From fc89a6421a4c3ace8624ba17ac127e958d422732 Mon Sep 17 00:00:00 2001
From: lysu <sulifx@gmail.com>
Date: Tue, 14 Aug 2018 13:20:01 +0800
Subject: [PATCH] expression,ddl: fix fraction part handle of current_timestamp
 (#7355)

---
 ddl/db_test.go            |  2 +-
 executor/executor_test.go | 34 ++++++++++++++++++++++++++++++++++
 expression/helper.go      |  3 ++-
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/ddl/db_test.go b/ddl/db_test.go
index 69921cb423071..e134ddadbc615 100644
--- a/ddl/db_test.go
+++ b/ddl/db_test.go
@@ -1760,7 +1760,7 @@ func (s *testDBSuite) TestTableDDLWithTimeType(c *C) {
 	s.testErrorCode(c, "alter table t change column a aa time(7)", tmysql.ErrTooBigPrecision)
 	s.testErrorCode(c, "alter table t change column a aa datetime(7)", tmysql.ErrTooBigPrecision)
 	s.testErrorCode(c, "alter table t change column a aa timestamp(7)", tmysql.ErrTooBigPrecision)
-	s.mustExec(c, "alter table t change column a aa timestamp(0)")
+	s.mustExec(c, "alter table t change column a aa datetime(0)")
 	s.mustExec(c, "drop table t")
 }
 
diff --git a/executor/executor_test.go b/executor/executor_test.go
index e2e53470e550e..ae0156ea61570 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -3088,3 +3088,37 @@ func (s *testSuite) TestMaxOneRow(c *C) {
 	err = rs.Close()
 	c.Assert(err, IsNil)
 }
+
+func (s *testSuite) TestCurrentTimestampValueSelection(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t,t1")
+
+	tk.MustExec("create table t (id int, t0 timestamp null default current_timestamp, t1 timestamp(1) null default current_timestamp(1), t2 timestamp(2) null default current_timestamp(2) on update current_timestamp(2))")
+	tk.MustExec("insert into t (id) values (1)")
+	rs := tk.MustQuery("select t0, t1, t2 from t where id = 1")
+	t0 := rs.Rows()[0][0].(string)
+	t1 := rs.Rows()[0][1].(string)
+	t2 := rs.Rows()[0][2].(string)
+	c.Assert(len(strings.Split(t0, ".")), Equals, 1)
+	c.Assert(len(strings.Split(t1, ".")[1]), Equals, 1)
+	c.Assert(len(strings.Split(t2, ".")[1]), Equals, 2)
+	tk.MustQuery("select id from t where t0 = ?", t0).Check(testkit.Rows("1"))
+	tk.MustQuery("select id from t where t1 = ?", t1).Check(testkit.Rows("1"))
+	tk.MustQuery("select id from t where t2 = ?", t2).Check(testkit.Rows("1"))
+	time.Sleep(time.Second / 2)
+	tk.MustExec("update t set t0 = now() where id = 1")
+	rs = tk.MustQuery("select t2 from t where id = 1")
+	newT2 := rs.Rows()[0][0].(string)
+	c.Assert(newT2 != t2, IsTrue)
+
+	tk.MustExec("create table t1 (id int, a timestamp, b timestamp(2), c timestamp(3))")
+	tk.MustExec("insert into t1 (id, a, b, c) values (1, current_timestamp(2), current_timestamp, current_timestamp(3))")
+	rs = tk.MustQuery("select a, b, c from t1 where id = 1")
+	a := rs.Rows()[0][0].(string)
+	b := rs.Rows()[0][1].(string)
+	d := rs.Rows()[0][2].(string)
+	c.Assert(len(strings.Split(a, ".")), Equals, 1)
+	c.Assert(strings.Split(b, ".")[1], Equals, "00")
+	c.Assert(len(strings.Split(d, ".")[1]), Equals, 3)
+}
diff --git a/expression/helper.go b/expression/helper.go
index a7bc83fcb7770..813f45e903c85 100644
--- a/expression/helper.go
+++ b/expression/helper.go
@@ -14,6 +14,7 @@
 package expression
 
 import (
+	"math"
 	"strings"
 	"time"
 
@@ -57,7 +58,7 @@ func GetTimeValue(ctx sessionctx.Context, v interface{}, tp byte, fsp int) (d ty
 	case string:
 		upperX := strings.ToUpper(x)
 		if upperX == strings.ToUpper(ast.CurrentTimestamp) {
-			value.Time = types.FromGoTime(defaultTime)
+			value.Time = types.FromGoTime(defaultTime.Truncate(time.Duration(math.Pow10(9-fsp)) * time.Nanosecond))
 			if tp == mysql.TypeTimestamp {
 				err = value.ConvertTimeZone(time.Local, ctx.GetSessionVars().Location())
 				if err != nil {