planner: cut prefix index according the character set (pingcap#30694)

close pingcap#30564
jackysp · Dec 30, 2021 · 24e7e5d · 24e7e5d
1 parent 8085c99
commit 24e7e5d
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Showing 2 changed files with 27 additions and 12 deletions.
diff --git a/executor/executor_test.go b/executor/executor_test.go
@@ -5842,6 +5842,19 @@ func (s *testSuiteWithCliBaseCharset) TestCharsetFeatureCollation(c *C) {
 	tk.MustGetErrCode("select collation(concat(ascii_char collate ascii_bin, gbk_char)) from t;", mysql.ErrCantAggregate2collations)
 }
 
+func (s *testSuiteWithCliBaseCharset) TestCharsetWithPrefixIndex(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 char(20) charset gbk, b char(20) charset gbk, primary key (a(2)));")
+	tk.MustExec("insert into t values ('a', '中文'), ('中文', '中文'), ('一二三', '一二三'), ('b', '一二三');")
+	tk.MustQuery("select * from t").Check(testkit.Rows("a 中文", "中文 中文", "一二三 一二三", "b 一二三"))
+	tk.MustExec("drop table t")
+	tk.MustExec("create table t(a char(20) charset gbk, b char(20) charset gbk, unique index idx_a(a(2)));")
+	tk.MustExec("insert into t values ('a', '中文'), ('中文', '中文'), ('一二三', '一二三'), ('b', '一二三');")
+	tk.MustQuery("select * from t").Check(testkit.Rows("a 中文", "中文 中文", "一二三 一二三", "b 一二三"))
+}
+
 func (s *testSerialSuite2) TestIssue23567(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	oriProbability := statistics.FeedbackProbability.Load()

diff --git a/tablecodec/tablecodec.go b/tablecodec/tablecodec.go
@@ -1300,21 +1300,23 @@ func TruncateIndexValue(v *types.Datum, idxCol *model.IndexColumn, tblCol *model
 	if notStringType {
 		return
 	}
-	originalKind := v.Kind()
-	isUTF8Charset := tblCol.Charset == charset.CharsetUTF8 || tblCol.Charset == charset.CharsetUTF8MB4
-	if isUTF8Charset && utf8.RuneCount(v.GetBytes()) > idxCol.Length {
-		rs := bytes.Runes(v.GetBytes())
+	colValue := v.GetBytes()
+	if tblCol.Charset == charset.CharsetBin || tblCol.Charset == charset.CharsetASCII {
+		// Count character length by bytes if charset is binary or ascii.
+		if len(colValue) > idxCol.Length {
+			// truncate value and limit its length
+			if v.Kind() == types.KindBytes {
+				v.SetBytes(colValue[:idxCol.Length])
+			} else {
+				v.SetString(v.GetString()[:idxCol.Length], tblCol.Collate)
+			}
+		}
+	} else if utf8.RuneCount(colValue) > idxCol.Length {
+		// Count character length by characters for other rune-based charsets, they are all internally encoded as UTF-8.
+		rs := bytes.Runes(colValue)
 		truncateStr := string(rs[:idxCol.Length])
 		// truncate value and limit its length
 		v.SetString(truncateStr, tblCol.Collate)
-		if v.Kind() == types.KindBytes {
-			v.SetBytes(v.GetBytes())
-		}
-	} else if !isUTF8Charset && len(v.GetBytes()) > idxCol.Length {
-		v.SetBytes(v.GetBytes()[:idxCol.Length])
-		if originalKind == types.KindString {
-			v.SetString(v.GetString(), tblCol.Collate)
-		}
 	}
 }