRIMARY KEY (id));")
+	tk.MustExec("create table a (  id int(11) NOT NULL AUTO_INCREMENT,  b_id int(11) NOT NULL,  PRIMARY KEY (id),  CONSTRAINT fk_b_id FOREIGN KEY (b_id) REFERENCES b (id) ON DELETE CASCADE);")
+	tk.MustExec("insert b(id,f) values(1,1);")
+	tk.MustExec("insert a(id,b_id) values(1,1);")
+	tk.MustExec("update b set id=1,f=2 where id=1;")
+}
diff --git a/executor/foreign_key.go b/executor/foreign_key.go
index 9908a72fd4b04..658808e714de2 100644
--- a/executor/foreign_key.go
+++ b/executor/foreign_key.go
@@ -34,6 +34,7 @@ import (
 	"github.com/pingcap/tidb/types"
 	driver "github.com/pingcap/tidb/types/parser_driver"
 	"github.com/pingcap/tidb/util/codec"
+	"github.com/pingcap/tidb/util/collate"
 	"github.com/pingcap/tidb/util/execdetails"
 	"github.com/pingcap/tidb/util/set"
 	"github.com/tikv/client-go/v2/txnkv/txnsnapshot"
@@ -161,6 +162,29 @@ func (fkc *FKCheckExec) insertRowNeedToCheck(sc *stmtctx.StatementContext, row [
 }
 
 func (fkc *FKCheckExec) updateRowNeedToCheck(sc *stmtctx.StatementContext, oldRow, newRow []types.Datum) error {
+	newVals, err := fkc.fetchFKValues(newRow)
+	if err != nil {
+		return err
+	}
+	oldVals, err := fkc.fetchFKValues(oldRow)
+	if err != nil {
+		return err
+	}
+	if len(oldVals) == len(newVals) {
+		isSameValue := true
+		for i := range oldVals {
+			cmp, err := oldVals[i].Compare(sc, &newVals[i], collate.GetCollator(oldVals[i].Collation()))
+			if err != nil || cmp != 0 {
+				isSameValue = false
+				break
+			}
+		}
+		if isSameValue {
+			// If the old fk value and the new fk value are the same, no need to check.
+			return nil
+		}
+	}
+
 	if fkc.FK != nil {
 		return fkc.addRowNeedToCheck(sc, newRow)
 	} else if fkc.ReferredFK != nil {