Will SQL update affect its subquery during the update run?

Question

I\'m just composing a complex update query which looks more or less like this:

update table join
    (select y, min(x) as MinX 
     from table
     group by         


        

Answer 1

Although its been noted you SHOULDN'T be able to do an update to a table based on its own data, you should be able to adjust the MySQL syntax to allow for it via

update Table1, 
       (select T2.y, MIN( T2.x ) as MinX from Table1 T2 group by T2.y ) PreQuery
  set Table1.x = Table1.x - PreQuery.MinX
  where Table1.y = PreQuery.y

I don't know if the syntax goes a different route using JOIN vs the comma list version, but by the complete prequery you do would have to be applied first for its result completed ONCE, and joined (via the WHERE) to actually perform the update.