SQL Index Optimization: Make Queries 100x Faster
How database indexes work, when to add them, composite indexes, covering indexes, and common indexing mistakes.
When to Index
- Columns in WHERE clauses
- Columns in JOIN conditions
- Columns in ORDER BY
- High-cardinality columns (many unique values)
When NOT to Index
- Small tables (<1000 rows)
- Columns with low cardinality (boolean, status)
- Tables with heavy INSERT/UPDATE (indexes slow writes)
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