I am creating a stored proc that selects a value from a table and uses it in another procedure. If the first value that is searched doesn’t exist I need it to use a default value. I’m new to stored procs so I’m not sure of the best practices.
Here is the first select statement which may or may not return a value. If it doesn’t return a value I need to set the “#theValue” to 10 so that it can be used in the next select statement.
DECLARE #TheValue nvarchar(50)
SELECT #TheValue = deviceManager.SystemSettings.Value
FROM deviceManager.SystemSettings
WHERE (deviceManager.SystemSettings.Setting = 'expire-terminal-requests'
What would be the best solution?
DECLARE #TheValue nvarchar(50)
SELECT #TheValue = deviceManager.SystemSettings.Value
FROM deviceManager.SystemSettings
WHERE (deviceManager.SystemSettings.Setting = 'expire-terminal-requests'
-- Assuming #TheValue is an output parameter
SELECT #TheValue = ISNULL(#TheValue, 10)
Another possibility, set the default value before the query
DECLARE #TheValue nvarchar(50)
SET #TheValue = 'Some default Value'
SELECT #TheValue = deviceManager.SystemSettings.Value
FROM deviceManager.SystemSettings
WHERE deviceManager.SystemSettings.Setting = 'expire-terminal-requests'
This will always return either the default or the correct value.
Hope this helps.
#TheValue will be NULL if the select doesn't hit any rows. And NULL is a good value to indicate "not found".
One trick with NULLs is that you have to check for them with is null instead of = null, for example:
where #TheValue is NULL
coalesce returns the first non-null value from the list, is also ANSI standard.
SET #TheValue = coalesce (some_expresson_that_may_return_null
,some_other_expresson_that_may_return_null
,and_another_expresson_that_may_return_null
,default_value)
Related
The code snippet below is what I'm trying to achieve, but I'm having trouble making it work. If the parameter that gets passed into the procedure is null, I want to only return the rows with a WHERE clause IS NULL, but if there is a value, I want to return the rows that are equal to the value passed in. Dynamic SQL seems like it would work, but I'm curious if there's an easier way I'm missing. Thanks in advance.
PARAM:
#id varchar(10) = '123456789'
SELECT *
FROM TABLE T
WHERE
CASE
WHEN #id IS NULL THEN (id IS NULL)
ELSE id = #id
END
The logic you want is:
WHERE (#id IS NULL AND id IS NULL) OR
id = #id
You're trying to use a CASE expression like a Case (Switch) statement. Switches don't exist in T-SQL, and a CASE expression returns a scalar value not a boolean result.
Don't, however, use CASE expressions in the WHERE, use proper Boolean logic:
SELECT *
FROM YourTable YT
WHERE (ID = #ID
OR (ID IS NULL AND #ID IS NULL))
I have written a stored procedure that hashes the value of a certain column. I need to use this HASHBYTES function in a CASE WHEN or IIF statement, like this:
DECLARE #Hash varchar(255) = 'testvalue'
SELECT IIF(1=1, HASHBYTES('SHA1',#Hash), #Hash)
SELECT CASE WHEN 1=1 THEN HASHBYTES('SHA1',#Hash) END AS Hashcolumn
I can't get my head around why I get different outputs from above queries? it seems that whenever I add an ELSE in the CASE WHEN / IIF statement, it returns a string of weird characters (like ü<þ+OUL'RDOk{\Ìø in above example).
Can anyone tell me why this is happening? I need to use the CASE WHEN or IIF.
Thanks guys
IIF returns the data type with the highest precedence from the types in true_value and false_value. In this case, it's #Hash1 which is varchar(255) so your result is getting cast to varchar(255). See below.
DECLARE #Hash varchar(255) = 'testvalue'
SELECT cast(HASHBYTES('SHA1',#Hash) as varchar(255))
Similarly, CASE works the same way. However, if you don't add an ELSE or another WHEN that would conflict with the data type, it will work. This is because an ELSE NULL is implied. i.e.
SELECT CASE WHEN 1=1 THEN HASHBYTES('SHA1',#Hash) END
However, if you add another check, then precedence kicks in, and it will be converted.
SELECT CASE WHEN 1=1 THEN HASHBYTES('SHA1',#Hash) WHEN 1=2 THEN #Hash END AS Hashcolumn
SELECT CASE WHEN 1=1 THEN HASHBYTES('SHA1',#Hash) ELSE #Hash END AS Hashcolumn
The output of a select query is a virtual table. In a relational db a column of a table is constrained to single data type.. so here what happens is implicit conversion is being done by the server engine inorder to render a sigle type and hence weird characters are returned.
The nature of conversion is as #scsimon says it follows highest precedence order.
The following query should help.
