Alright so a quick SQL question here(using sql-server-2008).
I have a mapping table names with the following columns
ID DisplayName
What I want to do is first
SELECT [ID] FROM [names] WHERE [DisplayName] = 'chuck';
BUT, if the name 'chuck' doesn't exist in the database, I would like to create it, and return the auto incremented ID.
I was wondering if SQL had some built in way of doing this in an easy way, or if I have to go the long route?
long route being something like this
SELECT COUNT(ID) AS count, ID FROM names WHERE DisplayName='chuck'
IF(count > 0)
SELECT ID as ReturnID;
ELSE
BEGIN
INSERT INTO names(DisplayName) values('chuck');
SELECT scope_identity() as ReturnID;
END
I didn't test that last statement, but I assume the long way would be something like that. If there is no built in way, I'd appreciate it if someone could simply correct that statement(as I'm sure it isn't completely correct).
You should take care about transactions as well:
set XACT_ABORT on
begin tran
declare #ID int
select #ID = ID from names with (holdlock, updlock) WHERE DisplayName='chuck'
if ##rowcount = 0
begin
INSERT INTO names(DisplayName) values('chuck');
set #ID = scope_identity();
end
select #ID as ReturnID;
commit tran
Note the usage of table hints - holdlock and updlock. They prevent another thread from executing exactly the same query and creating the row a second time. For more information look for isolation, synchronization, deadlocks, concurrent updates.
I would do:
IF (NOT EXISTS(SELECT null from names where DisplayName='Chuck'))
INSERT INTO Names (DisplayName) Values ('Chuck')
SELECT ID as ReturnID FROM Names where DisplayName='Chuck'
Doesn't save much though
go
create table names
(
Id int primary key identity(1,1),
displayname varchar(100),
);
go
create procedure P1
#displayname varchar(100)
as
insert into names (displayname)
select #displayname
where not exists (
select * from names, (select #displayname as displayname) as names2
where names.displayname = names2.displayname);
-- race condition is possible here,
-- but in some cases you still may get away with this
select id from names where displayname = #displayname;
go
declare #dn varchar(100);
set #dn = 'chuck'; exec P1 #dn; exec P1 #dn; exec P1 #dn;
set #dn = 'buck'; exec P1 #dn; exec P1 #dn;
select * from names;
go
drop table names; drop procedure P1;
Output would 1, 1, 1, 2, 2 and the table content two rows big.
Related
I have one table which consists of one trigger which will be called if any insert or update operation performed on that table.
This trigger will insert a new row in other physical table.
First I am taking the entire data to be inserted into a temporary table and then I am inserting data into my physical table(which has trigger).
After performing insert operation all the records in the temporary table are getting inserted into physical table but the trigger is executing for only first record, for rest of the records it is not executing.
Can anyone please help me with this issue.
NOTE : With cursor it is working fine but for performance issue I don't want to use cursor.
