Question

This query will be done in a cached autocomplete text box, possibly by thousands of users at the same time. What I have below works, bit I feel there may be a better way to do what I am doing.

Any advice?

UPDATED — it can be ‘something%’:

SELECT a.`object_id`, a.`type`, 
    IF( b.`name` IS NOT NULL, b.`name`,
        IF( c.`name` IS NOT NULL, c.`name`, 
            IF( d.`name` IS NOT NULL, d.`name`,
                IF ( e.`name` IS NOT NULL, e.`name`, f.`name` )
            )
        )
    ) AS name
FROM `user_permissions` AS a 
   LEFT JOIN `divisions` AS b 
       ON ( a.`object_id` = b.`division_id` 
           AND a.`type` = 'division' 
           AND b.`status` = 1 ) 
   LEFT JOIN `departments` AS c 
       ON ( a.`object_id` = c.`department_id` 
           AND a.`type` = 'department'  
           AND c.`status` = 1 ) 
   LEFT JOIN `sections` AS d 
       ON ( a.`object_id` = d.`section_id` 
           AND a.`type` = 'section'  
           AND d.`status` = 1 ) 
   LEFT JOIN `units` AS e 
       ON ( a.`object_id` = e.`unit_id` 
           AND a.`type` = 'unit'  
           AND e.`status` = 1 ) 
   LEFT JOIN `positions` AS f 
       ON ( a.`object_id` = f.`position_id` 
           AND a.`type` = 'position'  
           AND f.`status` = 1 ) 
WHERE a.`user_id` = 1 AND ( 
    b.`name` LIKE '?%' OR
    c.`name` LIKE '?%' OR
    d.`name` LIKE '?%' OR
    e.`name` LIKE '?%' OR
    f.`name` LIKE '?%'
)

Answer 1

Other than changing the nested Ifs to use a Coalesce() function (MySql has Coalesce() doesn’t it)? There is not much you can do as long as you need to filter on that input parameter with a like expresion. Putting a filter on a column using a Like expression, where the Like parameter has a wildcard at the begining, as you do, makes the query argument non-SARG-able, which means that the query processor must do a complete table scan of all the rows in the table to evaluate the filter predicate.

It cannot use an index, because an index is based on the column values, and with your Like parameter, it doesn’t know which index entries to read from (since the parameter starts with a wild card)

if MySql has Coalesce, you can replace your Select with:

SELECT a.`object_id`, a.`type`,
Coalesce(n.name, c.name, d.Name, e.Name) name

If you can replace the search argument parameter so that it does not start with a wildcard, then just ensure that there is an index on the name column in each of the tables, and (if there are not indices on that column now), the query performance will increase enormously.