> In another language I would do: > find first Order where Order.Order_num = "1111". > if avaialble Order then it_exists = true. > > In PostgreSQL ?: > SELECT DISTINCT Order_num from Order_header where Order_num = '1111'; > > Is this close? If so, how to raise flage that row exists? > > > How we do somthing like this in SQL?
Since you don't care about a value, just pull TRUE and use LIMIT to restrict to a single entry (much faster than DISTINCT, but not as portable). SELECT TRUE FROM Order_header where Order_num = '1111' LIMIT 1; Do a count of the number of rows returned. 1 row means it exists, 0 rows means it does not exist. It seems to me like you intend to insert a row with that number shortly after? You should be aware that this process will introduce a race condition (may not exist during test, but does exist shortly after during insert). If Order_num is Distinct on that table (or another), just try the insert. If it fails, increment the number and try again. If you don't mind gaps in the numbers, then a sequence will fare much better (easier and faster).
signature.asc
Description: This is a digitally signed message part
