expression: fix the panic when we use unix_time expression in `prep…

…are and execute` statement. (#17855)

* expression: fix Const.DeferredExpr's wrong behavior

* clean the code

* FIX UT

* revert the change and add check for `funcCallToExpression`

* solve conflicts

* fix typo

* address comments

Co-authored-by: pingcap-github-bot <sre-bot@pingcap.com>

expression/integration_test.go

@@ -6620,6 +6620,42 @@ func (s *testIntegrationSuite) TestIssue17287(c *C) {
 	tk.MustQuery("execute stmt7 using @val2;").Check(testkit.Rows("1589873946"))
 }
 
+func (s *testIntegrationSuite) TestIssue17727(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	orgEnable := plannercore.PreparedPlanCacheEnabled()
+	defer func() {
+		plannercore.SetPreparedPlanCache(orgEnable)
+	}()
+	plannercore.SetPreparedPlanCache(true)
+	var err error
+	tk.Se, err = session.CreateSession4TestWithOpt(s.store, &session.Opt{
+		PreparedPlanCache: kvcache.NewSimpleLRUCache(100, 0.1, math.MaxUint64),
+	})
+	c.Assert(err, IsNil)
+
+	tk.MustExec("use test;")
+	tk.MustExec("DROP TABLE IF EXISTS t1;")
+	tk.MustExec("CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, a timestamp NOT NULL);")
+	tk.MustExec("INSERT INTO t1 VALUES (null, '2020-05-30 20:30:00');")
+	tk.MustExec("PREPARE mystmt FROM 'SELECT * FROM t1 WHERE UNIX_TIMESTAMP(a) >= ?';")
+	tk.MustExec("SET @a=1590868800;")
+	tk.MustQuery("EXECUTE mystmt USING @a;").Check(testkit.Rows())
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("0"))
+
+	tk.MustExec("SET @a=1590868801;")
+	tk.MustQuery("EXECUTE mystmt USING @a;").Check(testkit.Rows())
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("1"))
+
+	tk.MustExec("prepare stmt from 'select unix_timestamp(?)';")
+	tk.MustExec("set @a = '2020-05-30 20:30:00';")
+	tk.MustQuery("execute stmt using @a;").Check(testkit.Rows("1590841800"))
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("0"))
+
+	tk.MustExec("set @a = '2020-06-12 13:47:58';")
+	tk.MustQuery("execute stmt using @a;").Check(testkit.Rows("1591940878"))
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("1"))
+}
+
 func (s *testIntegrationSerialSuite) TestIssue17891(c *C) {
 	collate.SetNewCollationEnabledForTest(true)
 	defer collate.SetNewCollationEnabledForTest(false)

planner/core/expression_rewriter.go

@@ -1526,9 +1526,16 @@ func (er *expressionRewriter) funcCallToExpression(v *ast.FuncCallExpr) {
 	var function expression.Expression
 	er.ctxStackPop(len(v.Args))
 	if _, ok := expression.DeferredFunctions[v.FnName.L]; er.useCache() && ok {
-		function, er.err = expression.NewFunctionBase(er.sctx, v.FnName.L, &v.Type, args...)
-		c := &expression.Constant{Value: types.NewDatum(nil), RetType: function.GetType().Clone(), DeferredExpr: function}
-		er.ctxStackAppend(c, types.EmptyName)
+		// When the expression is unix_timestamp and the number of argument is not zero,
+		// we deal with it as normal expression.
+		if v.FnName.L == ast.UnixTimestamp && len(v.Args) != 0 {
+			function, er.err = er.newFunction(v.FnName.L, &v.Type, args...)
+			er.ctxStackAppend(function, types.EmptyName)
+		} else {
+			function, er.err = expression.NewFunctionBase(er.sctx, v.FnName.L, &v.Type, args...)
+			c := &expression.Constant{Value: types.NewDatum(nil), RetType: function.GetType().Clone(), DeferredExpr: function}
+			er.ctxStackAppend(c, types.EmptyName)
+		}
 	} else {
 		function, er.err = er.newFunction(v.FnName.L, &v.Type, args...)
 		er.ctxStackAppend(function, types.EmptyName)