结合更新和选择查询

Question

I got two MySQL working fine and i'm trying to find a way to combine them into one single query.

First, it selects ID of an employee.

SELECT 'ID' FROM `employee` ORDER BY ID DESC LIMIT 1;

Let's say it returns ID 100;

Then update data of employees whose ID is 100

UPDATE 'LOG' SET `TIME_EXIT`='2013/02/22' WHERE `ID`='100';

Can i do it all in a single query?

Answer 1

Just add them together:

UPDATE LOG SET TIME_EXIT = '2013/02/22' 
WHERE ID = (
              SELECT ID
              FROM employee
              ORDER BY ID DESC
              LIMIT 
            );

But based on that code currently it'll only ever update the last employee , you will need to select the correct employee by using some other identifier to ensure you have the correct one.

UPDATE LOG SET TIME_EXIT = '2013/02/22' 
WHERE ID = (
              SELECT ID 
              FROM employee 
              WHERE NAME = 'JOHN SMITH' 
              ORDER BY ID DESC 
              LIMIT 1
            );

Answer 2

It's now a few months old, but maybe helps you or others finding this via google…

If you want to UPDATE a field in the same selected table use this:

UPDATE LOG SET
    TIME_EXIT = '2013/02/22' 
WHERE ID = (
        SELECT ID
        FROM (
            SELECT ID
            FROM LOG
            WHERE whatEverYouWantToCheck = whateverYouNeed
        ) AS innerResult 
    )

So, you SELECT id from a subselect. If you try to subselect it directly, mySQL quites with your error message You can't specify target table 'log' for update in FROM clause , but this way you hide your subsubquery in a subquery and that seems to be fine. Don't forget the AS innerResult to avoid getting the error message #1248 - Every derived table must have its own alias . Also match the subsubquery field name to the subquery field name in case you do something like SELECT COUNT(*) or SELECT CONCAT('#', ID)