expression: implement vectorized evaluation for builtinLengthSig (p…

…ingcap#12636)

expression/builtin_string_vec.go

@@ -812,11 +812,33 @@ func (b *builtinInstrBinarySig) vecEvalInt(input *chunk.Chunk, result *chunk.Col
 }
 
 func (b *builtinLengthSig) vectorized() bool {
-	return false
+	return true
 }
 
+// vecEvalInt evaluates a builtinLengthSig.
+// See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html
 func (b *builtinLengthSig) vecEvalInt(input *chunk.Chunk, result *chunk.Column) error {
-	return errors.Errorf("not implemented")
+	n := input.NumRows()
+	buf, err := b.bufAllocator.get(types.ETString, n)
+	if err != nil {
+		return err
+	}
+	defer b.bufAllocator.put(buf)
+	if err := b.args[0].VecEvalString(b.ctx, input, buf); err != nil {
+		return err
+	}
+
+	result.ResizeInt64(n, false)
+	result.MergeNulls(buf)
+	i64s := result.Int64s()
+	for i := 0; i < n; i++ {
+		if result.IsNull(i) {
+			continue
+		}
+		str := buf.GetBytes(i)
+		i64s[i] = int64(len(str))
+	}
+	return nil
 }
 
 func (b *builtinLocate2ArgsSig) vectorized() bool {

expression/builtin_string_vec_test.go

@@ -22,7 +22,9 @@ import (
 )
 
 var vecBuiltinStringCases = map[string][]vecExprBenchCase{
-	ast.Length:         {},
+	ast.Length: {
+		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETString}, geners: []dataGenerator{&defaultGener{0.2, types.ETString}}},
+	},
 	ast.ASCII:          {},
 	ast.Concat:         {},
 	ast.ConcatWS:       {},