From b22ff44cb6b9d8e6e011714686edb302748927ca Mon Sep 17 00:00:00 2001
From: tsthght <781181214@qq.com>
Date: Wed, 9 Oct 2019 20:35:44 +0800
Subject: [PATCH] expression: implement vectorized evaluation for
 'builtinCastStringAsStringSig' (#12538)

---
 expression/builtin_cast_vec.go      | 37 +++++++++++++++++++++++++++--
 expression/builtin_cast_vec_test.go |  1 +
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index 5c9483fe37dab..889576e7653fb 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -792,11 +792,44 @@ func (b *builtinCastDecimalAsDurationSig) vecEvalDuration(input *chunk.Chunk, re
 }
 
 func (b *builtinCastStringAsStringSig) vectorized() bool {
-	return false
+	return true
 }
 
 func (b *builtinCastStringAsStringSig) vecEvalString(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
+	}
+
+	var res string
+	var isNull bool
+	sc := b.ctx.GetSessionVars().StmtCtx
+	result.ReserveString(n)
+	for i := 0; i < n; i++ {
+		if buf.IsNull(i) {
+			result.AppendNull()
+			continue
+		}
+		res, err = types.ProduceStrWithSpecifiedTp(buf.GetString(i), b.tp, sc, false)
+		if err != nil {
+			return err
+		}
+		res, isNull, err = padZeroForBinaryType(res, b.tp, b.ctx)
+		if err != nil {
+			return err
+		}
+		if isNull {
+			result.AppendNull()
+			continue
+		}
+		result.AppendString(res)
+	}
+	return nil
 }
 
 func (b *builtinCastJSONAsDurationSig) vectorized() bool {
diff --git a/expression/builtin_cast_vec_test.go b/expression/builtin_cast_vec_test.go
index 1c216583e4cc2..35df967686d4d 100644
--- a/expression/builtin_cast_vec_test.go
+++ b/expression/builtin_cast_vec_test.go
@@ -37,6 +37,7 @@ var vecBuiltinCastCases = map[string][]vecExprBenchCase{
 		},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETInt}},
 		{retEvalType: types.ETDecimal, childrenTypes: []types.EvalType{types.ETDatetime}},
+		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETString}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETDuration}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETDatetime}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETTimestamp}},