fix(optimizer): enhance simplify_parens to handle additional parent t…

[MuSilk]

Fixes #7338

Problem

The sqlglot.optimizer.simplify.simplify_parens() function incorrectly removes parentheses around a comparison (exp.Predicate) when it is used as an operand in an arithmetic expression.
In dialects like MySQL, boolean results are treated as integers (0 or 1). Consequently, an expression like a - (b < c) is valid and meaningful. However, the current optimizer logic only checks if the parent is exp.Neg before preserving parentheses for predicates. It fails to account for other binary arithmetic operators (Add, Sub, Mul, etc.).
This leads to incorrect SQL generation where operator precedence is altered, changing the logic of the query.
Reproduction
Input SQL:

SELECT * FROM A WHERE a - (b < c) >= 0

Current Incorrect Output:

SELECT * FROM A WHERE a - b < c >= 0

-- Parentheses around (b < c) are dropped incorrectly
-- This changes precedence: subtraction happens before comparison
SELECT * FROM A WHERE a - b < c >= 0
Note: a - b < c >= 0 is logically equivalent to (a - b) < c AND c >= 0 (depending on dialect chaining rules), which is completely different from a - (result_of_comparison) >= 0.

Root Cause

In sqlglot/optimizer/simplify.py, the simplify_parens function contains a condition:

isinstance(this, exp.Predicate) and not (parent_is_predicate or isinstance(parent, exp.Neg))

This logic assumes that only Neg requires parentheses around a predicate, ignoring binary arithmetic operators where the predicate acts as a numeric term.

Solution

Expand the check to include all binary arithmetic operators that have higher or equal precedence implications when a predicate is cast to a number. The fix adds exp.Add, exp.Sub, exp.Mul, exp.Div, exp.Mod, and exp.Pow to the exclusion list.

[VaggelisD]

Hey @MuSilk, thank you for the fix! I could repro this in MySQL:

# Parentheses
mysql> SELECT 0 - (1 < 2) >= 0;
0


# Simplified
mysql> SELECT 0 - 1 < 2 >= 0;
1

Leaving a couple of comments:

[VaggelisD]

We should instance-check against exp.Binary instead of each one individually e.g isinstance(parent, exp.Neg, exp.Binary)

[VaggelisD]

Can we also add tests in simplify.sql that exercise a couple of these paths? Even something simple as SELECT * FROM A WHERE a - (b < c) >= 0 AND a + (b < c) >= 0