fix(mysql): Fix AttributeError crash when transpiling IGNORE/RESPECT NULLS

[ShubhamKapoor992]

Fixes #7359

Description

Fixes a critical bug where MySQL dialect crashes with AttributeError when transpiling SQL containing IGNORE NULLS or RESPECT NULLS clauses in window functions.

Problem

When transpiling window functions with IGNORE NULLS or RESPECT NULLS from other dialects (e.g., Snowflake, DuckDB) to MySQL, the generator crashes with:

AttributeError: 'IgnoreNulls' object has no attribute 'sql_name'
AttributeError: 'RespectNulls' object has no attribute 'sql_name'

Root Cause

• MySQL has NULL_ORDERING_SUPPORTED = False, which triggers NULL ordering simulation logic
• The code in generator.py:ordered_sql() retrieves window.this to check window function properties
• However, window.this can be an IgnoreNulls or RespectNulls wrapper object (not the actual window function)
• The code attempts to call .sql_name() on these wrapper objects, which don't have that method

Example

python
import sqlglot

# This crashes before the fix
sql = "SELECT FIRST_VALUE(col1) IGNORE NULLS OVER (ORDER BY col2) FROM table1"
result = sqlglot.transpile(sql, read='snowflake', write='mysql')[0]
# AttributeError: 'IgnoreNulls' object has no attribute 'sql_name'

Solution

Added logic to unwrap IgnoreNulls and RespectNulls wrapper objects before accessing window function properties.

Changes

File: sqlglot/generator.py (lines 2857-2862)

if isinstance(window, exp.Window):
    window_this = window.this
    # Unwrap IgnoreNulls/RespectNulls wrappers to get the actual window function
    while isinstance(window_this, (exp.IgnoreNulls, exp.RespectNulls)):
        window_this = window_this.this
    spec = window.args.get("spec")

Testing

✅ All 1,059 existing tests pass (17,694 subtests)
✅ Tested across 9 database vendors (MySQL, Oracle, PostgreSQL, Snowflake, BigQuery, Redshift, Spark, Hive, DuckDB)
✅ No regressions introduced
✅ MySQL now successfully transpiles IGNORE/RESPECT NULLS without crashing

[geooo109]

Hello @ShubhamKapoor992 , thanks for the PR.
Let's also include tests for the fix.

[geooo109]

@ShubhamKapoor992 deleted the previous comments to make more clear what we should do at once, thanks.

[geooo109]

Nice work!

[ShubhamKapoor992]

Nice work!

@geooo109 Thank you. Any idea why the PR test fails

home/runner/work/sqlglot/sqlglot/sqlglot/generators/bigquery.py: error: Duplicate module named "sqlglot.generators.bigquery" (also at "/home/runner/work/sqlglot/sqlglot/sqlglot/generators/bigquery.py")

[geooo109]

@ShubhamKapoor992 nothing to worry about, I'm waiting for this #7381 and after I will merge.

[ShubhamKapoor992]

@ShubhamKapoor992 nothing to worry about, I'm waiting for this #7381 and after I will merge.

Thank you.