Related
I really want to learn and understand how to concatenate strings with the cursor approach.
Here is my table:
declare #t table (id int, city varchar(15))
insert into #t values
(1, 'Rome')
,(1, 'Dallas')
,(2, 'Berlin')
,(2, 'Rome')
,(2, 'Tokyo')
,(3, 'Miami')
,(3, 'Bergen')
I am trying to create a table that has all cities for each ID within one line sorted alphabetically.
ID City
1 Dallas, Rome
2 Berlin, Rome, Tokyo
3 Bergen, Miami
This is my code so far but it is not working and if somebody could walk me through each step I would be very happy and eager to learn it!
set nocount on
declare #tid int
declare #tcity varchar(15)
declare CityCursor CURSOR FOR
select * from #t
order by id, city
open CityCursor
fetch next from CityCursor into #tid, #tcity
while ( ##FETCH_STATUS = 0)
begin
if #tid = #tid -- my idea add all cities in one line within each id
print cast(#tid as varchar(2)) + ', '+ #tcity
else if #tid <> #tid --when it reaches a new id and we went through all cities it starts over for the next line
fetch next from CityCursor into #tid, #tcity
end
close CityCursor
deallocate CityCursor
select * from CityCursor
First, for future readers: A cursor, as Sean Lange wrote in his comment, is the wrong tool for this job. The correct way to do it is using a subquery with for xml.
However, since you wanted to know how to do it with a cursor, you where actually pretty close. Here is a working example:
set nocount on
declare #prevId int,
#tid int,
#tcity varchar(15)
declare #cursorResult table (id int, city varchar(32))
-- if you are expecting more than two cities for the same id,
-- the city column should be longer
declare CityCursor CURSOR FOR
select * from #t
order by id, city
open CityCursor
fetch next from CityCursor into #tid, #tcity
while ( ##FETCH_STATUS = 0)
begin
if #prevId is null or #prevId != #tid
insert into #cursorResult(id, city) values (#tid, #tcity)
else
update #cursorResult
set city = city +', '+ #tcity
where id = #tid
set #prevId = #tid
fetch next from CityCursor into #tid, #tcity
end
close CityCursor
deallocate CityCursor
select * from #cursorResult
results:
id city
1 Dallas, Rome
2 Berlin, Rome, Tokyo
3 Bergen, Miami
I've used another variable to keep the previous id value, and also inserted the results of the cursor into a table variable.
I have written nested cursor to sync with distinct city id. Although it has performance issue, you can try the following procedure
CREATE PROCEDURE USP_CITY
AS
BEGIN
set nocount on
declare #mastertid int
declare #detailstid int
declare #tcity varchar(MAX)
declare #finalCity varchar(MAX)
SET #finalCity = ''
declare #t table (id int, city varchar(max))
insert into #t values
(1, 'Rome')
,(1, 'Dallas')
,(2, 'Berlin')
,(2, 'Rome')
,(2, 'Tokyo')
,(3, 'Miami')
,(3, 'Bergen')
declare #finaltable table (id int, city varchar(max))
declare MasterCityCursor CURSOR FOR
select distinct id from #t
order by id
open MasterCityCursor
fetch next from MasterCityCursor into #mastertid
while ( ##FETCH_STATUS = 0)
begin
declare DetailsCityCursor CURSOR FOR
SELECT id,city from #t order by id
open DetailsCityCursor
fetch next from DetailsCityCursor into #detailstid,#tcity
while ( ##FETCH_STATUS = 0)
begin
if #mastertid = #detailstid
begin
SET #finalCity = #finalCity + CASE #finalCity WHEN '' THEN +'' ELSE ', ' END + #tcity
end
fetch next from DetailsCityCursor into #detailstid, #tcity
end
insert into #finaltable values(#mastertid,#finalCity)
SET #finalCity = ''
close DetailsCityCursor
deallocate DetailsCityCursor
fetch next from MasterCityCursor into #mastertid
end
close MasterCityCursor
deallocate MasterCityCursor
SELECT * FROM #finaltable
END
If you will face any problem, feel free to write in comment section. Thanks
Using a cursor for this is probably the slowest possible solution. If performance is important then there are three valid approaches. The first approach is FOR XML without special XML character protection.
