November 17, 2009 at 4:01 am
While executing the following commands
-- Set 1
alter table employee add test varchar(10)
update employee set test = 'abc'
go
I get the error
"Invalid column name 'test'"
The following works fine....
-- Set2
alter table employee add test varchar(10)
go
update employee set test = 'abc'
go
But now, if I drop the column using
-- Set 3
alter table employee drop column test
go
and try to execute Set 1 that is,
alter table employee add test varchar(10)
update employee set test = 'abc'
go
I don't get the error I was getting before. Why?
November 17, 2009 at 5:32 am
Schema evaluation happens during parsing time, not execution time (just like in any other programming language).
So, there is nothing stange in this behaviour.
P.S. Altering table schema on fly is one of the worst practices known in database development.
Avoid it by any means.
If you are absolutely sure it's the only way to go ask some some experienced DB developer how to build a correct solution.
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Code for TallyGenerator
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