I've declared a variable in a stored procedure:
DECLARE #CurrentChunk NVARCHAR(250)
I would like to use the length of the variable, i.e. 250, later in my sp for computational purposes, and I want to keep my code as dry as possible.
Here's my code (assume #Narrative is a param to the SP):
DECLARE #ChunkSizeCharacters INT,
#NumChunks INT,
#LoopIndex INT,
#CurrentChunk NVARCHAR(250)
SET #ChunkSizeCharacters = 250 -- HERE'S WHERE I WANT THE LENGTH OF #CurrentChunk
SET #NumChunks = CEILING((LEN(#Narrative) * 1.0)/#ChunkSizeCharacters)
SET #LoopIndex = 0;
WHILE (#LoopIndex < #NumChunks)
BEGIN
SET #CurrentChunk = SUBSTRING(#Narrative,
((#LoopIndex * #ChunkSizeCharacters) + 1), #ChunkSizeCharacters)
INSERT INTO [dbo].[Chunks] ([Chunk]) VALUES (#CurrentChunk)
SET #LoopIndex = #LoopIndex + 1
END
Is there a way to ascertain the length of an NVARCHAR or VARCHAR variable definition (please read carefully -- I'm not looking for LEN())?
It seems the MaxLength variant property returns the value you're looking for.
DECLARE #Banana varchar(255) = 'This banana'
SELECT SQL_VARIANT_PROPERTY(#Banana, 'MaxLength')
Returns 255.
If you don't mind overwriting the variable (and if you do, you can assign it to a temp NVARCHAR(MAX)):
SELECT #CurrentChunk = REPLICATE(0, 8000);
SELECT #ChunkSizeCharacters = LEN(#CurrentChunk);
This trick does not and cannot work for NVARCHAR(MAX), but that's presumably no problem, given it's enormous maximum size.
Unfortunately T-SQL has nothing in the way of metadata properties for variables. Even determining the type of an expression is a chore.
Interestingly, the value returned by that SELECT SQL_VARIANT_PROPERTY statement doesn't select into a plain, predefined variable. In the end, I used:
DECLARE #Text VARCHAR(400), #TextLen INT
SELECT #TextLen = CAST(SQL_VARIANT_PROPERTY(ISNULL(#Text, ''), 'MaxLength') AS INT)
Works like a charm for me!
The following code is resulting in an infinite loop or really really slow execution:
CREATE FUNCTION [dbo].[CleanUriPart]
(
-- Add the parameters for the function here
#DirtyUriPart nvarchar(200)
)
RETURNS nvarchar(200)
AS
BEGIN;
-- Declare the return variable here
DECLARE #Result nvarchar(200);
DECLARE #i int;
SET #i = 1;
WHILE 1 = 1
BEGIN;
SET #i = PATINDEX('%[^a-zA-Z0-9.~_-]%', #DirtyUriPart COLLATE Latin1_General_BIN);
IF #i > 0
SET #DirtyUriPart = STUFF(#DirtyUriPart, #i, 1, '-');
ELSE
BREAK;
END;
-- Add the T-SQL statements to compute the return value here
SELECT #Result = #DirtyUriPart;
-- Return the result of the function
RETURN #Result;
END;
The input/output should be as follows:
'abcdef' -> 'abcdef' works ok
'abc-def' -> 'abc-def' results in infinite loop
'abc*def' -> 'abc-def' results in infinite loop
etc.
Please help!
SELECT PATINDEX('%[^a-]%', N'aaa-def' COLLATE Latin1_General_BIN),
PATINDEX('%[^-a]%', N'aaa-def' COLLATE Latin1_General_BIN),
PATINDEX('%[^a-]%', 'aaa-def' COLLATE Latin1_General_BIN),
PATINDEX('%[^-a]%', 'aaa-def' COLLATE Latin1_General_BIN)
Returns
----------- ----------- ----------- -----------
1 5 5 5
So it seems that for varchar datatypes a trailing - is treated as being part of a set whereas for nvarchar it is ignored (treated as a malformed range as a is ignored too?)
