expression: Fix the issue that cast str as datetime with time_zone results in loss of precision

pkg/types/time.go

@@ -576,7 +576,10 @@ func GetFsp(s string) int {
 
 // GetFracIndex finds the last '.' for get fracStr, index = -1 means fracStr not found.
 // but for format like '2019.01.01 00:00:00', the index should be -1.
-// It will not be affected by the time zone suffix. For format like '2020-01-01 12:00:00.123456+05:00', the index should be 19.
+//
+// It will not be affected by the time zone suffix.
+// For format like '2020-01-01 12:00:00.123456+05:00' and `2020-01-01 12:00:00.123456-05:00`, the index should be 19.
+// related issue https://github.com/pingcap/tidb/issues/35291 and https://github.com/pingcap/tidb/issues/49555
 func GetFracIndex(s string) (index int) {
 	tzIndex, _, _, _, _ := GetTimezone(s)
 	var end int
@@ -587,7 +590,7 @@ func GetFracIndex(s string) (index int) {
 	}
 	index = -1
 	for i := end; i >= 0; i-- {
-		if unicode.IsPunct(rune(s[i])) {
+		if s[i] != '+' && s[i] != '-' && isPunctuation(s[i]) {
 			if s[i] == '.' {
 				index = i
 			}

pkg/types/time_test.go

@@ -114,6 +114,8 @@ func TestDateTime(t *testing.T) {
 
 		// For issue 35291
 		{"2020-01-01 12:00:00.123456+05:00", "2020-01-01 07:00:00.123456"},
+		// For issue 49555
+		{"2020-01-01 12:00:00.123456-05:00", "2020-01-01 17:00:00.123456"},
 	}
 
 	for _, test := range table {
@@ -1902,6 +1904,8 @@ func TestGetFracIndex(t *testing.T) {
 		{"2019.01.01 00:00:00", -1},
 		{"2019.01.01 00:00:00.1", 19},
 		{"12345.6", 5},
+		{"2020-01-01 12:00:00.123456 +0600 PST", 19},
+		{"2020-01-01 12:00:00.123456 -0600 PST", 19},
 	}
 	for _, testCase := range testCases {
 		index := types.GetFracIndex(testCase.str)

tests/integrationtest/r/expression/cast.result

@@ -78,6 +78,16 @@ select cast(col4 as time(31)) from t where col1 is null;
 Error 1426 (42000): Too big precision 31 specified for column 'CAST'. Maximum is 6.
 select cast(col5 as time(31)) from t where col1 is null;
 Error 1426 (42000): Too big precision 31 specified for column 'CAST'. Maximum is 6.
+drop table if exists t;
+create table t(a varchar(50));
+insert into t values ('2020-01-01 12:00:00.123456 +0600 PST');
+insert into t values ('2020-01-01 12:00:00.123456 -0600 PST');
+insert into t values ('2020-01-01 12:00:00.123456');
+select cast(a as datetime(3)) from t;
+cast(a as datetime(3))
+2020-01-01 12:00:00.123
+2020-01-01 12:00:00.123
+2020-01-01 12:00:00.123
 drop table if exists t1;
 create table t1 (c1 text);
 insert into t1 values ('a');

tests/integrationtest/t/expression/cast.test

@@ -45,6 +45,12 @@ select cast(col3 as time(31)) from t where col1 is null;
 select cast(col4 as time(31)) from t where col1 is null;
 -- error 1426
 select cast(col5 as time(31)) from t where col1 is null;
+drop table if exists t;
+create table t(a varchar(50));
+insert into t values ('2020-01-01 12:00:00.123456 +0600 PST');
+insert into t values ('2020-01-01 12:00:00.123456 -0600 PST');
+insert into t values ('2020-01-01 12:00:00.123456');
+select cast(a as datetime(3)) from t;
 
 # TestCastErrMsg
 drop table if exists t1;