declare #t table (id int, city varchar(15))
insert into #t values (1, 'Rome'),(1, 'Dallas'),(2, 'Berlin'),(2, 'Rome'),(2, 'Tokyo'),
(3, 'Miami'),(3, 'Bergen');
SELECT
t.id,
city = STUFF((
SELECT ',' + t2.city
FROM #t t2
WHERE t.id = t2.id
FOR XML PATH('')),1,1,'')
FROM #t as t
GROUP BY t.id;
The drawback to this approach is when you add a reserved XML character such as &, <, or >, you will get an XML entity back (e.g. "&" for "&"). To handle that you have to modify your query to look like this:
Sample data
IF OBJECT_ID('tempdb..#t') IS NOT NULL DROP TABLE #t;
CREATE TABLE #t (id int, words varchar(20))
INSERT #t VALUES (1, 'blah blah'),(1, 'yada yada'),(2, 'PB&J'),(2,' is good');
SELECT
t.id,
city = STUFF((
SELECT ',' + t2.words
FROM #t t2
WHERE t.id = t2.id
FOR XML PATH(''), TYPE).value('.','varchar(1000)'),1,1,'')
FROM #t as t
GROUP BY t.id;
The downside to this approach is that it will be slower. The good news (and another reason this approach is 100 times better than a cursor) is that both of these queries benefit greatly when the optimizer chooses a parallel execution plan.
The best approach is a new fabulous function available in SQL Server 2017, STRING_AGG. STRING_AGG does not have the problem with special XML characters and is, by far the cleanest approach:
SELECT t.id, STRING_AGG(t.words,',') WITHIN GROUP (ORDER BY t.id)
FROM #t as t
GROUP BY t.id;
I'm using MSQL 2005. I have 2 table.A and B
Table A
- ID DOVKOD
- 1 KURSATIS
Table B
- ID KURALIS KURSATIS
- 1 2,2522 2,2685
- 2 2,4758 2,4874
Table A has only 1 record
When I execute Select (Select DOVKOD from Table A) from Table B I want to get same result as Select KURSATIS from Table B
I am gonna use it in a view. How can I do that. Thanks..
You can simply use a CASE expression:
SELECT CASE WHEN (SELECT DOVKOD FROM A) = 'KURSATIS' THEN KURSATIS
ELSE KURALIS
END
FROM B
SQL Fiddle Demo here
You must use Dynamic TSQL
SELECT #column=DOVKOD from Table A
EXEC ('Select ' + #column + ' from Table B')
If I understood you right then in table A you have the name of the column that you want to return. Then your solution is bad at all. I'll rather do something like that:
CREATE TABLE #TableA
(
ID INT, DOVKOD VARCHAR(100)
);
INSERT INTO #TableA VALUES (1, 'KURSATIS');
CREATE TABLE #TableB
(
ID INT, Value DECIMAL (18,2),Name VARCHAR(100)
);
INSERT INTO #TableB VALUES (1, 2.2522 , 'KURALIS');
INSERT INTO #TableB VALUES (2, 2.4758 , 'KURSATIS');
SELECT #TableB.* FROM #TableB JOIN #TableA ON #TableA.DOVKOD = #TableB.Name
The only way how to do this in MySQL is using Prepared statements. Dynamic pivot tables (transform rows to columns) is a good article about this.
SET #sql = NULL;
Select DOVKOD INTO #sql
FROM from Table A;
SET #sql = CONCAT('SELECT ', #sql, 'FROM Table B');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
I have a table as follows
cat_id Cat_Name Main_Cat_Id
1 veg null
2 main course 1
3 starter 1
4 Indian 2
5 mexican 2
6 tahi 3
7 chinese 3
8 nonveg null
9 main course 8
10 indian 9
11 starter 8
12 tahi 11
13 chinese 11
(Main_Cat_Id is cat_id of previously added category in which it belongs)
This table is used for the categories the product where veg category has the two sub category main course and starter which is identify by main_cat_id
and those subcategories again has sub category as indian and mexican
And this categorization is dependent on the user; he can add more sub categories to indian, mexican also so that he can have any level of categorization
now I have to select all the subcategories of any node like if I take veg i have to select
(1)veg > (2)main course(1) > (4)indian(2)
> (5)mexican(2)
> (3)starter(1) > (6)thai(3)
> (7)chinese(3)
to form the string as 1,2,4,5,3,6,7
to do this i wrote a sql function as
CREATE FUNCTION [dbo].[GetSubCategory_TEST]
( #MainCategory int, #Category varchar(max))
RETURNS varchar(max)
AS
BEGIN
IF EXISTS (SELECT Cat_Id FROM Category WHERE Main_Cat_Id=#MainCategory)
BEGIN
DECLARE #TEMP TABLE
(
CAT_ID INT
)
INSERT INTO #TEMP(CAT_ID) SELECT Cat_Id FROM Category WHERE Main_Cat_Id=#MainCategory
DECLARE #TEMP_CAT_ID INT
DECLARE CUR_CAT_ID CURSOR FOR SELECT CAT_ID FROM #TEMP
OPEN CUR_CAT_ID
WHILE 1 =1
BEGIN
FETCH NEXT FROM CUR_CAT_ID
INTO #TEMP_CAT_ID;
IF ##FETCH_STATUS <> 0
SET #Category=#Category+','+ CONVERT(VARCHAR(50), #TEMP_CAT_ID)
SET #Category = [dbo].[GetSubCategory](#TEMP_CAT_ID,#Category)
END
CLOSE CUR_CAT_ID
DEALLOCATE CUR_CAT_ID
END
return #Category
END
but this function keep on executing and not gives the desired output i don't understands what wrong is going on plz help me to get this
You dont need a recursive function to build this, you can use a Recursive CTE for that.