The BOL entry for LIKE doesn't explicitly talk about how to use - within [] to get it to be treated as part of a set but does have the example
LIKE '[-acdf]'
to match -, a, c, d, or f so I assume that it needs to be the first item in a set (i.e. that [^a-zA-Z0-9.~_-] needs to be altered to [^-a-zA-Z0-9.~_]). That also matches the result of my testing above.
Any chance #DirtyUriPart can evaluate to NULL? ON the PATINDEX function, if either pattern or expression is NULL, PATINDEX returns NULL and a NULL in this case will cause a infinite loop
It looks like you could fix the problem by casting #DirtyUriPart as VARCHAR(200) in PATINDEX, which will cause the dash to be recognized along with the other characters in the class:
DECLARE #DirtyUriPart nvarchar(200)='abc-def';
-- Returns 0
SELECT PATINDEX('%[^a-zA-Z0-9.~_-]%', CAST(#DirtyUriPart AS VARCHAR(200)) COLLATE Latin1_General_BIN);
-- Returns 4
SELECT PATINDEX('%[^a-zA-Z0-9.~_-]%', #DirtyUriPart COLLATE Latin1_General_BIN);
How do I check if an argument in a stored procedure is an empty GUID or not?
SELECT CAST(CAST(0 AS BINARY) AS UNIQUEIDENTIFIER)
That should return your empty guid.
... or even shorter, saving one cast:
SELECT CAST(0x0 AS UNIQUEIDENTIFIER)
So to check for that, you would do
IF #GuidParam = CAST(CAST(0 AS BINARY) AS UNIQUEIDENTIFIER)
BEGIN
--Guid is empty
END
Since the empty guid never changes, the other obvious way is to simply use 00000000-0000-0000-0000-000000000000 rather than calculating it.
If #Param = '00000000-0000-0000-0000-000000000000'
...
Or, if in an procedure, you can set a parameter to act as a constant:
Declare #EmptyGuid uniqueidentifier
Set #EmptyGuid = '00000000-0000-0000-0000-000000000000'
Or you could create a scalar user-defined function which simply returns the above constant value (or recalculates it as in Meiscooldude solution).
DECLARE #EmptyGuid UNIQUEIDENTIFIER = 0x0
DECLARE #NonEmpty UNIQUEIDENTIFIER = NEWID()
IF #EmptyGuid = 0x0 PRINT 'Empty'
IF #NonEmpty = 0x0 PRINT 'Empty' ELSE PRINT 'NonEmpty'
Will print
Empty
NonEmpty
You can make Empty Guid like this:
DECLARE #EmptyGuid UNIQUEIDENTIFIER
SET #EmptyGuid = (SELECT CAST(CAST(0 AS BINARY) AS UNIQUEIDENTIFIER))
-- Single result is 00000000-0000-0000-0000-000000000000
SELECT #EmptyGuid
Use
DECLARE #param UNIQUEIDENTIFIER = NEWID();
--DECLARE #param UNIQUEIDENTIFIER = '00000000-0000-0000-0000-000000000000'
IF (CONVERT(UNIQUEIDENTIFIER, 0x00)) = #param
PRINT 'Empty';
ELSE
PRINT 'Not Empty';
DECLARE #SupplierDataHubId uniqueidentifier=null
set #SupplierDataHubId=(select HubId from dbo.tblSupplierData where fldUpc='603259049389' OR fldEan='6032590493895555')
if (#SupplierDataHubId is not null)
begin
print('yes');
end
else
print 'no'
I created the following function to simplify a piece of particularly complex code.
CREATE FUNCTION [dbo].[DSGetMinimumInt] (#First INT, #Second INT)
RETURNS INT
AS
BEGIN
IF #First < #Second
RETURN #First
RETURN #Second
END
However, it only works for the INT datatype. I know I could create one for numeric and possibly for Varchar and Datetime.
Is it possible to create one master "Minimum" function to deal with them all? Has anyone done this?