DECLARE #Hash varchar(255) = 'testvalue'
SELECT IIF(1=1, CONVERT(VARCHAR(255),HASHBYTES('SHA1',#Hash),2), #Hash)
SELECT CASE WHEN 1=2 THEN CONVERT(VARCHAR(255),HASHBYTES('SHA1',#Hash),2)
ELSE #Hash END AS Hashcolumn
Quick question on Coalesce:
clw.ClawbackPercent = Coalesce(#ClawbackPercent, clw.ClawbackPercent)
Lets say for column 'ClawbackPercent' I have a value of 100.
If I execute a proc and set parameter #ClawbackPercent to have the value NULL, it keeps the value 100 in the row for that column which is great.
However, if I want to set 100 to actually be NULL, what do I need to write in the exec proc statement or what do I need to add in the Coalesce statement?
Thank you
It sounds like you want 100 to be the Default value of a stored proc parameter, not necessarily to replace all NULLs with this value. If this is the case, you don't want a COALESCE but you do need to provide a default value for the parameter on the proc definition.
e.g.
CREATE PROC dbo.MyProc (
#MyParam INT = 100
)
AS
-- My code here
If somebody executes this proc without specifying a value for #MyParam, the default of 100 will be assigned. If they explicitly specify #MyParam = NULL then NULL will be assigned..
Then probably you should not use coalesce, instead you can use case statement as below:
clw.ClawbackPercent = CASE WHEN #ClawbackPercent = 100
THEN NULL
ELSE
#ClawbackPercent END
in the select statement
You have to write in the following way:
CREATE PROCEDURE sp_test(
#ClawbackPercent VARCHAR(30)
) AS
BEGIN
SELECT COALESCE(#ClawbackPercent, '100')
END
--call as below and if you want to return second value then, EXEC sp_test NULL
--if your second, thirds... parameters are in INTEGER then simply CAST to VARCHAR
EXEC sp_test 'NULL'
I have SQL script and it needs to check values between two columns to see if the values are different. Earlier I had a simple check using <> but it doesn't seem to cut it when it comes to nulls.
Is the below the only way to check if the values are different?
declare #intValue int = 1;
declare #intNull int = 1;
select 'Values are not the same'
where (#intNull <> #intValue) or (#intValue is null and #intNull is not null) or (#intValue is not null and #intNull is null);
What you have done is correct and, to the best of my knowledge, the only way.
You can done with isnull also.
declare #intValue int = 1;
declare #intNull int = 1;
select 'Values are not the same'
where (isnull(#intNull,'') <> isnull(#intValue,''))
You can pick a dummy value that you know is never used in the data:
coalesce(c1, -9999) <> coalesce(c2, -9999)
It's essentially the same as yours though a little shorter. And it might not be appropriate for all cases.
The title of your question asks for the "best" way. I was responding to the "is this the only way" question later in the body. This will save you some typing but it probably isn't wise to rely on special values like this without serious consideration.
use BINARY_CHECKSUM:
declare #intValue int = 1;
declare #intNull int = NULL;
SELECT CAST(BINARY_CHECKSUM(#intValue) AS BIGINT)
, CAST(BINARY_CHECKSUM(#intNull) AS BIGINT)
BINARY_CHECKSUM works on strings as well.
Why #OpeningDate is getting saved as NULL even though I am doing this.
PROCEDURE [dbo].[InsertCaseANDHearingDetails]
#HearingDate datetime,
#IsOpeningDate bit= null,
#OpeningDate date= null,
AS
Begin
IF(#IsOpeningDate = 0)
Begin
Set #OpeningDate= (Select Convert(varchar, #HearingDate, 106))
End
Insert Into Hearings
values (#HearingDate, #OpeningDate)
End
Even though I am calculating it and hearing date is not null but why OpeningDate is getting saved as NULL.
#HearingDate != NULL will not work. The result of this comparison is always unknown. Use #HearingDate is not null instead.
Because the variable #HearingDate is not initialized, it would have a null value.
Also, the variable #OpeningDate wouldn't be set to Select Convert(varchar, #HearingDate, 106) because the if condition evaluates to unknown.
Hence, when you select values from the table they would be null.
Edit:
#IsOpeningDate bit= null
...
IF(#IsOpeningDate = 0)
This condition evaluates to unknown too as this is doing 0 = null. You cannot compare with null.
It will work if you use the following at the start of the Proc.
SET ANSI_NULLS OFF
Basically NULL can't be compared, not even with itself, because this is not a value. If at all, you want the engine to treat it as one, you need to set off the ANSI_NULLS property. That said, I would prefer to go with #vkp's answer any day.
Based on your edit, it looks like the below condition is not met:
IF(#IsOpeningDate = 0)
and hence, it remains NULL.
in the if condition why dont you check is null instead of comparing it to 0
Your query
IF(#IsOpeningDate = 0)
My suggestion
IF(#IsOpeningDate IS NULL)
Sorry it was my mistake to no mention parameters in Insert statement and since NULL were allowed so it inserted NULLs
Thanks for your help as it led me to figure out that what's actually going on.