I am trying to write a stored procedure that involves a lot of case when statements. I have a condition(when y=1, 10 more if conditions inside it), similarly for y=2 and y=3. I was trying to see if it could be simplified.
well, my application page has a drop down list with 3 options when i select either one of that, then i had a choice to select another 10 options in separate drop down list. So, i am trying to call my stored procedures in that page. thanks.
set #where = case
when #y = 1
then
case
when #value=1
then
//do something
else # value =2
then
//do something
... repeat then statement 8 more times
when #y=2
//10 time check conditions
when # y =3
//repeat again with #value condition 10 times
end
Related
I have a SELECT statement from a temp table in a stored procedure that selects these two columns:
DECLARE #Mode INT
CASE
WHEN t.Descr = '-- Prior Balance --'
THEN ''
ELSE t.ChgAmount
END AS ChgAmount,
CASE
WHEN t.Descr = '-- Prior Balance --'
THEN ''
ELSE t.PayAmount
END AS PayAmount,
I want to conditionally return those two columns differently depending on the value of #Mode, specifically if it is equal to 7.
I'm getting confused about the levels of nesting that I need and the formatting of doing this.
So far I have tried something like this:
CASE
WHEN #Mode = 7
THEN
CASE
WHEN t.TranDate > #Due
THEN t.ChgAmount
END
END AS CurrentCharges,
CASE
WHEN t.Descr = '-- Prior Balance --'
THEN ''
ELSE t.ChgAmount
END AS ChgAmount,
CASE
WHEN t.Descr = '-- Prior Balance --'
THEN ''
ELSE t.PayAmount
END AS PayAmount,
The above SELECT might work, but it would stil return the extra column. How should I nest the other, original, CASE statement for the ChgAmount?
First, let's clarify in abstract terms that in the following pseudo-code
If X then
Case 1
If Y then
Case 2
Else
Case 3
End If
Else
Case 4
End If
Case 1 is equivalent to "X is true"
Case 2 is equivalent to "X is true and Y is true"
Case 3 is equivalent to "X is true and Y is false"
Case 4 is equivalent to "X is false"
Furthermore, let's clarify that case-when criterias are logically very similar to our pseudo-code presented above of if-then, hence, you can apply composite criteria instead of nesting case-when if you prefer that, but also, you can implement nested case-when criterias, it's a matter of style.
As a result, you will need to formulate the logic you want to apply, by asking yourself the following questions:
do I need the same number of fields in my different cases? (if not, then you will probably need to write different queries in different cases)
what cases do I have for my fields if #Mode is 7?
what cases do I have for my fields if #Mode is not 7?
how can I merge my criterias in the points above into coherent (composite) criterias that would not require nesting?
If you answer these questions as an edit to this question, then we will be able to more properly answer your questions than the general terms I'm using in this answer and we may provide code for you as well. However, if you think this through, then you might also be able to implement this in a not nested way. And, if you are able to understand this as far as to implement it into a not nested way, then you could transform that implementation into a nested implementation as well.
I've been looking over some code in an old Classic ASP system of ours that builds its own SQL within the stored procedure and then executes it {shudders}.
Several of the SELECTion lines contain an assignment, similar to:
SELECT
my_field = CASE WHEN value = whatever THEN 1 ELSE 0 END
...
Is there any difference (or anything I need to be aware of) between this and using a standard AS alias?...
SELECT
CASE WHEN value = whatever THEN 1 ELSE 0 END AS my_field
...
No, the following code is all synonymous:
SELECT one = 1;
SELECT 1 one;
SELECT 1 AS one;
SELECT 'one' = 1; --this is deprecated, don't use it.
Which you use (apart from the last), is normally down the preference. Personally, I use AS. One reason is I can then easily tell queries that return datasets, and those that assign values to variables a part.
The 2 examples that you have given are identical. However, when you go through the old code you might also find a variant with an # sign before my_field, like this:
SELECT
#my_field = CASE WHEN value = whatever THEN 1 ELSE 0 END
In this case a varable called #my_field is assigned a value, but nothing is SELECTed. This you can not rewrite to the other syntax using AS #myfield.
I have been assigned the task of updating the EEO survey and reporting for a mid sized company. I am working on a stored procedure to populate a report from. All is good but for a syntax problem. One of the requirements is to dynamically allow the user to filter the results by the EEO Job Group Number. When the report page loads, it populates the table with all Job Groups Combined. I have placed a DropDownList on the page that allows the user to choose one of the 10 EEO Job Groups or by default, All Job Groups Combined (no filtering). The DDL executes postback and populates a parameter; #intEeoJobGroupID. There is not actually a 0 ID value in the table, just in the DDL. I want the (usp) query to use one set of WHERE statements if the passed parameter #intEeoJobGroupID = 0, and another if #intEeoJobGroupID <> 0. (Effectively adding another AND statement if the parameter <> 0)
I want to return the count of how many EEO records meet the requirements of the query. I have tried IF/THEN, and CASE, in many different formats, and can not seem get the syntax right. In the example below I get the message "Incorrect Syntax near the first = in the THEN statement, as well as the keyword ELSE.
Any hints?