I've Googled it, but come up empty.
here is a basic one you can work with, I'd be careful using this in queries, as it will slow them down in proportion to the number of rows it is used on:
CREATE FUNCTION [dbo].[DSGetMinimum] (#First sql_variant, #Second sql_variant)
RETURNS varchar(8000)
AS
BEGIN
DECLARE #Value varchar(8000)
IF SQL_VARIANT_PROPERTY(#First,'BaseType')=SQL_VARIANT_PROPERTY(#Second,'BaseType')
OR #First IS NULL OR #Second IS NULL
BEGIN
IF SQL_VARIANT_PROPERTY(#First,'BaseType')='datetime'
BEGIN
IF CONVERT(datetime,#First)<CONVERT(datetime,#Second)
BEGIN
SET #Value=CONVERT(char(23),#First,121)
END
ELSE
BEGIN
SET #Value=CONVERT(char(23),#Second,121)
END
END --IF datetime
ELSE
BEGIN
IF #First < #Second
SET #Value=CONVERT(varchar(8000),#First)
ELSE
SET #Value=CONVERT(varchar(8000),#Second)
END
END --IF types the same
RETURN #Value
END
GO
EDIT
Test Code:
DECLARE #D1 datetime , #D2 datetime
DECLARE #I1 int , #I2 int
DECLARE #V1 varchar(5) , #V2 varchar(5)
SELECT #D1='1/1/2010', #D2='1/2/2010'
,#I1=5 , #I2=999
,#V1='abc' , #V2='xyz'
PRINT dbo.DSGetMinimumInt(#D1,#D2)
PRINT dbo.DSGetMinimumInt(#I1,#I2)
PRINT dbo.DSGetMinimumInt(#V1,#V2)
Test Output:
2010-01-01 00:00:00.000
5
abc
If you are going to use this in a query, I would just use an inline CASE statement, which would be MUCH faster then the UDF:
CASE
WHEN #valueAnyType1<#ValueAnyType2 THEN #valueAnyType1
ELSE #ValueAnyType2
END
you can add protections for NULL if necessary:
CASE
WHEN #valueAnyType1<=ISNULL(#ValueAnyType2,#valueAnyType1) THEN #valueAnyType1
ELSE #ValueAnyType2
END
All major databases except SQL Server support LEAST and GREATEST which do what you want.
In SQL Server, you can emulate it this way:
WITH q (col1, col2) AS
(
SELECT 'test1', 'test2'
UNION ALL
SELECT 'test3', 'test4'
)
SELECT (
SELECT MIN(col)
FROM (
SELECT col1 AS col
UNION ALL
SELECT col2
) qa
)
FROM q
, though it will be a little bit less efficient than a UDF.
Azure SQL DB (and future SQL Server versions) now supports GREATEST/LEAST:
GREATEST
LEAST
Is there a way to make a TSQL variable constant?
No, but you can create a function and hardcode it in there and use that.
Here is an example:
CREATE FUNCTION fnConstant()
RETURNS INT
AS
BEGIN
RETURN 2
END
GO
SELECT dbo.fnConstant()
One solution, offered by Jared Ko is to use pseudo-constants.
As explained in SQL Server: Variables, Parameters or Literals? Or… Constants?:
Pseudo-Constants are not variables or parameters. Instead, they're simply views with one row, and enough columns to support your constants. With these simple rules, the SQL Engine completely ignores the value of the view but still builds an execution plan based on its value. The execution plan doesn't even show a join to the view!
Create like this:
CREATE SCHEMA ShipMethod
GO
-- Each view can only have one row.
-- Create one column for each desired constant.
-- Each column is restricted to a single value.
CREATE VIEW ShipMethod.ShipMethodID AS
SELECT CAST(1 AS INT) AS [XRQ - TRUCK GROUND]
,CAST(2 AS INT) AS [ZY - EXPRESS]
,CAST(3 AS INT) AS [OVERSEAS - DELUXE]
,CAST(4 AS INT) AS [OVERNIGHT J-FAST]
,CAST(5 AS INT) AS [CARGO TRANSPORT 5]
Then use like this:
SELECT h.*
FROM Sales.SalesOrderHeader h
JOIN ShipMethod.ShipMethodID const
ON h.ShipMethodID = const.[OVERNIGHT J-FAST]
Or like this:
SELECT h.*
FROM Sales.SalesOrderHeader h
WHERE h.ShipMethodID = (SELECT TOP 1 [OVERNIGHT J-FAST] FROM ShipMethod.ShipMethodID)
My workaround to missing constans is to give hints about the value to the optimizer.
