From 1a1736147b90b88119af3128c0149613c3b0e0e7 Mon Sep 17 00:00:00 2001
From: tsthght <781181214@qq.com>
Date: Thu, 17 Oct 2019 21:05:56 +0800
Subject: [PATCH 1/3] expression: implement vectorized evaluation for
 'builtinCastDecimalAsJSONSig'

---
 expression/builtin_cast_vec.go      | 30 +++++++++++++++++++++++++++--
 expression/builtin_cast_vec_test.go |  1 +
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index 2e8f7a87bbfb2..725e0ef4cddb1 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -1005,11 +1005,37 @@ func (b *builtinCastJSONAsDurationSig) vecEvalDuration(input *chunk.Chunk, resul
 }
 
 func (b *builtinCastDecimalAsJSONSig) vectorized() bool {
-	return false
+	return true
 }
 
 func (b *builtinCastDecimalAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *chunk.Column) error {
-	return errors.Errorf("not implemented")
+	n := input.NumRows()
+	buf, err := b.bufAllocator.get(types.ETDecimal, n)
+	if err != nil {
+		return err
+	}
+	defer b.bufAllocator.put(buf)
+	if err := b.args[0].VecEvalDecimal(b.ctx, input, buf); err != nil {
+		return err
+	}
+
+	result.ReserveJSON(n)
+	f64s := buf.Decimals()
+	var f float64
+	for i := 0; i < n; i++ {
+		if buf.IsNull(i) {
+			result.AppendJSON(json.BinaryJSON{})
+			result.SetNull(i, true)
+			continue
+		}
+		// FIXME: `select json_type(cast(1111.11 as json))` should return `DECIMAL`, we return `DOUBLE` now.
+		f, err = f64s[i].ToFloat64()
+		if err != nil {
+			return err
+		}
+		result.AppendJSON(json.CreateBinary(f))
+	}
+	return nil
 }
 
 func (b *builtinCastDurationAsJSONSig) vectorized() bool {
diff --git a/expression/builtin_cast_vec_test.go b/expression/builtin_cast_vec_test.go
index 484c4dccdc604..6496b1634c602 100644
--- a/expression/builtin_cast_vec_test.go
+++ b/expression/builtin_cast_vec_test.go
@@ -51,6 +51,7 @@ var vecBuiltinCastCases = map[string][]vecExprBenchCase{
 		{retEvalType: types.ETJson, childrenTypes: []types.EvalType{types.ETInt}},
 		{retEvalType: types.ETJson, childrenTypes: []types.EvalType{types.ETReal}},
 		{retEvalType: types.ETJson, childrenTypes: []types.EvalType{types.ETJson}},
+		{retEvalType: types.ETJson, childrenTypes: []types.EvalType{types.ETDecimal}},
 	},
 }
 

From 955af4d2d35200c7c031a10388d155e9fb76a366 Mon Sep 17 00:00:00 2001
From: tsthght <781181214@qq.com>
Date: Thu, 17 Oct 2019 21:06:29 +0800
Subject: [PATCH 2/3] refine

---
 expression/builtin_cast_vec.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index 725e0ef4cddb1..52da185c3fd98 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -1015,7 +1015,7 @@ func (b *builtinCastDecimalAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *ch
 		return err
 	}
 	defer b.bufAllocator.put(buf)
-	if err := b.args[0].VecEvalDecimal(b.ctx, input, buf); err != nil {
+	if err = b.args[0].VecEvalDecimal(b.ctx, input, buf); err != nil {
 		return err
 	}
 

From a02ca93be4b115086d5ad7bd89d19d0f0c648124 Mon Sep 17 00:00:00 2001
From: tsthght <781181214@qq.com>
Date: Thu, 17 Oct 2019 23:07:28 +0800
Subject: [PATCH 3/3] fix an error

---
 expression/builtin_cast_vec.go | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index 52da185c3fd98..4b8dbcfcfed21 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -1024,8 +1024,7 @@ func (b *builtinCastDecimalAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *ch
 	var f float64
 	for i := 0; i < n; i++ {
 		if buf.IsNull(i) {
-			result.AppendJSON(json.BinaryJSON{})
-			result.SetNull(i, true)
+			result.AppendNull()
 			continue
 		}
 		// FIXME: `select json_type(cast(1111.11 as json))` should return `DECIMAL`, we return `DOUBLE` now.