MySQL index --01--- design principle of index

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MySQL8.0 Index new features

2.1 Support descending index

2.2 Hide index

Which situations are suitable for creating indexes

1. There is a limit to the uniqueness of field values

2. Frequent act WHERE The field of the query condition

3. often GROUP BY and ORDER BY The column of

4. UPDATE、DELETE Of WHERE Conditional column

5. DISTINCT Fields need to be indexed

6. Multiple tables JOIN Connection operation , Precautions for index creation

7. Use the type of column to create a small index

8. Create an index using a string prefix

9. High discrimination ( High hashability ) The column of is suitable as an index

10. The most frequently used columns are placed on the left side of the federated index

When multiple fields need to be indexed , Joint index is better than single value index

Limit the number of indexes

Which situations are not suitable for index creation

1. stay where Fields not used in , Don't set the index

2. It is better not to use index for tables with small data volume

3. Don't build indexes on columns with a lot of duplicate data

4. Avoid creating too many indexes on frequently updated tables

5. Unordered values are not recommended as indexes

6. Delete indexes that are no longer or rarely used

7. Do not define redundant or duplicate indexes