How can I set a conditional filter in a SQL WHERE clause? For example, I have a parameter #ID with the following procedure
SELECT * FROM myTable WHERE Column1 = 'test' AND Column2 = #ID
However, If #ID = -1 I don't want the last part of the SQL (AND Column2 = #ID) included
I realize I can make an if statement with 2 separate queries, however this is a large script and has this same issue multiple times, so I was hoping there was a better way than nearly duplicating several queries
This is ok for T-SQL:
SELECT * FROM myTable WHERE Column1 = 'test' AND (#ID = -1 OR Column2 = #ID)
Just include the condition in your SQL as an OR, note the brackets
SELECT * FROM myTable WHERE Column1 = 'test' AND (#ID = -1 OR Column2 = #ID)
One alternative:
SELECT * FROM myTable WHERE Column1 = 'test' AND #ID in (-1,Column2)
Related
I have a stored procedure with one parameter, #ID, which is an integer that might be zero. When it is zero, I want to use it as if it is null. So here is how I have written my query:
If #ID = 0
SELECT * FROM MyTable WHERE ID IS NULL
ELSE
SELECT * FROM MyTable WHERE ID = #ID;
This is quite inelegant. Surely there is a way to write the WHERE clause in such a way that makes duplicating the SELECT statement unnecessary.
You can phrase this more simply using:
SELECT *
FROM MyTable
WHERE COALESCE(ID, 0) = #id;
Next, you probably do not want to do this. It will prevent SQL Server from using an index. Similarly, OR is likely to prevent optimization as well.
Probably your best bet is your current code, or UNION ALL:
SELECT *
FROM MyTable
WHERE ID IS NULL AND #id = 0
UNION ALL
SELECT *
FROM MyTable
WHERE ID = #ID; -- not sure if `#id <> 0` is needed here
With this or your approach, you probably need OPTION (RECOMPILE) to ensure that an index is always used.
Just combine them using AND/OR logic:
SELECT *
FROM MyTable
WHERE (#Id != 0 AND ID = #ID)
OR (#Id = 0 AND ID IS NULL);
Before you shout at me in CAPS for not searching - I have! Dynamic SQL is good, dynamic SQL is bad. Learning a lot..
I can accomplish what I'm after by using logic in there WHERE clause, but it adds a significant amount of run time. The query takes 8 seconds if I hard code the criteria and 1:20 if I use the WHERE logic.
Here is what I'd like to do:
Declare #EmployeeToggle varchar(30)
Declare #Employee_ID varchar(30)
Declare #EmployeeField varchar(100)
set #EmployeeToggle = '1'
set #Employee_ID = '1166'
set #EmployeeField = case when #EmployeeToggle = '1' then 'Field1' else
'Field2' end;
select * from Table1 where #EmployeeField = #Employee_ID
I don't think it's possible without dynamic sql. I still don't know whether or not I should use it. It's my thought that it would take the query back down to 8 seconds, because it would immediately know which field to use in the where clause.
Alternatively, a few ways to do it in the where only:
where (( not #EmployeeToggle = '1') or Field1 = #Employee_ID) and
(#EmployeeToggle = '1' or Field2 = #Employee_ID)
where (1=(case when #EmployeeToggle = '1' then 1 else 0 end ) or Field1 =
#Employee_ID)
and (1=(case when #EmployeeToggle = '2' then 1 else 0 end) or Field2 =
#Employee_ID)
These work great (admittedly I copied and pasted these examples), but at the expense of run time.
My final thought, and the way others have done it at my org, is to create two scripts that are identical except for the field used in the where clause. So, if #EmployeeToggle = '1' it will run the first script and if it's '2' it will run the second. I haven't tried that yet, but I assume the runtime will be closer to the 8 seconds at the expense of some ugly code.
Thanks for the help.
Why not just use a single query?
select t.*
from table1
where #EmployeeToggle = '1' and field_1 = #Employee_ID
union all
select t.*
from table1
where #EmployeeToggle <> '1' and field_2 = #Employee_ID;
By using union all, SQL Server should use indexes for each subquery -- and if you have indexes on the fields, the query should be fast.
