WordPress - SQL 查询优化

Question

Is it better to add the condition (meta_key = 'items') to my query or this is not necessary.

I told myself that by limiting the research to only if meta_key equal to items will optimize my SQL Query.

global $wpdb;
$value = 'my_vaue';     
$result = $wpdb->get_results("SELECT * FROM wp_usermeta WHERE (meta_key = 'items') AND (meta_value LIKE '%%$value%%')");

Thanks!

Answer 1

This is your query:

SELECT *
FROM wp_usermeta
WHERE meta_key = 'items' AND
      meta_value LIKE '%%$value%%';

(Why do you have two '%' in the pattern? That is equivalent to one.)

Your question is not one of performance, but of functionality. The alternative is:

SELECT *
FROM wp_usermeta
WHERE meta_value LIKE '%%$value%%';

The first searches through the "items" for your value. The second searches through all rows in the table. Use the one that best matches the functionality you want.

Unless "items" are very rare in the table, both queries will do a full table scan. The performance will probably be dominated by reading the data. However, like is a bit expensive so the first version might be a wee bit faster.