Bug: SQL logic error in MySQL Storage due to missing parentheses in WHERE clause

[xiluoduyu]

Steps to reproduce

When using watermill-sql with MySQL and a custom GenerateWhereClause that contains an OR condition (e.g., for delayed messages), the final SQL query logic becomes corrupted because AND has higher precedence than OR.

Example Scenario:

• Base condition: acked = 0
• Dynamic condition: delayed_until <= NOW() OR delayed_until IS NULL

The generated SQL currently looks like:

SELECT ... WHERE acked = 0 AND delayed_until <= NOW() OR delayed_until IS NULL

Expected behavior

The dynamic condition should be wrapped in parentheses to maintain logical integrity:

SELECT ... WHERE acked = 0 AND (delayed_until <= NOW() OR delayed_until IS NULL)

Actual behavior

The SQL is interpreted as (acked = 0 AND delayed_until <= NOW()) OR (delayed_until IS NULL).

This causes messages where delayed_until IS NULL to be picked up even if they are already acked (acked = 1). This leads to infinite message duplication and high database load, as the same message is processed over and over again.

Possible solution

I have already submitted a fix here: ThreeDotsLabs/watermill-sql/pull/58.

This is a critical logic bug affecting data consistency in MySQL-based queues. Please consider reviewing the linked PR.