Something like
DECLARE #TABLE TABLE(
cat_id INT,
Cat_Name VARCHAR(50),
Main_Cat_Id INT
)
INSERT INTO #TABLE SELECT 1,'veg',null
INSERT INTO #TABLE SELECT 2,'main course',1
INSERT INTO #TABLE SELECT 3,'starter',1
INSERT INTO #TABLE SELECT 4,'Indian',2
INSERT INTO #TABLE SELECT 5,'mexican',2
INSERT INTO #TABLE SELECT 6,'tahi',3
INSERT INTO #TABLE SELECT 7,'chinese',3
INSERT INTO #TABLE SELECT 8,'nonveg',null
INSERT INTO #TABLE SELECT 9,'main course',8
INSERT INTO #TABLE SELECT 10,'indian',9
INSERT INTO #TABLE SELECT 11,'starter',8
INSERT INTO #TABLE SELECT 12,'tahi',11
INSERT INTO #TABLE SELECT 13,'chinese',11
;WITH Recursives AS (
SELECT *,
CAST(cat_id AS VARCHAR(MAX)) + '\' ID_Path
FROM #TABLE
WHERE Main_Cat_Id IS NULL
UNION ALL
SELECT t.*,
r.ID_Path + CAST(t.cat_id AS VARCHAR(MAX)) + '\'
FROM #TABLE t INNER JOIN
Recursives r ON t.Main_Cat_Id = r.cat_id
)
SELECT *
FROM Recursives
I am ashamed, but I used #astander scipt to give string result.
First I created data you gave.
Second I collect rows which I need
And then using XML I put everything in one row (function STUFF removes first comma)
DECLARE #TABLE TABLE(
cat_id INT,
Cat_Name VARCHAR(50),
Main_Cat_Id INT
)
DECLARE #Collected TABLE(
cat_id INT
)
INSERT INTO #TABLE SELECT 1,'veg',null
INSERT INTO #TABLE SELECT 2,'main course',1
INSERT INTO #TABLE SELECT 3,'starter',1
INSERT INTO #TABLE SELECT 4,'Indian',2
INSERT INTO #TABLE SELECT 5,'mexican',2
INSERT INTO #TABLE SELECT 6,'tahi',3
INSERT INTO #TABLE SELECT 7,'chinese',3
INSERT INTO #TABLE SELECT 8,'nonveg',null
INSERT INTO #TABLE SELECT 9,'main course',8
INSERT INTO #TABLE SELECT 10,'indian',9
INSERT INTO #TABLE SELECT 11,'starter',8
INSERT INTO #TABLE SELECT 12,'tahi',11
INSERT INTO #TABLE SELECT 13,'chinese',11
INSERT INTO #TABLE SELECT 14,'chinese',6
DECLARE #nodeID INT = 1;
DECLARE #result VARCHAR(MAX);
;WITH Recursives AS (
SELECT cat_id, main_cat_id
FROM #TABLE
WHERE Cat_Id = #nodeID
UNION ALL
SELECT T.cat_id, T.main_cat_id
FROM #TABLE AS T
INNER JOIN Recursives AS R
ON t.Main_Cat_Id = r.cat_id
)
INSERT INTO #Collected
SELECT cat_id
FROM Recursives
SELECT #result = STUFF(
(SELECT ',' + CAST( cat_id AS VARCHAR)
FROM #Collected
ORDER BY cat_id
FOR XML PATH('')
), 1,1,'')
SELECT #result
Your cursor is looping infinitely because you asked it to keep going until 1 no longer equals 1:
WHILE 1 =1
1=1 is always true so the loop never ends, and you don't explicitly break out of it anywhere.
