Office Apps Freezing

Fix Microsoft Access Query Freezing with Complex WHERE Conditions

Maira Mehtab Sep 22, 2026 870 views

Question details

The user needs to resolve an issue where a previously working MS Access query now runs for hours or hangs completely when processing multiple criteria.

Product: Microsoft Access
Device & OS: not provided
Scenario: Running a VBA-driven query containing complex AND/OR WHERE conditions against a database whose dataset has likely grown over time.
Observed behavior: The single complex query freezes or takes hours to execute, but manually splitting the criteria into four separate queries joined by UNION produces the desired results quickly.

Before you start

Before making structural changes to your database or modifying complex VBA queries, ensure you create a backup copy of your Access database (.accdb or .mdb) to prevent accidental data loss.

Solution 1Recommended

Optimize Query Execution and Database Indexes

Improve overall query performance by validating data types, adding missing indexes, and ensuring logical criteria are structured efficiently.

As a database grows, queries that once performed well can suddenly bottleneck. This often occurs when complex SQL logic forces the database engine to scan entire tables instead of utilizing indexes.

Test with a restricted dataset

Temporarily add a limiting condition (like a date range or specific ID threshold) to your WHERE clause to confirm if the freeze is purely caused by data volume.

Review table indexes in Design View

Open your tables in Design View and ensure that all fields used in your JOIN clauses and WHERE conditions have the 'Indexed' property set to 'Yes (Duplicates OK)' or 'Yes (No Duplicates)'.

Verify logical grouping

Check your SQL view to ensure parentheses () around your AND and OR expressions are correctly placed. Misplaced parentheses can cause Access to evaluate massive, unintended record combinations.

Match data types across joins

Ensure that fields being compared or joined across different tables share the exact same data type and field size, as mismatched types force Access to perform slow row-by-row conversions.

Solution 2

Refactor the Complex Query into UNION Queries

Split complex OR logic into multiple simpler queries joined by a UNION operator to help the Access database engine process the data faster.

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Frequently Asked Questions

Why did my Access query suddenly start freezing after months of working fine?

Queries usually start freezing when the underlying dataset grows past a certain threshold. More records mean the database engine has to evaluate complex AND/OR conditions across a larger volume. If indexes are missing, this exponentially increases execution time and causes the application to hang.

How do I know if my Access tables need indexing?

If your query involves searching, sorting, or joining on specific fields (especially those heavily used in your WHERE clause) and it runs slowly, those fields likely need indexes. You can add them in the Table Design view by setting the 'Indexed' property to 'Yes'.

Is UNION always faster than complex OR conditions in Access?

Not always, but the Access database engine (JET/ACE) sometimes struggles to build an efficient execution plan for complex OR logic in a single pass. Splitting it into UNION queries forces the engine to run simpler, highly optimized searches and then combine the results, which often resolves freezing.

Can incorrect parentheses cause a query to hang indefinitely?

Yes. If parentheses are missing or misplaced in a WHERE clause that mixes both AND and OR operators, Access might interpret the logic incorrectly. This can cause the engine to evaluate a massive, unintended number of record combinations (similar to a Cartesian product), leading to severe freezing.

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