Throw and catch
The following example creates the
procedure tq84_check_percentage which takes one argument (
@percentage). The procedure then verifies if the value of this argument is between 0 and 100. If not, it reports this to the caller using a
throw statement.
The procedure is then called called in a block that is embedded in begin try … end try which allows to be notified of a such exception in the following begin catch … end catch.
The
catch block then uses the function
error_message which returns the text that was used in the
throw statement.
create procedure dbo.tq84_check_percentage
@percentage float
as begin
if @percentage < 0 begin
throw 50000, 'Percentage must be greater than 0.', 1;
end;
if @percentage > 100 begin
throw 50000, 'Percentage must be smaller than 100.', 1;
end;
print('OK: ' + str(@percentage));
end
go
begin try
exec tq84_check_percentage 9;
exec tq84_check_percentage 42;
--
-- Following line causes throw to be executed which
-- is caught below in `begin catch`.
--
exec tq84_check_percentage 123;
--
-- Following line is not reached (because line above
-- causes throw).
--
exec tq84_check_percentage 17;
end try
begin catch
print(error_message());
end catch
go
--
-- Output:
--
-- OK: 9
-- OK: 42
-- Percentage must be smaller than 100.