How to use a SQL Function with INNER JOIN in MySQL?

问题

I have a function "fnc_FindIssueId" which accepts an object id and return its assigned issue Id.

When I call the function using pure select statements, it works fine:

select fnc_FindIssueId(150083); // returns 1 as issueId for objectId of 150083
select fnc_FindIssueId(150072); // returns 2 as issueId for objectId of 150072

But when I use it within an Inner Join, it goes into a never-ending loop:

select so.id, si.id
from smart_objects as so 
       LEFT OUTER join smart_issues as si 
        on si.id = fnc_FindIssueId(so.id)
where so.id in (150083, 150072);

What's the reason and how to resolve it?

回答1:

It does not perform never-ending loop.

The reason for that is because the server performs FULL TABLE SCAN which is very slow. This condition si.id = fnc_FindIssueId(so.id) doesn't use an index even if you have define one on si.id and so.id.

The best ways you can do are:

• to alter the table smart_objects
• another column for the assigned issue Id
• define an index on the new column

回答2:

The workaround was to create a new view with ObjectId and IssueId columns then calling that function from within that view! but it has become very slow now.

CREATE ALGORITHM=UNDEFINED DEFINER=`mysql`@`%` SQL SECURITY DEFINER VIEW `vw_smart_objectissue` AS select `so`.`id` AS `objectid`,`fnc_FindIssueId`(`so`.`id`) AS `issueid` from `smart_objects` `so` order by `so`.`id`$$

来源：https://stackoverflow.com/questions/14811363/how-to-use-a-sql-function-with-inner-join-in-mysql