json: don't resize slice to get extra zero when the length is unspeci…

…fied (#51586) (#52194)

close #51547

expression/builtin_cast.go

@@ -722,7 +722,7 @@ func (b *builtinCastStringAsJSONSig) evalJSON(row chunk.Row) (res types.BinaryJS
 	typ := b.args[0].GetType()
 	if types.IsBinaryStr(typ) {
 		buf := []byte(val)
-		if typ.GetType() == mysql.TypeString {
+		if typ.GetType() == mysql.TypeString && typ.GetFlen() > 0 {
 			// the tailing zero should also be in the opaque json
 			buf = make([]byte, typ.GetFlen())
 			copy(buf, val)

expression/builtin_cast_vec.go

@@ -843,7 +843,7 @@ func (b *builtinCastStringAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *chu
 
 			val := buf.GetBytes(i)
 			resultBuf := val
-			if typ.GetType() == mysql.TypeString {
+			if typ.GetType() == mysql.TypeString && typ.GetFlen() > 0 {
 				// only for BINARY: the tailing zero should also be in the opaque json
 				resultBuf = make([]byte, typ.GetFlen())
 				copy(resultBuf, val)

expression/integration_test.go

@@ -8046,3 +8046,21 @@ func TestIssue51765(t *testing.T) {
 	tk.MustQuery("select collation(ifnull(concat(NULL),id)) from t1;").Check(testkit.Rows("utf8mb4_general_ci"))
 	tk.MustQuery("select collation(ifnull(concat(NULL),ifnull(concat(NULL),id))) from t1;").Check(testkit.Rows("utf8mb4_general_ci"))
 }
+
+func TestCastBinaryStringToJSON(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustQuery("select cast(binary 'aa' as json);").Check(testkit.Rows(`"base64:type254:YWE="`))
+	tk.MustExec("create table t (vb VARBINARY(10), b BINARY(10), vc VARCHAR(10), c CHAR(10));")
+	tk.MustExec("insert into t values ('1', '1', '1', '1');")
+
+	tk.MustQuery("select cast(vb as json), cast(b as json), cast(vc as json), cast(c as json) from t;").Check(testkit.Rows(`"base64:type15:MQ==" "base64:type254:MQAAAAAAAAAAAA==" 1 1`))
+	tk.MustQuery("select 1 from t where cast(vb as json) = '1';").Check(testkit.Rows())
+	tk.MustQuery("select 1 from t where cast(b as json) = '1';").Check(testkit.Rows())
+	tk.MustQuery("select 1 from t where cast(vc as json) = '1';").Check(testkit.Rows())
+	tk.MustQuery("select 1 from t where cast(c as json) = '1';").Check(testkit.Rows())
+	tk.MustQuery("select 1 from t where cast(BINARY vc as json) = '1';").Check(testkit.Rows())
+	tk.MustQuery("select 1 from t where cast(BINARY c as json) = '1';").Check(testkit.Rows())
+}