DECLARE #intEeoJobGroupID INT
SELECT
COUNT (E.intEeoID)
FROM
dbo.NewEEO AS E
WHERE
CASE WHEN #intEeoJobGroupID = 0
THEN
E.intGenderID = 1
AND E.intRaceID = 2
ELSE
E.intGenderID = 1
AND E.intRaceID = 2
AND E.intEeoJobGroupID = #intEeoJobGroupID
You're making it way too complicated:
WHERE E.intGenderID = 1
AND E.intRaceID = 2
AND (E.intEeoJobGroupID = #intEeoJobGroupID OR #intEeoJobGroupID = 0)
As someone else already mentioned, your existing syntax was missing an "END", but it still won't work with that added. To get this right in the future, one thing you can try to do is remember that CASE expressions in SQL are just that: expressions. They are not statements, as you might be used to with if statements in c# code. You don't use CASE for flow control, to define blocks as you were trying to do.
Don't try to return a boolean from a CASE statement. Instead return some value that is then checked outside the CASE statement (and so then resulting in a boolean).
CASE WHEN #mode = 1 THEN CASE WHEN <Condition1> THEN 1 ELSE 0 END
WHEN #mode = 2 THEN CASE WHEN <Condition2> THEN 1 ELSE 0 END
END
=
1
Note: This will create Awful execution/explain plans and totally nerf performance. You are better using real IF blocks and real queries, or possibly unions...
IF #mode = 1
SELECT foo FROM bar WHERE <Condition1>
ELSE IF #mode = 2
SELECT foo FROM bar WHERE <Condition2>
Or...
SELECT foo FROM bar WHERE <condition1> AND #mode = 1
UNION ALL
SELECT foo FROM bar WHERE <condition2> AND #mode = 2
In order to prevent massive duplication of code, you may find that encapsulating the bulk of the query in a VIEW is helpful.
You can't make a comparison the result of a case condition. If you're using case in a where clause, it needs to be on one side of the operator:
CASE #case_value
WHEN 0 THEN
some_column
ELSE
some_other_column
END = #some_value
However, if you try to make your actual condition fit this rule, you'll end up not using the case statement at all, as #Joel point out.
You have to add
end
in the end of case.
If you have 100 occurrences of "PRINT" in your stored procedure, is there a nice way to turn them all on/off when debugging an non-debugging?
I could add a variable #isdebug = 1
and later on, do something like
IF #isdebug = 1 PRINT #yourvar
and then just set the #isdebug to 0 or 1 depending on what you need.
Is there a nicer way to do this?
Nope, that is also what I have in procs
IF #debug = 1
BEGIN
print 'Something'
--or insert into a log table if you need the rows of a temp table
--or the results of a calculation
END
An expansion of this idea is to setup up a controlling string. This giving us more options rather than either on or off.
For example:
Stored procedure parameter declaration
(#Debug varchar(5), -- use bit wise control for debugging, currently 5 levels.
Simple substring to drive a testing/debug block.
if substring(#Debug, 1, 1) = '1'
For a test run you could enter '10001' for #Debug so that "level" 1 debugs show (ie initialisations) and only "level" 5 debugs show for the sub-section of code you are testing/debugging.
You could expand on this idea by using number values (ie 2-9) too. But that might be too over the top.
I need to branch my T-SQL stored procedure (MS SQL 2008) control flow to a number of directions:
CREATE PROCEDURE [fooBar]
#inputParam INT
AS
BEGIN
IF #inputParam = 1
BEGIN
...
END
ELSE IF #inputParam = 3
BEGIN
...
END
ELSE IF #inputParam = 3
BEGIN
...
END
END
Is there any other ways? For example, in C# I shoud use switch-case block.
IF...ELSE... is pretty much what we've got in T-SQL. There is nothing like structured programming's CASE statement. If you have an extended set of ...ELSE IF...s to deal with, be sure to include BEGIN...END for each block to keep things clear, and always remember, consistent indentation is your friend!
Also you can try to formulate your answer in the form of a SELECT CASE Statement. You can then later create simple if then's that use your results if needed as you have narrowed down the possibilities.
SELECT #Result =
CASE #inputParam
WHEN 1 THEN 1
WHEN 2 THEN 2
WHEN 3 THEN 1
ELSE 4
END
IF #Result = 1
BEGIN
...
END
IF #Result = 2
BEGIN
....
END
IF #Result = 4
BEGIN
//Error handling code
END
No, but you should be careful when using IF...ELSE...END IF in stored procs. If your code blocks are radically different, you may suffer from poor performance because the procedure plan will need to be re-cached each time. If it's a high-performance system, you may want to compile separate stored procs for each code block, and have your application decide which proc to call at the appropriate time.
The Transact-SQL control-of-flow language keywords are:
BEGIN...END
BREAK
CONTINUE
GOTO label
IF...ELSE
RETURN
THROW
TRY...CATCH
WAITFOR
WHILE
Nope IF is the way to go, what is the problem you have with using it?
BTW your example won't ever get to the third block of code as it and the second block are exactly alike.
CASE expression
WHEN value1 THEN result1
WHEN value2 THEN result2
...
WHEN valueN THEN resultN
[
ELSE elseResult
]
END
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