tables: fix prefix index, when the charset is utf8, truncate it from runes (#7109)

ddl/index.go

@@ -123,6 +123,7 @@ func buildIndexColumns(columns []*model.ColumnInfo, idxColNames []*ast.IndexColN
 			Name:   col.Name,
 			Offset: col.Offset,
 			Length: ic.Length,
+			Tp:     &col.FieldType,
 		})
 	}
 

expression/integration_test.go

@@ -3352,3 +3352,17 @@ func (s *testIntegrationSuite) TestTwoDecimalAssignTruncate(c *C) {
 	res := tk.MustQuery("select a, b from t1")
 	res.Check(testkit.Rows("123.12345 123.1"))
 }
+
+func (s *testIntegrationSuite) TestPrefixIndex(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	defer s.cleanEnv(c)
+	tk.MustExec("use test")
+	tk.MustExec(`CREATE TABLE t1 (
+  			name varchar(12) DEFAULT NULL,
+  			KEY pname (name(12))
+		) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci`)
+
+	tk.MustExec("insert into t1 values('借款策略集_网页');")
+	res := tk.MustQuery("select * from t1 where name = '借款策略集_网页';")
+	res.Check(testkit.Rows("借款策略集_网页"))
+}

model/model.go

@@ -285,6 +285,8 @@ type IndexColumn struct {
 	// for indexing;
 	// UnspecifedLength if not using prefix indexing
 	Length int `json:"length"`
+	// Tp is the index column field type.
+	Tp *types.FieldType
 }
 
 // Clone clones IndexColumn.

table/tables/index.go

@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"io"
+	"unicode/utf8"
 
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/kv"
@@ -26,6 +27,7 @@ import (
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/tablecodec"
 	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util/charset"
 	"github.com/pingcap/tidb/util/codec"
 )
 
@@ -125,6 +127,32 @@ func (c *index) getIndexKeyBuf(buf []byte, defaultCap int) []byte {
 	return make([]byte, 0, defaultCap)
 }
 
+// truncateIndexValuesIfNeeded truncate the index values that be created that use only the leading part of column values.
+func (c *index) truncateIndexValuesIfNeeded(indexedValues []types.Datum) []types.Datum {
+	for i := 0; i < len(indexedValues); i++ {
+		v := &indexedValues[i]
+		if v.Kind() == types.KindString || v.Kind() == types.KindBytes {
+			ic := c.idxInfo.Columns[i]
+			if ic.Tp.Charset == charset.CharsetUTF8 || ic.Tp.Charset == charset.CharsetUTF8MB4 {
+				val := v.GetBytes()
+				if ic.Length != types.UnspecifiedLength && utf8.RuneCount(val) > ic.Length {
+					rs := bytes.Runes(val)
+					truncateStr := string(rs[:ic.Length])
+					// truncate value and limit its length
+					v.SetString(truncateStr)
+				}
+			} else {
+				if ic.Length != types.UnspecifiedLength && len(v.GetBytes()) > ic.Length {
+					// truncate value and limit its length
+					v.SetBytes(v.GetBytes()[:ic.Length])
+				}
+			}
+		}
+	}
+
+	return indexedValues
+}
+
 // GenIndexKey generates storage key for index values. Returned distinct indicates whether the
 // indexed values should be distinct in storage (i.e. whether handle is encoded in the key).
 func (c *index) GenIndexKey(sc *stmtctx.StatementContext, indexedValues []types.Datum, h int64, buf []byte) (key []byte, distinct bool, err error) {
@@ -144,16 +172,7 @@ func (c *index) GenIndexKey(sc *stmtctx.StatementContext, indexedValues []types.
 
 	// For string columns, indexes can be created that use only the leading part of column values,
 	// using col_name(length) syntax to specify an index prefix length.
-	for i := 0; i < len(indexedValues); i++ {
-		v := &indexedValues[i]
-		if v.Kind() == types.KindString || v.Kind() == types.KindBytes {
-			ic := c.idxInfo.Columns[i]
-			if ic.Length != types.UnspecifiedLength && len(v.GetBytes()) > ic.Length {
-				// truncate value and limit its length
-				v.SetBytes(v.GetBytes()[:ic.Length])
-			}
-		}
-	}
+	indexedValues = c.truncateIndexValuesIfNeeded(indexedValues)
 	key = c.getIndexKeyBuf(buf, len(c.prefix)+len(indexedValues)*9+9)
 	key = append(key, []byte(c.prefix)...)
 	key, err = codec.EncodeKey(sc, key, indexedValues...)

table/tables/index_test.go

@@ -210,8 +210,8 @@ func (s *testIndexSuite) TestCombineIndexSeek(c *C) {
 				ID:   2,
 				Name: model.NewCIStr("test"),
 				Columns: []*model.IndexColumn{
-					{},
-					{},
+					{Tp: &types.FieldType{}},
+					{Tp: &types.FieldType{}},
 				},
 			},
 		},