When does mysql use indexes?

The situations where indexes need to be used in MySQL include: when using a link that does not start with a wildcard, when extracting rows from a table when performing a join, and when finding the max or min value of a specified index, etc.

When does MySQL use indexes

1. Use >, >=, =, <, <= for a key code , IF NULL and BETWEEN

SELECT * FROM table_name WHERE key_part1=1 and key_part2 > 5;
SELECT * FROM table_name WHERE key_part1 IS NULL;

2. When using LIKE that does not start with a wildcard

SELECT * FROM table_name WHERE key_part1 LIKE 'jani%'

3. When extracting rows from another table when performing a join

SELECT * from t1,t2 where t1.col=t2.key_part

4. Find the MAX() or MIN() value of the specified index

SELECT MIN(key_part2),MAX(key_part2) FROM table_name where key_part1=10

5. Use ORDER BY or GROUP BY as the prefix of a key code

SELECT * FROM foo ORDER BY key_part1,key_part2,key_part3

6. Use it in all queries The column is part of the key code

SELECT key_part3 FROM table_name WHERE key_part1=1

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