If you need indexes, MySQL will EXPLAIN

Setting up indexes is essential to keeping your queries nice and quick.

Adding an index is easy – if you’re using phpMyAdmin, just find your table, click “Create an Index” and choose your column or columns.

Adding the right indexes is not easy and can be a bit hit-and-miss. This is where the handy EXPLAIN function comes in. Find your query that you want to optimise and add EXPLAIN to the beginning, as so:

EXPLAIN SELECT * FROM table;

This will give you output similar to:

id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE table ALL NULL NULL NULL NULL 67

If your “key” field is NULL, take a look at the table it is against and make sure any JOIN or ORDER BY in your query has an index.

Find more information in the MySQL manual.

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