ALTER TRIGGER [dbo].[MY_TRG]
ON [dbo].[T_EMP_DETAILS]
FOR INSERT , UPDATE
AS
BEGIN
IF UPDATE(S_EMPLOYEE_ID)OR UPDATE(S_GRADE_ID)OR UPDATE(D_EFFECTIVE_DATE) OR UPDATE(S_EMPLOYEE_STATUS)
BEGIN
DECLARE #EmpId varchar(6)
DECLARE #HeaderId Int
DECLARE #FYStartYear varchar(4)
DECLARE #EffDate Smalldatetime
DECLARE #UpdatedBy varchar(10)
DECLARE #ActionType varchar(1)
DECLARE #RowCount Int
DECLARE #EmpRowCount Int
DECLARE #AuditRowsCount Int
DECLARE #EMP_STATUS VARCHAR(1)
DECLARE #D_FIN_START_YEAR DATETIME
DECLARE #Food_Count int
SELECT #FYStartYear = CAST(YEAR(D_CURRENT_FY_ST_DATE)AS VARCHAR) FROM dbo.APPLICATION WHERE B_IS_CURRENT_FY = 1
SELECT #UpdatedBy = 'SHARDUL'
select #EmpId = S_EMPLOYEE_ID from inserted
select #HeaderId = N_HEADER_TXN_ID from inserted
select #EffDate = D_EFFECTIVE_DATE from inserted
select #FLEXI_AMT = N_FLEX_BASKET_AMT from inserted
select #EMP_STATUS = S_EMPLOYEE_STATUS from inserted
select #D_FIN_START_YEAR=D_FIN_START_DATE from inserted
SELECT #RowCount = count(*) from T_EMP_DETAILS
WHERE S_EMPLOYEE_ID = #EmpId and
SUBSTRING(CAST(D_EFFECTIVE_DATE AS VARCHAR),1,11) = SUBSTRING(CAST(#EffDate AS VARCHAR),1,11)
BEGIN
exec INSERT_DEFAULT_VALUES #EmpId,#HeaderId,#UpdatedBy
END
That's one of many reasons Bulk is so fast :). Read Bulk Insert syntax and you'll see FIRE_TRIGGERS parameter. Use it.
As I wrote in my comment - you are using inserted in improper way. As written now it will work only for 1 row.
The second one is a WEIRD number of variables, and only few are used, why?
Third - you are using SP in the end of batch, you need to post it's code, I bet there is some insert in it, maybe you could avoid using this SP and insert directly in some table from inserted.
Not sure if this is the best approach, but I have a stored procedure with an OUTPUT parameter as follows;
create procedure [dbo].[sp_get_site_idx]
#site_name varchar(100),
#result uniqueidentifier output
as
begin
select #result = [primary_idx_col] from [site] where upper([site].[site_name]) = upper(#site_name);
if (#result is null)
begin
< insert a new row>
< run the above select statement again>
end;
end;
When a #site_name that I know does not exist is supplied, the condition (#result is null) is never true, in fact #result appears to be undefined (similar to when there's an exception in a programming language).
Table [site] was created as:
create table [site] (
[primary_idx_col] UNIQUEIDENTIFIER DEFAULT NEWID() constraint pk_site_pk primary key,
...
);
Strangely, if I slightly modify the select statement to:
select #result = [primary_idx_col] from [site] where upper([site].[site_name]) = upper(#site_name) group by [primary_idx_col];
then (#result is null) will evaluate to true.
Please could you explain this behaviour? What is worng with the first select statement?
Thanks in advance.
UNIQUEIDENTIFIER can be checked against NULL.
I tried putting your code into a test database, and the logic seems to be working for me.
If I call your Stored Procedure with:
DECLARE #RESULT2 UNIQUEIDENTIFIER;
EXEC dbo.SP_GET_SITE_IDX #SITE_NAME = '<INSERT VALUE HERE>', -- varchar(100)
#RESULT = #RESULT2 OUTPUT;-- uniqueidentifier
SELECT #RESULT2
then I get the proper result depending on whether the site name is in the table or not.
Does it not insert the row in your IF, in the procedure?
Are you sure the site in question is not in your table?
It is possible that the site is in your table, but with a NULL key/value?
I have a stored procedure that returns an unique Id. I need to call this sp to get the unique ID for each row. I must use this SP because an application also uses this.
How can I select for each row a ID that is returned from the SP?
CREATE procedure [dbo].[SelectNextNumber]
#TableName nvarchar(255)
as
begin
declare #NewSeqVal int
set NOCOUNT ON
update Number --This is a table that holds for each table the max ID
set #NewSeqVal = Next = Next + Increase
where TableNaam= #TableName
if ##rowcount = 0
begin
Insert into Number VALUES (#TableName, 1, 1)
return 1
end
return #NewSeqVal
The number table:
CREATE TABLE [dbo].[Number](
[TableName] [varchar](25) NOT NULL,
[Next] [int] NULL,
[Increase] [int] NULL
I have seen that a While loop is usable for this but in my situation I don't know how to use a while loop.