You would do well to study some examples of cursors, for example this one in the Microsoft T-SQL documentation. They are quite formulaic and the main syntax rarely needs to vary much.
The standard approach after opening the cursor is to do an initial fetch next to get the first result, then open a while loop conditional on ##FETCH_STATUS = 0 (0 meaning successful).
Because you're looking only for unsuccessful cursor fetch states inside your cursor:
IF ##FETCH_STATUS <> 0
The setting of #Category will only happen once the cursor has gone past the last row in the set. I suspect this is exactly what you don't want.
I'm also not sure about the scoping of the #Category variable, since it's an input parameter to the function; I generally create new variables inside a function to work with, but off the top of my head I'm not sure this will actually create a problem or not.
More generally, although I don't totally understand what you're trying to achieve here, a recursive function involving a cursor is probably not the right way to do it, as Adriaan Stander's answer suggests.
given this table and data:
DECLARE #Table table (RowID int, RowCode char(1), RowValue int);set nocount on
INSERT #Table VALUES ( 6,'A',3757 )
INSERT #Table VALUES ( 5,'A',37827)
INSERT #Table VALUES (14,'A',48411)
INSERT #Table VALUES ( 1,'A',48386)
INSERT #Table VALUES (20,'A',48450)
INSERT #Table VALUES ( 7,'A',46155)
INSERT #Table VALUES (13,'A',721 )
INSERT #Table VALUES ( 2,'A',49335)
INSERT #Table VALUES (15,'A',4700 )
INSERT #Table VALUES (19,'A',64416)
INSERT #Table VALUES ( 8,'A',27246)
INSERT #Table VALUES (12,'B',54929)
INSERT #Table VALUES (16,'B',3872 )
INSERT #Table VALUES ( 3,'C',728 )
INSERT #Table VALUES (11,'C',1050 )
INSERT #Table VALUES ( 9,'C',3191 )
INSERT #Table VALUES (17,'C',866 )
INSERT #Table VALUES ( 4,'C',838 )
INSERT #Table VALUES (10,'D',550 )
INSERT #Table VALUES (18,'D',1434 );set nocount off
I need this:
VVVVVVVV
RowID RowCode RowValue RowChunk
----- ------- -------- --------
1 A 48386 1
2 A 49335 1
5 A 37827 1
6 A 3757 1
7 A 46155 1
8 A 27246 2
13 A 721 2
14 A 48411 2
15 A 4700 2
19 A 64416 2
20 A 48450 3
12 B 54929 4
16 B 3872 4
3 C 728 5
4 C 838 5
9 C 3191 5
11 C 1050 5
17 C 866 5
10 D 550 6
18 D 1434 6
RowChunk starts at 1 and is incremented by 1 for each RowCode change and/or when there have been 5 of the same RowCode values.
Basically my solution uses the same approach as yours, only with slightly different devices employed.
WITH NumberedRows AS (
SELECT
RowID,
RowCode,
RowValue,
CodeChunk = (ROW_NUMBER() OVER (PARTITION BY RowCode ORDER BY RowID) - 1) / 5
FROM #Table
)
SELECT
RowID,
RowCode,
RowValue,
RowChunk = DENSE_RANK() OVER (ORDER BY RowCode, CodeChunk)
FROM NumberedRows
I don't think there's an analysis function, or any reasonable combination of such, which will address this. You'll have to do it RBAR with a cursor or, slightly faster in my experience, a loop.
This example of looping assumes that RowID is unique. If RowID is not the clustered PK, this will be very slow, so if that's the case you'll want to create a temp table.
