executor: make seek value with the same length of the index columns.

For composite index with 2 columns, if we just pass one value in `Seek`, we will get the wrong result.
So this change create the seek value with the length of the composite index.

executor/builder.go

@@ -84,7 +84,7 @@ func (b *executorBuilder) buildIndexScan(v *plan.IndexScan) Executor {
 	}
 	e := &IndexScanExec{
 		tbl:        tbl,
-		idx:        idx.X,
+		idx:        idx,
 		fields:     v.Fields(),
 		ctx:        b.ctx,
 		Desc:       v.Desc,

executor/executor.go

@@ -19,6 +19,7 @@ import (
 
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/ast"
+	"github.com/pingcap/tidb/column"
 	"github.com/pingcap/tidb/context"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/optimizer/evaluator"
@@ -177,8 +178,8 @@ func (e *IndexRangeExec) Fields() []*ast.ResultField {
 // Next implements Executor Next interface.
 func (e *IndexRangeExec) Next() (*Row, error) {
 	if e.iter == nil {
-		seekVals := make([]interface{}, len(e.lowVals))
-		for i := 0; i < len(seekVals); i++ {
+		seekVals := make([]interface{}, len(e.scan.idx.Columns))
+		for i := 0; i < len(e.lowVals); i++ {
 			var err error
 			if e.lowVals[i] == plan.MinNotNullVal {
 				seekVals[i] = []byte{}
@@ -189,12 +190,11 @@ func (e *IndexRangeExec) Next() (*Row, error) {
 				}
 			}
 		}
-
 		txn, err := e.scan.ctx.GetTxn(false)
 		if err != nil {
 			return nil, errors.Trace(err)
 		}
-		e.iter, _, err = e.scan.idx.Seek(txn, seekVals)
+		e.iter, _, err = e.scan.idx.X.Seek(txn, seekVals)
 		if err != nil {
 			return nil, types.EOFAsNil(err)
 		}
@@ -315,7 +315,7 @@ func (e *IndexRangeExec) Close() error {
 // IndexScanExec represents an index scan executor.
 type IndexScanExec struct {
 	tbl        table.Table
-	idx        kv.Index
+	idx        *column.IndexedCol
 	fields     []*ast.ResultField
 	Ranges     []*IndexRangeExec
 	Desc       bool

kv/index_iter_test.go

@@ -143,3 +143,23 @@ func (s *testIndexSuite) TestIndex(c *C) {
 	err = txn.Commit()
 	c.Assert(err, IsNil)
 }
+
+func (s *testIndexSuite) TestCombineIndexSeek(c *C) {
+	index := kv.NewKVIndex("i", "test", 1, false)
+
+	txn, err := s.s.Begin()
+	c.Assert(err, IsNil)
+
+	values := []interface{}{"abc", "def"}
+	err = index.Create(txn, values, 1)
+	c.Assert(err, IsNil)
+
+	index2 := kv.NewKVIndex("i", "test", 1, false)
+	iter, hit, err := index2.Seek(txn, []interface{}{"abc", nil})
+	defer iter.Close()
+	c.Assert(err, IsNil)
+	c.Assert(hit, IsFalse)
+	_, h, err := iter.Next()
+	c.Assert(err, IsNil)
+	c.Assert(h, Equals, int64(1))
+}

session_test.go

@@ -1364,6 +1364,13 @@ func (s *testSessionSuite) TestMultiColumnIndex(c *C) {
 	checkPlan(c, se, sql, expectedExplain)
 	mustExecMatch(c, se, sql, [][]interface{}{{1}})
 
+	// Test varchar type.
+	mustExecSQL(c, se, "drop table t;")
+	mustExecSQL(c, se, "create table t (c1 varchar(64), c2 varchar(64), index c1_c2 (c1, c2));")
+	mustExecSQL(c, se, "insert into t values ('abc', 'def')")
+	sql = "select c1 from t where c1 = 'abc'"
+	mustExecMatch(c, se, sql, [][]interface{}{{[]byte("abc")}})
+
 	err := se.Close()
 	c.Assert(err, IsNil)
 }