server crash on GROUP BY indexed enum

[morgo]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (
 id INT NOT NULL PRIMARY KEY auto_increment,
 b varchar(255) NOT NULL,
 c ENUM('a', 'b', 'c', 'd', 'e'),
 INDEX (c)
);

INSERT INTO t1 VALUES 
 (NULL, REPEAT('b', 255), 'a'),
 (NULL, REPEAT('b', 255), 'b'),
 (NULL, REPEAT('b', 255), 'c'),
 (NULL, REPEAT('b', 255), 'd'),
 (NULL, REPEAT('b', 255), 'e');
 
SELECT c FROM t1 GROUP BY c;

2. What did you expect to see?

Not crash.

3. What did you see instead?

2018/08/07 14:43:43.857 conn.go:427: [error] lastCmd SELECT c FROM t1 GROUP BY c, runtime error: slice bounds out of range, goroutine 38207 [running]:
github.com/pingcap/tidb/server.(*clientConn).Run.func1(0xc42087b2b0, 0xc4209f5dff)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:425 +0x10e
panic(0x1155280, 0x1e09700)
        /usr/local/go/src/runtime/panic.go:502 +0x229
github.com/pingcap/tidb/server.(*clientConn).writeResultset.func1(0x0, 0x1445c00, 0xc420b0f2c0, 0xc4209f5bf8, 0xc42087b2b0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:943 +0x325
panic(0x1155280, 0x1e09700)
        /usr/local/go/src/runtime/panic.go:502 +0x229
github.com/pingcap/tidb/util/chunk.Row.getNameValue(0xc420aaeca0, 0x0, 0x0, 0x400, 0x573d1b, 0xc42096602a)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/util/chunk/row.go:106 +0x126
github.com/pingcap/tidb/util/chunk.Row.GetEnum(0xc420aaeca0, 0x0, 0x0, 0xc4209f5978, 0x1, 0x9)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/util/chunk/row.go:112 +0x3f
github.com/pingcap/tidb/server.dumpTextRow(0xc420625000, 0x4, 0x400, 0xc421869c80, 0x1, 0x1, 0xc420aaeca0, 0x0, 0x50, 0x121a620, ...)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/util.go:326 +0xcfe
github.com/pingcap/tidb/server.(*clientConn).writeChunks(0xc42087b2b0, 0x7f4649c81130, 0xc420f02d00, 0x1445c00, 0xc420b0f2c0, 0xc400005b00, 0xc42087b2b0, 0x0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:1015 +0x2c5
github.com/pingcap/tidb/server.(*clientConn).writeResultset(0xc42087b2b0, 0x7f4649c81130, 0xc420f02d00, 0x1445c00, 0xc420b0f2c0, 0xc400007c00, 0x0, 0x0, 0x0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:956 +0x1bc
github.com/pingcap/tidb/server.(*clientConn).handleQuery(0xc42087b2b0, 0x7f4649c81130, 0xc420f02d00, 0xc42003c681, 0x1b, 0x0, 0x0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:873 +0x124
github.com/pingcap/tidb/server.(*clientConn).dispatch(0xc42087b2b0, 0xc42003c681, 0x1c, 0x1c, 0x0, 0x0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:612 +0x4f9
github.com/pingcap/tidb/server.(*clientConn).Run(0xc42087b2b0)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/conn.go:470 +0x1be
github.com/pingcap/tidb/server.(*Server).onConn(0xc4207168a0, 0x14478e0, 0xc421869888)
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/server.go:324 +0x22b
created by github.com/pingcap/tidb/server.(*Server).Run
        /home/jenkins/workspace/build_tidb_master/go/src/github.com/pingcap/tidb/server/server.go:264 +0x4dc

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

MySQL [(none)]> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v2.1.0-beta-156-g5e7aa1d
Git Commit Hash: 5e7aa1d97d6459843949ae3587c9b5ac6661bb37
Git Branch: master
UTC Build Time: 2018-08-01 02:49:37
GoVersion: go version go1.10.2 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
1 row in set (0.00 sec)

[ciscoxll]

@XuHuaiyu PTAL.

[XuHuaiyu]

tidb> desc SELECT c FROM t1 GROUP BY c;
+----------------------+----------+------+---------------------------------------------------------------------+
| id                   | count    | task | operator info                                                       |
+----------------------+----------+------+---------------------------------------------------------------------+
| StreamAgg_8          | 8000.00  | root | group by:test.t1.c, funcs:firstrow(test.t1.c)                       |
| └─IndexReader_16     | 10000.00 | root | index:IndexScan_15                                                  |
|   └─IndexScan_15     | 10000.00 | cop  | table:t1, index:c, range:[NULL,+inf], keep order:true, stats:pseudo |
+----------------------+----------+------+---------------------------------------------------------------------+
3 rows in set (0.00 sec)

This may be caused by the wrong type inferring of firstrow(enum_col),
I'll solve this problem.