DECLARE #Constant INT = 123;
SELECT *
FROM [some_relation]
WHERE [some_attribute] = #Constant
OPTION( OPTIMIZE FOR (#Constant = 123))
This tells the query compiler to treat the variable as if it was a constant when creating the execution plan. The down side is that you have to define the value twice.
No, but good old naming conventions should be used.
declare #MY_VALUE as int
There is no built-in support for constants in T-SQL. You could use SQLMenace's approach to simulate it (though you can never be sure whether someone else has overwritten the function to return something else…), or possibly write a table containing constants, as suggested over here. Perhaps write a trigger that rolls back any changes to the ConstantValue column?
Prior to using a SQL function run the following script to see the differences in performance:
IF OBJECT_ID('fnFalse') IS NOT NULL
DROP FUNCTION fnFalse
GO
IF OBJECT_ID('fnTrue') IS NOT NULL
DROP FUNCTION fnTrue
GO
CREATE FUNCTION fnTrue() RETURNS INT WITH SCHEMABINDING
AS
BEGIN
RETURN 1
END
GO
CREATE FUNCTION fnFalse() RETURNS INT WITH SCHEMABINDING
AS
BEGIN
RETURN ~ dbo.fnTrue()
END
GO
DECLARE #TimeStart DATETIME = GETDATE()
DECLARE #Count INT = 100000
WHILE #Count > 0 BEGIN
SET #Count -= 1
DECLARE #Value BIT
SELECT #Value = dbo.fnTrue()
IF #Value = 1
SELECT #Value = dbo.fnFalse()
END
DECLARE #TimeEnd DATETIME = GETDATE()
PRINT CAST(DATEDIFF(ms, #TimeStart, #TimeEnd) AS VARCHAR) + ' elapsed, using function'
GO
DECLARE #TimeStart DATETIME = GETDATE()
DECLARE #Count INT = 100000
DECLARE #FALSE AS BIT = 0
DECLARE #TRUE AS BIT = ~ #FALSE
WHILE #Count > 0 BEGIN
SET #Count -= 1
DECLARE #Value BIT
SELECT #Value = #TRUE
IF #Value = 1
SELECT #Value = #FALSE
END
DECLARE #TimeEnd DATETIME = GETDATE()
PRINT CAST(DATEDIFF(ms, #TimeStart, #TimeEnd) AS VARCHAR) + ' elapsed, using local variable'
GO
DECLARE #TimeStart DATETIME = GETDATE()
DECLARE #Count INT = 100000
WHILE #Count > 0 BEGIN
SET #Count -= 1
DECLARE #Value BIT
SELECT #Value = 1
IF #Value = 1
SELECT #Value = 0
END
DECLARE #TimeEnd DATETIME = GETDATE()
PRINT CAST(DATEDIFF(ms, #TimeStart, #TimeEnd) AS VARCHAR) + ' elapsed, using hard coded values'
GO
If you are interested in getting optimal execution plan for a value in the variable you can use a dynamic sql code. It makes the variable constant.
DECLARE #var varchar(100) = 'some text'
DECLARE #sql varchar(MAX)
SET #sql = 'SELECT * FROM table WHERE col = '''+#var+''''
EXEC (#sql)
For enums or simple constants, a view with a single row has great performance and compile time checking / dependency tracking ( cause its a column name )
See Jared Ko's blog post https://blogs.msdn.microsoft.com/sql_server_appendix_z/2013/09/16/sql-server-variables-parameters-or-literals-or-constants/
create the view
CREATE VIEW ShipMethods AS
SELECT CAST(1 AS INT) AS [XRQ - TRUCK GROUND]
,CAST(2 AS INT) AS [ZY - EXPRESS]
,CAST(3 AS INT) AS [OVERSEAS - DELUXE]
, CAST(4 AS INT) AS [OVERNIGHT J-FAST]
,CAST(5 AS INT) AS [CARGO TRANSPORT 5]
use the view
SELECT h.*
FROM Sales.SalesOrderHeader
WHERE ShipMethodID = ( select [OVERNIGHT J-FAST] from ShipMethods )
Okay, lets see
Constants are immutable values which are known at compile time and do not change for the life of the program
that means you can never have a constant in SQL Server
declare #myvalue as int
set #myvalue = 5
set #myvalue = 10--oops we just changed it
the value just changed
Since there is no build in support for constants, my solution is very simple.
