Will or be indexed in mysql?

In MySQL, whether an OR query uses an index depends on the following factors: index coverage, the order in which the index is selected, and the index type. To optimize OR queries, you can take the following steps: 1. Use a covering index; 2. Optimize index selectivity; 3. Use query rewriting; 4. Use multiple queries with UNION.

Whether OR queries in MySQL will use indexes

In MySQL, useORWhen conditions are met, whether to use an index depends on the following factors:

• Index coverage:If all fields in the query are in the index, the index is used. Otherwise, the index will not be used.
• The order of index selection:MySQL will select the index with the narrowest range for use. If multiple indexes cover a portion of the query's fields, the index with the greatest number of covered fields will be chosen.
• Index type:Only clustered indexes and unique indexes can be used forORqueries. Other types of indexes (such as ordinary indexes, full-text indexes) cannot be used forORqueries.

How to optimize OR query

In order to optimizeORquery, you can perform the following operations:

• Use a covering index:Ensure that all fields in the query are in the index.
• Optimize index selectivity:Create indexes on frequently used fields and use unique indexes to cover fields with unique values.
• Use query rewriting:For complex queries that contain multipleORconditions, you can try using query rewriting to restructure the query to make it more efficient.
• Use multiple queries with UNION:For very complexORqueries, you can split the query into multiple queries containingUNIONClause query to improve efficiency.

The above is the detailed content of Will or be indexed in mysql?. For more information, please follow other related articles on the PHP Chinese website!