You can't use stored procedures inside a SELECT statement, only functions.
You can iterate on a resultset with a cursor if you really have to use a stored procedure:
http://msdn.microsoft.com/library/ms180169.aspx
EDIT:
To be honest I'm not very sure to have understood what you really need, it looks like you are building a IDENTITY by yourself ( http://msdn.microsoft.com/library/ms174639(v=sql.105).aspx );
still, if you really need to run a cursor here's an example which uses your stored procedure:
http://sqlfiddle.com/#!3/2b81a/1
Taking the singular INSERT INTO.. SELECT apart:
Temporarily store the SELECT results away
declare #rc int, #NewSeqVal int;
SELECT ..
INTO #tmp -- add this
FROM ..
Store the rowcount and get that many numbers
set #rc = ##rowcount;
For which you have to use the code in the SP directly:
update Number --This is a table that holds for each table the max ID
set #NewSeqVal = Next = Next + #rc
where TableNaam= 'sometbl';
Finally, the insert
INSERT ...
SELECT ID = #NewSeqVal + 1 - row_number() over (ORDER BY col1)
, {all the other columns}
FROM #tmp;
ORDER by Col1 is arbitrary, choose something sensible, or make it ORDER BY NEWID() if you don't care.
I have an Stored Procedure that have an argument named Id:
CREATE PROCEDURE [TargetSp](
#Id [bigint]
)
AS
BEGIN
Update [ATable]
SET [AColumn] =
(
Select [ACalculatedValue] From [AnotherTable]
)
Where [ATable].[Member_Id] = #Id
END
So I need to use it for a list of Id's not for one Id like :
Exec [TargetSp]
#Id IN (Select [M].[Id] From [Member] AS [M] Where [M].[Title] = 'Example');
First: How can I Execute it for a list?
Second: Is there any Performance difference between I execute the sp many times or rewrite it in target script?
You could use a table-valued parameter (see http://msdn.microsoft.com/en-us/library/bb510489.aspx). Generally, if you send only one request to the server instead of a list of requests you will see a shorter execution time.
I normally pass in the information like that as XML, then you can use it just like it's a table... selecting, inserting, updating as necessary
DECLARE #IDS NVARCHAR(MAX), #IDOC INT
SET #IDS = N'<ROOT><ID>1</ID><ID>2<ID></ROOT>'
EXEC sp_xml_preparedocument #IDOC OUTPUT, #IDS
SELECT [ID] FROM OPENXML (#IDOC, '/ROOT/ID', 2) WITH ([ID] INT '.') AS XMLDOC
EXEC sp_xml_removedocument #IDOC
Similar to freefaller's example, but using xml type instead and inserting into a table variable #ParsedIds
DECLARE #IdXml XML = N'<root><id value="1"/><id value="2"/></root>'
DECLARE #ParsedIds TABLE (parsedId int not null)
INSERT INTO #ParsedIds (parsedId)
SELECT v.parsedId.value('#value', 'int')
FROM #IdXml.nodes('/root/id') as v(parsedId)
SELECT * FROM #ParsedIds
Interestingly I've worked on an large scale system with 1000's of users and we found that using this method out performed the table-valued parameter approach for small lists of id's (no more than say 5 id's). The table-valued parameter approach was faster for larger lists of Id's.