Since this is not supported:
Declare Constant #supplement int = 240
SELECT price + #supplement
FROM what_does_it_cost
I would simply convert it to
SELECT price + 240/*CONSTANT:supplement*/
FROM what_does_it_cost
Obviously, this relies on the whole thing (the value without trailing space and the comment) to be unique. Changing it is possible with a global search and replace.
There are no such thing as "creating a constant" in database literature. Constants exist as they are and often called values. One can declare a variable and assign a value (constant) to it. From a scholastic view:
DECLARE #two INT
SET #two = 2
Here #two is a variable and 2 is a value/constant.
SQLServer 2022 (currently only as Preview available) is now able to Inline the function proposed by SQLMenace, this should prevent the performance hit described by some comments.
CREATE FUNCTION fnConstant() RETURNS INT AS BEGIN RETURN 2 END GO
SELECT is_inlineable FROM sys.sql_modules WHERE [object_id]=OBJECT_ID('dbo.fnConstant');
is_inlineable
1
SELECT dbo.fnConstant()
ExecutionPlan
To test if it also uses the value coming from the Function, I added a second function returning value "1"
CREATE FUNCTION fnConstant1()
RETURNS INT
AS
BEGIN
RETURN 1
END
GO
Create Temp Table with about 500k rows with Value 1 and 4 rows with Value 2:
DROP TABLE IF EXISTS #temp ;
create table #temp (value_int INT)
DECLARE #counter INT;
SET #counter = 0
WHILE #counter <= 500000
BEGIN
INSERT INTO #temp VALUES (1);
SET #counter = #counter +1
END
SET #counter = 0
WHILE #counter <= 3
BEGIN
INSERT INTO #temp VALUES (2);
SET #counter = #counter +1
END
create index i_temp on #temp (value_int);
Using the describe plan we can see that the Optimizer expects 500k values for
select * from #temp where value_int = dbo.fnConstant1(); --Returns 500001 rows
Constant 1
and 4 rows for
select * from #temp where value_int = dbo.fnConstant(); --Returns 4rows
Constant 2
Robert's performance test is interesting. And even in late 2022, the scalar functions are much slower (by an order of magnitude) than variables or literals. A view (as suggested mbobka) is somewhere in-between when used for this same test.
That said, using a loop like that in SQL Server is not something I'd ever do, because I'd normally be operating on a whole set.
In SQL 2019, if you use schema-bound functions in a set operation, the difference is much less noticeable.
I created and populated a test table:
create table #testTable (id int identity(1, 1) primary key, value tinyint);
And changed the test so that instead of looping and changing a variable, it queries the test table and returns true or false depending on the value in the test table, e.g.:
insert #testTable(value)
select case when value > 127
then #FALSE
else #TRUE
end
from #testTable with(nolock)
I tested 5 scenarios:
hard-coded values
local variables
scalar functions
a view
a table-valued function
running the test 10 times, yielded the following results:
scenario
min
max
avg
scalar functions
233
259
240
hard-coded values
236
265
243
local variables
235
278
245
table-valued function
243
272
253
view
244
267
254
Suggesting to me, that for set-based work in (at least) 2019 and better, there's not much in it.
