--- In firebird-support@yahoogroups.com, Svein Erling Tysvær <svein.erling.tysvaer@...> wrote: > > >I have a table TableA with the following data: > > > >LINE USED > > 1 F > > 2 F > > 3 F > > 95 F > > 96 F > > > >and a table TableB with the following data: > > > >LINE > > 1 > > 2 > > 3 > > 4 > > > >and I need to put a 'T' on the USED column when the line's number is the > >same in both tables (in this case, when it is 1, 2 or 3). Of course, there > >are much more numbers and I dont know them. > > > >How I can make an update on TableA when it has the same numbers that TableB > >has? > > Hi Walter, > > UPDATE TableA TA > SET TA.USED = 'T' > WHERE EXISTS(SELECT * FROM TableB TB > WHERE TA.LINE = TB.LINE) > > Set >
Hi Set, Out of interest, does SELECT 1 work identically and if so whether it performs any quicker (if this were a very large table) than SELECT * in the sub-select? In other words, I'm unclear how the rows from the sub-select are 'materialised' prior to joining to TableA and whether * is needed return TB.LINE so as to test for TA.LINE = TB.LINE or not (if that makes sense!). e.g. UPDATE TableA TA SET TA.USED = 'T' WHERE EXISTS(SELECT 1 FROM TableB TB WHERE TA.LINE = TB.LINE) Thanks, Tom