You can stay with static SQL when using CASE expression in SELECT then filter it.
SELECT *
FROM (
SELECT *,
CASE WHEN #EmployeeToggle = '1' THEN Field1 ELSE Field2 END AS Field1_2
FROM Table1
) t
WHERE
Field1_2 = #Employee_ID
Here is your dynamic query:
Declare #EmployeeToggle varchar(30)
Declare #Employee_ID varchar(30)
Declare #EmployeeField varchar(100)
set #EmployeeToggle = '1'
set #Employee_ID = '1166'
set #EmployeeField = case when #EmployeeToggle = '1' then 'Field1' else
'Field2' end;
DECLARE #SQLString VARCHAR(MAX)
SET #SQLString='select *
from Table1
where '+#EmployeeField+' = '+#Employee_ID+''
PRINT(#SQLString) --If you want to check actual query
EXEC(#SQLString)
Declare #temp As Int
set #temp = 10
select Column1 from MyTable where Column2 = #temp
select Column1 from MyTable where #temp = Column2
Is there any change in performance based on position of parameter in where clause.
There should be no change. However, You can confirm this by running the execution plan in sql viewer.
No, those two should be identical.
I need to get the output of a selected query depending on certain conditions
Means if(id=uid)
then I need the below query
select * from table1 where id=5;
else
I need the below one
select * from table1 where id=10
I know i can use if condition for this. But my query is very long one so when I use if else then it would look like
if(#id=#uid)
begin
select * from table1 where id=5;// query 1
end
else
select * from table1 where id=10;//query 2
but here I need to replace the entire query once again for a single check. I hope I can do something like this:
declare #id int=4;
declare #uid=10;
select * from table1 where
case
when #id=#uid
then
id=5
else
id=10;
end
Updation
I need one more condition too
in this case id=5 and uid=10
then if(id=uid)
then
select * from table1 where id=5
and
if(id!=uid)
then
select * from table1
something like this
You can use the case expression to return the value id should be equal to:
SELECT *
FROM table1
WHERE id = CASE WHEN #id = #uid THEN 5 ELSE 10 END;
EDIT:
The updated requirement in the question is to return all rows when #id != #uid. This can be done by comparing id to id:
SELECT *
FROM table1
WHERE id = CASE WHEN #id = #uid THEN 5 ELSE id END;
Alternatively, with this updated requirement, a simple or expression might be simpler to use:
SELECT *
FROM table1
WHERE #id = #uid OR id = 5;
SELECT * FROM table1
WHERE (id=5 AND #id=#uid) OR (id=10 AND #id<>#uid)
SELECT
*
FROM
table1
WHERE
(
#id = #uid
AND
id =5
)
OR
(
not #id = #uid
AND
id=10
)
I'm trying to return different data depending on a variable in a SELECT. Something like this:
SELECT
IF #variable = 'YES'
column1, column2
ELSE
column3
FROM TABLE
What is this the proper way to use the IF condition in SQL? Or is there a better alternative to what I'm trying to accomplish?
If you want to return a different number of columns, you'll need to use an IF:
IF #variable = 'YES'
BEGIN
SELECT column1, column2
FROM YourTable
END
ELSE
BEGIN
SELECT column3
FROM YourTable
END
If you want different data on the same column (assuming the same datatype), you could use a CASE:
SELECT CASE WHEN #variable = 'YES' THEN column1 ELSE Column2 AS Data
FROM YourTable
You can use an IF statement, but you'll need to set up multiple queries. You can use a CASE for selecting one column or another, but not to select one or multiple like in your question.
DECLARE #var INT = 1;
DECLARE #test TABLE (
Col1 int,
Col2 int,
Col3 int
)
INSERT INTO #test VALUES (1,2,3)
IF #var = 1
BEGIN
SELECT Col1, Col2
FROM #test
END
ELSE
BEGIN
SELECT Col3
FROM #test
END