set nocount on;
go
-- create test data table
drop table if exists #testTable;
create table #testTable (id int identity(1, 1) primary key, value tinyint);
-- populate test data
insert #testTable (value)
select top (1000000) convert(binary (1), newid())
from sys.all_objects a
, sys.all_objects b
go
-- scalar function for True
drop function if exists fnTrue;
go
create function dbo.fnTrue() returns bit with schemabinding as
begin
return 1
end
go
-- scalar function for False
drop function if exists fnFalse;
go
create function dbo.fnFalse () returns bit with schemabinding as
begin
return 0
end
go
-- table-valued function for booleans
drop function if exists dbo.tvfBoolean;
go
create function tvfBoolean() returns table with schemabinding as
return
select convert(bit, 1) as true, convert(bit, 0) as false
go
-- view for booleans
drop view if exists dbo.viewBoolean;
go
create view dbo.viewBoolean with schemabinding as
select convert(bit, 1) as true, convert(bit, 0) as false
go
-- create table for results
drop table if exists #testResults
create table #testResults (id int identity(1,1), test int, elapsed bigint, message varchar(1000));
-- define tests
declare #tests table(testNumber int, description nvarchar(100), sql nvarchar(max))
insert #tests values
(1, N'hard-coded values', N'
declare #testTable table (id int, value bit);
insert #testTable(id, value)
select id, case when t.value > 127
then 0
else 1
end
from #testTable t')
, (2, N'local variables', N'
declare #FALSE as bit = 0
declare #TRUE as bit = 1
declare #testTable table (id int, value bit);
insert #testTable(id, value)
select id, case when t.value > 127
then #FALSE
else #TRUE
end
from #testTable t'),
(3, N'scalar functions', N'
declare #testTable table (id int, value bit);
insert #testTable(id, value)
select id, case when t.value > 127
then dbo.fnFalse()
else dbo.fnTrue()
end
from #testTable t'),
(4, N'view', N'
declare #testTable table (id int, value bit);
insert #testTable(id, value)
select id, case when value > 127
then b.false
else b.true
end
from #testTable t with(nolock), viewBoolean b'),
(5, N'table-valued function', N'
declare #testTable table (id int, value bit);
insert #testTable(id, value)
select id, case when value > 127
then b.false
else b.true
end
from #testTable with(nolock), dbo.tvfBoolean() b')
;
declare #testNumber int, #description varchar(100), #sql nvarchar(max)
declare #testRuns int = 10;
-- execute tests
while #testRuns > 0 begin
set #testRuns -= 1
declare testCursor cursor for select testNumber, description, sql from #tests;
open testCursor
fetch next from testCursor into #testNumber, #description, #sql
while ##FETCH_STATUS = 0 begin
declare #TimeStart datetime2(7) = sysdatetime();
execute sp_executesql #sql;
declare #TimeEnd datetime2(7) = sysdatetime()
insert #testResults(test, elapsed, message)
select #testNumber, datediff_big(ms, #TimeStart, #TimeEnd), #description
fetch next from testCursor into #testNumber, #description, #sql
end
close testCursor
deallocate testCursor
end
-- display results
select test, message, count(*) runs, min(elapsed) as min, max(elapsed) as max, avg(elapsed) as avg
from #testResults
group by test, message
order by avg(elapsed);
The best answer is from SQLMenace according to the requirement if that is to create a temporary constant for use within scripts, i.e. across multiple GO statements/batches.
Just create the procedure in the tempdb then you have no impact on the target database.
One practical example of this is a database create script which writes a control value at the end of the script containing the logical schema version. At the top of the file are some comments with change history etc... But in practice most developers will forget to scroll down and update the schema version at the bottom of the file.
Using the above code allows a visible schema version constant to be defined at the top before the database script (copied from the generate scripts feature of SSMS) creates the database but used at the end. This is right in the face of the developer next to the change history and other comments, so they are very likely to update it.
For example:
use tempdb
go
create function dbo.MySchemaVersion()
returns int
as
begin
return 123
end
go
use master
go
-- Big long database create script with multiple batches...
print 'Creating database schema version ' + CAST(tempdb.dbo.MySchemaVersion() as NVARCHAR) + '...'
go
-- ...
go
-- ...
go
use MyDatabase
go
-- Update schema version with constant at end (not normally possible as GO puts
-- local #variables out of scope)
insert MyConfigTable values ('SchemaVersion', tempdb.dbo.MySchemaVersion())
go
-- Clean-up
use tempdb
drop function MySchemaVersion
go