EDIT following edited question:
Looking at your example it looks like you want to update ATable based on the Title parameter. If you can you'd benefit from rewriting your stored procedure to instead except the title parameter.
create procedure [TargetSP](
#title varchar(50)
)
as
begin
update [ATable]
set [AColumn] =
(
select [ACalculatedValue] from [AnotherTable]
)
where [ATable].[Member_Id] in (select [M].[Id] from [Member] as [M] where [M].[Title] = #title);
end
Since you only care about all the rows with a title of 'Example', you shouldn't need to determine the list first and then tell SQL Server the list you want to update, since you can already identify those with a query. So why not do this instead (I'm guessing at some data types here):
ALTER PROCEDURE dbo.TargetSP
#title VARCHAR(255)
AS
BEGIN
SET NOCOUNT ON;
-- only do this once instead of as a subquery:
DECLARE #v VARCHAR(255) = (SELECT [ACalculatedValue] From [AnotherTable]);
UPDATE a
SET AColumn = #v
FROM dbo.ATable AS a
INNER JOIN dbo.Member AS m
ON a.Member_Id = m.Id
WHERE m.Title = #title;
END
GO
Now call it as:
EXEC dbo.TargetSP #title = 'Example';
DECLARE #VId BIGINT;
DECLARE [My_Cursor] CURSOR FAST_FORWARD READ_ONLY FOR
Select [M].[Id] From [Member] AS [M] Where [M].[Title] = 'Example'
OPEN [My_Cursor]
FETCH NEXT FROM [My_Cursor] INTO #VId
WHILE ##FETCH_STATUS = 0
BEGIN
EXEC [TargetSp]
#Id = #VId
FETCH NEXT FROM [My_Cursor] INTO #VId
END
CLOSE [My_Cursor]
DEALLOCATE [My_Cursor];
GO
if the parameter is integer, you can only pass one value at a time.
Your options are:
call the proc several times, one for each parameter
Change the proc to accept a structure where you can pass more than
one id like a varchar where you pass a coma separated list of values
(not so good) or a table-value parameter
About the performance question, it would be faster to re-write the proc to iterate through a list of ids than call it several times, once per id, BUT unless you are dealing with a HUGE list of ids, I dont think you will see much of a difference
I have a stored procedure that alters user data in a certain way. I pass it user_id and it does it's thing. I want to run a query on a table and then for each user_id I find run the stored procedure once on that user_id
How would I write query for this?
use a cursor
ADDENDUM: [MS SQL cursor example]
declare #field1 int
declare #field2 int
declare cur CURSOR LOCAL for
select field1, field2 from sometable where someotherfield is null
open cur
fetch next from cur into #field1, #field2
while ##FETCH_STATUS = 0 BEGIN
--execute your sproc on each row
exec uspYourSproc #field1, #field2
fetch next from cur into #field1, #field2
END
close cur
deallocate cur
in MS SQL, here's an example article
note that cursors are slower than set-based operations, but faster than manual while-loops; more details in this SO question
ADDENDUM 2: if you will be processing more than just a few records, pull them into a temp table first and run the cursor over the temp table; this will prevent SQL from escalating into table-locks and speed up operation
ADDENDUM 3: and of course, if you can inline whatever your stored procedure is doing to each user ID and run the whole thing as a single SQL update statement, that would be optimal
try to change your method if you need to loop!
within the parent stored procedure, create a #temp table that contains the data that you need to process. Call the child stored procedure, the #temp table will be visible and you can process it, hopefully working with the entire set of data and without a cursor or loop.
this really depends on what this child stored procedure is doing. If you are UPDATE-ing, you can "update from" joining in the #temp table and do all the work in one statement without a loop. The same can be done for INSERT and DELETEs. If you need to do multiple updates with IFs you can convert those to multiple UPDATE FROM with the #temp table and use CASE statements or WHERE conditions.
When working in a database try to lose the mindset of looping, it is a real performance drain, will cause locking/blocking and slow down the processing. If you loop everywhere, your system will not scale very well, and will be very hard to speed up when users start complaining about slow refreshes.
Post the content of this procedure you want call in a loop, and I'll bet 9 out of 10 times, you could write it to work on a set of rows.
You can do it with a dynamic query.
declare #cadena varchar(max) = ''
select #cadena = #cadena + 'exec spAPI ' + ltrim(id) + ';'
from sysobjects;
exec(#cadena);
Something like this substitutions will be needed for your tables and field names.
