来自子查询中同一表的MySQL UPDATE和SELECT

Question

First off, I know this is impossible as of MySQL 5.1.x, it says so right here:

http://dev.mysql.com/doc/refman/5.1/en/update.html

What I'm asking though is if there is a clever way to execute a query using either a temporarily table/view without having to resort to writing a quick script to do the work. My query (which is COMPLETELY WRONG and DOES NOT work, just an FYI for folks trying this at home) looks something like this:

UPDATE some_table 
set some_col = ( SELECT some_othercol 
                 from some_table 
                 WHERE some_col > some_othercol
               );

I'm trying to ultimately set some_col to the value of some_othercol if sol_col > some_othercol .

What's the best way to handle this without resorting to a script?

EDIT My subquery returns more than one row!

Answer 1

I don't really understand why you need a subquery. Doesn't this do what you want?:

UPDATE some_table 
SET some_col = some_othercol 
WHERE some_col > some_othercol

Answer 2

I'm not sure if this is quite what you're trying to do, but maybe I can show you something to put you on the right path.

UPDATE some_table ST
SET some_col = (
    SELECT some_col
    FROM some_table OT
    WHERE OT.ID = ST.ID
)
WHERE ST.some_col > 2

That will set some_col to its own value, but only when some_col is already greater than 2. I know this doesn't do anything, but it shows a concept that may be closer to what you're looking for. If you give some more detail as to what you what to happen in the end, I can possibly help you find a solution closer to what you need.

Answer 3

http://www.xaprb.com/blog/2006/06/23/how-to-select-from-an-update-target-in-mysql/是我所知道的关于该主题的最佳资源。