Обсуждение: Order of execution
I have an UPDATE query which performs several opertions in one table.
UPDATE table01 SET
field1 = (query1 may contain any field),
field2 = (query1 may contain any field),
field3 = (query1 may contain any field)
WHERE (condition)
query1, query2 and query3 perform a logic to determine which records will be updated. Does field1 updates first, then field2 and, lastly, field3? or What is the order in which updates are executed? If I need fields to be updated in a certain order, should I use 3 UPDATE commands instead?
Respectfully,
Jorge Maldonado
On 2013-05-06, JORGE MALDONADO <jorgemal1960@gmail.com> wrote: > --089e013d1eb83325e504dc01710d > Content-Type: text/plain; charset=ISO-8859-1 > > I have an UPDATE query which performs several opertions in one table. > > UPDATE table01 SET > field1 = (query1 may contain any field), > field2 = (query1 may contain any field), > field3 = (query1 may contain any field) > WHERE (condition) > > query1, query2 and query3 perform a logic to determine which records will > be updated. Does field1 updates first, then field2 and, lastly, field3? Updates are one row at a time in an unpredictble order. this will be wrapped in a transaction so either all will updated or none. testing suggests that in simple cases the expressions are evaluated in the order the columns appear in the table definition, but I wouldn't rely on that. > or What is the order in which updates are executed? If I need fields to be > updated in a certain order, should I use 3 UPDATE commands instead? yeah, if "simultaneously" isn't acceptable you'll need to do separate updates. -- ⚂⚃ 100% natural