>>how do u write a derived field in sql tablesee below>>if a foreign key is being used as a primary key in another table, do u have to set it to NOT NULL ?no - see belowHere are 3 simple examples. A computed column, a derivedResultSet column and a nullable foreign key.use pubsset nocount on--create a table with a derived columncreate table junk (i int primary key, derivedCol as i+1)goinsert junk (i) values (1)select * from junkgo--create a table with a nullable foreign keycreate table junk2 (rowid int identity(1,1), i int null references junk(i))goinsert junk2 (i) values (null)insert junk2 (i) values (1)goselect i, derivedCol, derivedCol-i as derivedResultSetColumn from junkselect rowid, i from junk2godrop table junk2drop table junk
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