Re: SQL Question

On 19 Dec 2012 14:29, Jeff Young wrote:

I want to use SQL to determine if a record exists in a file for a
given value.
There will be either only 1 record in the file for the value, or it
will not exist.

Given a variable [named CmpVal] that is compatible with the column [named TheCol] of the TABLE [named TheFile], then the following SQL embedded statement can be used:

D ind S 1A inz('?')
D* "ind" if Row Exists: '1'=True, '0'=False, '?'=InquiryFailed
exec sql
set ind=coalesce( (select '1'
from TheFile
where TheCol=:CmpVal)
, '0' ) ;

Of course like any SQL, the return code is best still checked, although in the above given setup, any failure of the statement yields '?' irrespective of the type of error. For example sqlcode=-811 if the uniqueness were not a valid assumption ¿and use of the FETCH FIRST ROW ONLY may not be not allowed for the scalar fullselect? Other errors could be file not found, column not found, selection\conversion data errors, etc. Using an indicator is an alternative, although then the test of the sqlcode or sqlstate is even more relevant, to know that a false result is due to an error versus due to no row being selected.

Or in an SQL procedure, perhaps:

/* ind inout char, cmpval in ... */
/* "ind" if Row Exists: '1'=True, Null=False, '?'=InquiryFailed
declare CONTINUE HANDLER for SQLEXCEPTION set ind = '?';
set ind=(select '1' from TheFile where TheCol=CmpVal) ;