Suggest an editImprove this articleRefine the answer for “How does an index affect insert and update speed?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)An index **speeds up reads**, but **slows down inserts and updates**: when an `INSERT`, `UPDATE`, or `DELETE` runs, the database not only has to change the data in the table, it also has to **update every index** that field is part of. **Key point:** if there's an index on `email` and `UPDATE users SET email = ... WHERE id = 1` runs, the database changes `email` in the table **and** rebuilds the value in the index - so `SELECT` gets faster with an index, while `INSERT`/`UPDATE`/`DELETE` get slightly slower.Shown above the full answer for quick recall.Answer (EN)ImageAn index **speeds up reads**, but **slows down inserts and updates**. ### Why When an `INSERT`, `UPDATE`, or `DELETE` runs, the database not only has to change the data in the table, it also has to **update every index** that field is part of. ### Example If there's an index on `email`, and this runs: ```sql UPDATE users SET email = 'new@mail.com' WHERE id = 1; ``` the database changes `email` in the table **and** rebuilds the value in the index. ### Summary - `SELECT`: faster with an index, - `INSERT`, `UPDATE`, `DELETE`: slightly slower, because indexes require **extra write operations**.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.