Declare #TableUsers Table (User_ID, MyRowCount Int Identity(1,1)
Declare #i Int, #MaxI Int, #UserID nVarchar(50)
Insert into #TableUser
Select User_ID
From Users
Where (My Criteria)
Select #MaxI = ##RowCount, #i = 1
While #i <= #MaxI
Begin
Select #UserID = UserID from #TableUsers Where MyRowCount = #i
Exec prMyStoredProc #UserID
Select
#i = #i + 1, #UserID = null
End
Use a table variable or a temporary table.
As has been mentioned before, a cursor is a last resort. Mostly because it uses lots of resources, issues locks and might be a sign you're just not understanding how to use SQL properly.
Side note: I once came across a solution that used cursors to update
rows in a table. After some scrutiny, it turned out the whole thing
could be replaced with a single UPDATE command. However, in this case,
where a stored procedure should be executed, a single SQL-command
won't work.
Create a table variable like this (if you're working with lots of data or are short on memory, use a temporary table instead):
DECLARE #menus AS TABLE (
id INT IDENTITY(1,1),
parent NVARCHAR(128),
child NVARCHAR(128));
The id is important.
Replace parent and child with some good data, e.g. relevant identifiers or the whole set of data to be operated on.
Insert data in the table, e.g.:
INSERT INTO #menus (parent, child)
VALUES ('Some name', 'Child name');
...
INSERT INTO #menus (parent,child)
VALUES ('Some other name', 'Some other child name');
Declare some variables:
DECLARE #id INT = 1;
DECLARE #parentName NVARCHAR(128);
DECLARE #childName NVARCHAR(128);
And finally, create a while loop over the data in the table:
WHILE #id IS NOT NULL
BEGIN
SELECT #parentName = parent,
#childName = child
FROM #menus WHERE id = #id;
EXEC myProcedure #parent=#parentName, #child=#childName;
SELECT #id = MIN(id) FROM #menus WHERE id > #id;
END
The first select fetches data from the temporary table. The second select updates the #id. MIN returns null if no rows were selected.
An alternative approach is to loop while the table has rows, SELECT TOP 1 and remove the selected row from the temp table:
WHILE EXISTS(SELECT 1 FROM #menuIDs)
BEGIN
SELECT TOP 1 #menuID = menuID FROM #menuIDs;
EXEC myProcedure #menuID=#menuID;
DELETE FROM #menuIDs WHERE menuID = #menuID;
END;
Can this not be done with a user-defined function to replicate whatever your stored procedure is doing?
SELECT udfMyFunction(user_id), someOtherField, etc FROM MyTable WHERE WhateverCondition
where udfMyFunction is a function you make that takes in the user ID and does whatever you need to do with it.
See http://www.sqlteam.com/article/user-defined-functions for a bit more background
I agree that cursors really ought to be avoided where possible. And it usually is possible!
(of course, my answer presupposes that you're only interested in getting the output from the SP and that you're not changing the actual data. I find "alters user data in a certain way" a little ambiguous from the original question, so thought I'd offer this as a possible solution. Utterly depends on what you're doing!)
I like the dynamic query way of Dave Rincon as it does not use cursors and is small and easy. Thank you Dave for sharing.
But for my needs on Azure SQL and with a "distinct" in the query, i had to modify the code like this:
Declare #SQL nvarchar(max);
-- Set SQL Variable
-- Prepare exec command for each distinctive tenantid found in Machines
SELECT #SQL = (Select distinct 'exec dbo.sp_S2_Laser_to_cache ' +
convert(varchar(8),tenantid) + ';'
from Dim_Machine
where iscurrent = 1
FOR XML PATH(''))
--for debugging print the sql
print #SQL;
--execute the generated sql script
exec sp_executesql #SQL;
I hope this helps someone...