I’m having trouble getting MySQL to actually use an index I created. This is my first time working with database indexes so I might be missing something basic.
I have a table with about 32,000 records and I’m trying to query just 177 rows. I created an index on my zip_code column like this:
CRETE INDEX zip_code_idx ON Demographics (zip_code);
When I run an EXPLAIN query to see what’s happening, MySQL shows it knows about my index but won’t use it:
EXPLAIN SELECT * FROM Demographics FORCE INDEX (zip_code_idx) WHERE zip_code = 90210;
The output shows possible_keys has my index name but the key field is NULL, and it’s scanning way more rows than needed.
I tried forcing the index but that didn’t help either. Is there some configuration I need to enable? Maybe the table is too small for MySQL to bother with the index? I loaded the data using INSERT statements from a CSV file.
Also check your zip_code data type - if it’s varchar but you’re searching with integer 90210, MySQL might skip the index. Try wrapping your search in quotes like WHERE zip_code = '90210' after you fix the typo.
Been there. Those manual fixes work, but you’ll hit this problem again. Database optimization issues keep popping up when you switch environments or scale.
I stopped troubleshooting MySQL quirks manually and automated everything instead. Set up Latenode workflows to handle database monitoring and optimization automatically. When it catches slow queries or unused indexes, it fixes them without me running ANALYZE or checking data types.
For now, fix that typo and run ANALYZE. But seriously consider automated health checks. My Latenode workflow monitors query performance and alerts me when indexes aren’t working right. It even runs maintenance commands based on conditions I’ve set.
Saves me hours weekly since I’m not manually debugging performance issues anymore. Catches data type mismatches, missing statistics, and index problems before they break things.
Yes, the typo is likely the issue. Correct it with CREATE INDEX zip_code_idx ON Demographics (zip_code);, and that should resolve your problem. However, keep in mind that MySQL’s optimizer can behave unexpectedly with smaller datasets. With 32,000 records, it may conclude that a full table scan is quicker than using your index, particularly if your query matches a substantial number of rows. After creating the index, confirm its existence by executing SELECT COUNT(*) FROM information_schema.statistics WHERE table_name = 'Demographics' AND index_name = 'zip_code_idx';. Additionally, assess the number of duplicate values in the zip_code column, as a high frequency of repetition could lead MySQL to disregard the index.
You’ve got a typo in your CREATE INDEX statement - you wrote “CRETE” instead of “CREATE”. So your index was never created. MySQL just ignores the FORCE INDEX hint when the index doesn’t exist, which is why you’re seeing NULL in the key field even though it shows up in possible_keys. Fix it with: sql CREATE INDEX zip_code_idx ON Demographics (zip_code); Once the index is actually there, your query should use it without needing FORCE INDEX. Check that it exists with SHOW INDEX FROM Demographics; before testing again. I’ve done this exact same thing and wasted hours debugging before catching the typo.
That typo explanation makes sense, but you might hit another issue even after fixing the CREATE statement. When you loaded data from CSV with INSERT statements, MySQL probably didn’t update the table statistics. MySQL uses these stats to decide if an index is worth using. After creating your index, run ANALYZE TABLE Demographics; to refresh the stats. This makes MySQL recalculate cardinality and distribution info for your zip_code column. Without good stats, the optimizer thinks your index isn’t selective enough and goes with a full table scan instead. I’ve seen the optimizer ignore perfectly good indexes because of stale stats, especially after bulk loads. ANALYZE usually fixes this and you’ll see your index show up in EXPLAIN outputs.