CASE WHEN ... THEN - sql

Question

I'm trying to edit a code someone wrote some months ago, but I can't understand some parts, for example:
CASE
WHEN #PROMPT('SEL_TYPE')# = '%' then 1
WHEN #PROMPT('SEL_TYPE')# = 'ALL' then 1
WHEN e.evt_job = #PROMPT('SEL_TYPE')# then 1
ELSE 0
END = 1
Wherever I read about how CASE .. WHEN works, it's like:
CASE A
WHEN 'ok' THEN C = 'ok'
WHEN 'bad' THEN C = 'bad'
But im my example it's just THEN 1 or ELSE 0.
Whats the meaning of that 1 or 0? It's something I'm missing on the code, or that 1 or 0 means something?
Thanks all, and sorry for my English :)

Answer 1

You should understand the difference between the CASE expression and the CASE statement. This is a CASE expression:
CASE
WHEN #PROMPT('SEL_TYPE')# = '%' then 1
WHEN #PROMPT('SEL_TYPE')# = 'ALL' then 1
WHEN e.evt_job = #PROMPT('SEL_TYPE')# then 1
ELSE 0
END = 1
This is an incomplete CASE statement (Supported by other databases, like Oracle or MySQL, but not SQL Server):
CASE A
WHEN 'ok' THEN C = 'ok'
WHEN 'bad' THEN C = 'bad'
An expression is something that can be evaluated on the right hand side of an assignment, or in a SELECT statement, for instance.
A statement is a command that can be used in an imperative language, i.e. in a stored procedure. The CASE statement (if supported by a database) works just like an IF statement.

Answer 2

It means someone has overcomplicated things. If SQL Server had a boolean data type, they'd probably have just had then true, else false and no comparison at the end. But because that's not possible in SQL Server, they've substituted 1 and 0 and then just compare that to 1 at the end to make it a logical comparison.
It could equally have been written as:
#PROMPT('SEL_TYPE')# = '%' OR
#PROMPT('SEL_TYPE')# = 'ALL' OR
e.evt_job = #PROMPT('SEL_TYPE')#
With no need for a CASE expression at all.
Or even, probably, as just #PROMPT('SEL_TYPE')# IN ('%','ALL',e.evt_job), but some may feel that this obscures the intent a little too much.
So,
select code, wo_num, desc from table1
where org = #PROMPT('SEL_ORG')# and
CASE
WHEN #PROMPT('SEL_WO_TYPE')# = '%' then 1
WHEN #PROMPT('SEL_WO_TYPE')# = 'ALL' then 1
WHEN e.evt_jobtype = #PROMPT('SEL_WO_TYPE')# then 1 ELSE 0 END = 1
and e.evt_type in (''A,'B')
Could have more simply been written as:
select code, wo_num, desc from table1
where org = #PROMPT('SEL_ORG')# and
e.evt_type in (''A,'B') and
(
#PROMPT('SEL_TYPE')# = '%' OR
#PROMPT('SEL_TYPE')# = 'ALL' OR
e.evt_job = #PROMPT('SEL_TYPE')#
)
Someone wrote a CASE expression (and then had to introduce the 1s and 0s) when all they needed was basic boolean logic.