How to check if MySQL query is valid without executing it?

Question

I'm making a simple tool that will get a string of MySQL commands and run it (on several DB servers sequentially). I trust the users to be sensible, but mistakes happen, and I'm looking for a way to prevent basic typos:

Is there a way to validate, at runtime, (relatively simple) MySQL queries to see if they're syntactically correct?

I'm not looking for semantic correctness, eg table names or join applicability; just something like a spellcheck for SQL queries.

In other words,

SELECT * FROM x;

or

INSERT INTO x SET id=1,bar="foo";

would be marked valid, whereas any of those would not:

SELECT FROM x;
SECLET * RFOM x;
ISNETR INTO x SET id=1;
HJBGYGCRYTCY;

For SELECT s, I could bend EXPLAIN to my needs - run EXPLAIN SELECT (...) and watch for errors, but is there a way to check for other commands as well?

Answer 1

Not without knowledge of the schema (for example, is 'x' a table?) and writing a SQL parser. Your MySQL query tool should be able to do that kind of validation (intellisense if you like) but I know from first hand experience, most of the (free) MySQL tools are abysmal.

'Preparing' the query would do what you want, but is a runtime check, not a compile time check - you seem to be looking for a compile time/offline solution.

Answer 2

To verify a query i use the EXPLAIN command. You can take any SQL query and add EXPLAIN before it and execute. If query is wrong, error will be returned.

Examples:

explain select * from users;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | SIMPLE      | users | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+

And wrong query

explain select * from users2;
ERROR 1146 (42S02): Table 'test.users2' doesn't exist

PS Explain works for insert, update, delete too. Not only select

Answer 3

Depending on your MySQL engine and settings, you could start a transaction, try the query, and then do a rollback. Assuming dirty reads are off, that should work.

Answer 4

You could create a temporary table to circumvent side effects of the query:

CREATE TEMPORARY TABLE users SELECT * FROM users;
INSERT INTO users(name) VALUES('UniqueName');
DROP TABLE users;
SELECT * FROM users WHERE name='UniqueName'; -- Should return 0 results

Answer 5

You can temporarily create a stored procedure with your code and unique name. Then you can drop it immediately. Transactions can't rollback SP creation. But be careful, because it just syntax validation, so it doesn't check if an object (in your query) exists or not.