'Explain' button in Query Workbench produces broken/empty modal on malformed query

[stockholmux]

Input an invalid query - example:

SHOW tables LIKE 1;

Then click the 'Explain' button you get a strange, empty UI modal:

I would expect an error message, not an empty box. I assume this is related #586 .

[chloe-zh]

Hi @stockholmux thank you for reporting this issue, will do the enhancement once we have resources.

[davidcui1225]

Related: #404
Need to determine what the best behavior for Explain on SHOW/DESCRIBE queries are

[dai-chen]

I checked other database like MySQL. It doesn't allow EXPLAIN on metadata queries such as SHOW/DESCRIBE. In our case, I think EXPLAIN should only work with queries and disabled for other statements from both frontend and backend.

mysql> DESCRIBE accounts;
+-------+------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------+------+-----+---------+-------+
| age   | int  | YES  |     | NULL    |       |
+-------+------+------+-----+---------+-------+
1 row in set (0.00 sec)

mysql> EXPLAIN DESCRIBE accounts;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DESCRIBE accounts' at line 1

MySQL doc: https://dev.mysql.com/doc/refman/8.0/en/explain.html

explainable_stmt: {
    SELECT statement
  | TABLE statement
  | DELETE statement
  | INSERT statement
  | REPLACE statement
  | UPDATE statement
}

[davidcui1225]

Looks like Solution Plan will have to come in 2 places:

• Query Workbench: Disable Explain button on front-end for all non-SELECT queries
• SQL/PPL: Throw Exception in backend with clear error message that Explain is not supported for non-SELECT queries

[davidcui1225]

Fixed in #872