GROUP_CONCAT error. subquery returns more than 1 row

[799983050]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

SELECT ( SELECT GROUP_CONCAT( CONCAT( 123, '-' ) ) FROM user_info ui WHERE ui.id = read_cust_user_id GROUP BY ui.id ) AS levelCode FROM ods_order_item_base_two
Error information is ：

1105 - subquery returns more than 1 row
Remarks：
read_cust_user_id is ods_order_item_base_two table field。

2. What did you expect to see?

Give an explanation.

3. What did you see instead?
   GROUP BY ui.id
   Change to
   GROUP BY read_cust_user_id
   Successful implementation
4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   Release Version: v2.1.1
   Git Commit Hash: 990f859
   Git Branch: release-2.1
   UTC Build Time: 2018-12-12 10:57:44
   GoVersion: go version go1.11.2 linux/amd64
   Race Enabled: false
   TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
   Check Table Before Drop: false

[XuHuaiyu]

Hi, @799983050 Thanks for your feedback.
The case you mentioned is weird.
I tried to build a simple case to reproduce it but failed.
May you provide us the table schema and data which can reproduce this problem?

tidb> select * from t;
+------+
| a    |
+------+
|    1 |
|    1 |
|    2 |
|    2 |
+------+
4 rows in set (0.00 sec)

tidb> select * from s;
+------+
| a    |
+------+
|    2 |
|    2 |
|    1 |
|    1 |
+------+
4 rows in set (0.00 sec)

tidb>  SELECT ( SELECT GROUP_CONCAT( CONCAT( 123, '-' ) ) FROM t WHERE t.a = s.a GROUP BY t.a ) AS t FROM s;
+-----------+
| t         |
+-----------+
| 123-,123- |
| 123-,123- |
| 123-,123- |
| 123-,123- |
+-----------+
4 rows in set (0.00 sec)

[799983050]

@XuHuaiyu Hello, I created a model for you to find problems.
`
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

DROP TABLE IF EXISTS t;
CREATE TABLE t (
id int(11) NOT NULL,
PRIMARY KEY (id) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 100 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;

INSERT INTO t VALUES (508931);
INSERT INTO t VALUES (508932);

SET FOREIGN_KEY_CHECKS = 1;

`

`
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

DROP TABLE IF EXISTS s;
CREATE TABLE s (
id int(11) NOT NULL,
read_cust_user_id int(11) NOT NULL,
PRIMARY KEY (id) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 100 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;

INSERT INTO s VALUES (100292, 508931);
INSERT INTO s VALUES (120002, 508932);

SET FOREIGN_KEY_CHECKS = 1;`