Digester produces invalid sql for selecting global variables

[wwar]

Bug Report

1. Minimal reproduce step (Required)

The digester produces an invalid SQL for the following statement:

SELECT @@global.tidb_stmt_summary_refresh_interval AS value

This statement is generated by the tidb-dashboard.

I have another digester bug in #14241 - it is annoying when the syntax generated back is invalid.

2. What did you expect to see? (Required)

SELECT @@global.tidb_stmt_summary_refresh_interval AS value

3. What did you see instead (Required)

There is a space between the two @ symbols:

SELECT @ @global.tidb_stmt_summary_refresh_interval AS value

4. Affected version (Required)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-684-gf590d74e1
Edition: Community
Git Commit Hash: f590d74e158cf4e33555bfeb8f88971af5956697
Git Branch: master
UTC Build Time: 2020-06-27 02:29:48
GoVersion: go1.13.8
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

5. Root Cause Analysis

[HunDunDM]

/label component/parser

[wjhuang2016]

@nullnotnil I can't reproduce it in both v4.0.8 and master, could you reproduce it?

[crazycs520]

@wjhuang2016 I can reproduce it, It may be caused by dashboard format SQL before display.

[wjhuang2016]

I move it to the dashboard's repo and close it now.