From ebaa8a720438f6bc92514a08c9403574a62ccde1 Mon Sep 17 00:00:00 2001
From: tsthght <781181214@qq.com>
Date: Tue, 8 Oct 2019 16:34:41 +0800
Subject: [PATCH] expression: implement vectorized evaluation for
 'builtinCastJSONAsStringSig' (#12542)

---
 expression/builtin_cast_vec.go      | 22 ++++++++++++++++++++--
 expression/builtin_cast_vec_test.go |  1 +
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index dce203af79..3999295db3 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -456,11 +456,29 @@ func (b *builtinCastJSONAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *chunk
 }
 
 func (b *builtinCastJSONAsStringSig) vectorized() bool {
-	return false
+	return true
 }
 
 func (b *builtinCastJSONAsStringSig) vecEvalString(input *chunk.Chunk, result *chunk.Column) error {
-	return errors.Errorf("not implemented")
+	n := input.NumRows()
+	buf, err := b.bufAllocator.get(types.ETJson, n)
+	if err != nil {
+		return err
+	}
+	defer b.bufAllocator.put(buf)
+	if err := b.args[0].VecEvalJSON(b.ctx, input, buf); err != nil {
+		return err
+	}
+
+	result.ReserveString(n)
+	for i := 0; i < n; i++ {
+		if buf.IsNull(i) {
+			result.AppendNull()
+			continue
+		}
+		result.AppendString(buf.GetJSON(i).String())
+	}
+	return nil
 }
 
 func (b *builtinCastDurationAsRealSig) vectorized() bool {
diff --git a/expression/builtin_cast_vec_test.go b/expression/builtin_cast_vec_test.go
index db21c6f55e..2ea368f913 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.ETJson}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETDecimal}},
 	},
 }