DECLARE #RowID INT = (SELECT MIN(RowID) FROM #Table)
DECLARE #MaxRowID INT = (SELECT MAX(RowID) FROM #Table)
DECLARE #RowCode CHAR(1)
DECLARE #LastRowCode CHAR(1)
DECLARE #RowValue INT
DECLARE #Chunk INT = 0
DECLARE #RecsThisChunk INT
DECLARE #Results TABLE (RowID INT NOT NULL PRIMARY KEY, RowCode CHAR(1) NOT NULL, RowValue INT NOT NULL, Chunk INT NOT NULL)
WHILE #RowID <= #MaxRowID
BEGIN
-- Handle gaps in RowID
IF NOT EXISTS (SELECT * FROM #Table WHERE RowID = #RowID) GOTO EndOfLoop
-- Load values for this record
SELECT #RowCode = RowCode, #RowValue = RowValue FROM #Table WHERE RowID = #RowID
IF #LastRowCode IS NULL OR #RowCode <> #LastRowCode OR #RecsThisChunk = 5
BEGIN
-- Start a new chunk
SET #Chunk = #Chunk + 1
SET #RecsThisChunk = 1
END
ELSE
BEGIN
-- Same chunk
SET #RecsThisChunk = #RecsThisChunk + 1
END
SET #LastRowCode = #RowCode
INSERT INTO #Results (RowID, RowCode, RowValue, Chunk) VALUES (#RowID, #RowCode, #RowValue, #Chunk)
EndOfLoop:
SET #RowID = #RowID + 1
END
SELECT * FROM #Results
You may have tweak this a bit for 2005, I use 2008 routinely and don't recall all the little differences.
FYI, the results you show don't quite match the sample data.
Hope this helps! The only alternative I see is a cursor, or handling this in the application layer.
this does the trick without a loop:
;WITH NumberedRows AS (
SELECT
r.RowID, r.RowCode, r.RowValue, CEILING(ROW_NUMBER() OVER(PARTITION BY r.RowCode ORDER BY r.RowCode,r.RowID)/5.0) AS CodeRowChunk
FROM #Table r
)
, AllChunks AS (
SELECT r.*,ROW_NUMBER() OVER(ORDER BY RowCode,CodeRowChunk) AS ChunkRowNumber
FROM (SELECT DISTINCT
RowCode, CodeRowChunk
FROM NumberedRows) r
)
SELECT
a.RowID, RowCode, a.RowValue,
(SELECT ChunkRowNumber FROM AllChunks c WHERE c.RowCode=a.RowCode and c.CodeRowChunk=a.CodeRowChunk) AS RowChunk
FROM NumberedRows a
This is the answer you are looking for :
create Table [table] (RowID int, RowCode char(1), RowValue int)
INSERT [Table] VALUES ( 6,'A',3757 )
INSERT [Table] VALUES ( 5,'A',37827)
INSERT [Table] VALUES (14,'A',48411)
INSERT [Table] VALUES ( 1,'A',48386)
INSERT [Table] VALUES (20,'A',48450)
INSERT [Table] VALUES ( 7,'A',46155)
INSERT [Table] VALUES (13,'A',721 )
INSERT [Table] VALUES ( 2,'A',49335)
INSERT [Table] VALUES (15,'A',4700 )
INSERT [Table] VALUES (19,'A',64416)
INSERT [Table] VALUES ( 8,'A',27246)
INSERT [Table] VALUES (12,'B',54929)
INSERT [Table] VALUES (16,'B',3872 )
INSERT [Table] VALUES ( 3,'C',728 )
INSERT [Table] VALUES (11,'C',1050 )
INSERT [Table] VALUES ( 9,'C',3191 )
INSERT [Table] VALUES (17,'C',866 )
INSERT [Table] VALUES ( 4,'C',838 )
INSERT [Table] VALUES (10,'D',550 )
INSERT [Table] VALUES (18,'D',1434 )
IF object_id('tempdb..#tempTable') IS NOT NULL
BEGIN
DROP TABLE #tempTable
END
CREATE TABLE #tempTable
(RowID int, RowCode char(1), RowValue int,RowChunk int)
INSERT INTO #tempTable
select RowID,RowCode,RowValue,null from [table]
declare #RowId int
declare #RowCode char(1)
declare #Count int
declare #CurrentCode char(1)
declare #CountCurrent int
set #Count=1
set #CurrentCode=1
set #CountCurrent=0
DECLARE contact_cursor CURSOR FOR
SELECT RowID,RowCode FROM [table]
OPEN contact_cursor
FETCH NEXT FROM contact_cursor into #RowId,#RowCode
set #CurrentCode=#RowCode
WHILE ##FETCH_STATUS = 0
BEGIN
if(#CurrentCode=#RowCode)
begin
if(#CountCurrent=5)
begin
set #CountCurrent=1
set #Count=#Count+1
update #tempTable set RowChunk=#Count where RowID=#RowID
end
else
begin
set #CountCurrent=#CountCurrent+1
update #tempTable set RowChunk=#Count where RowID=#RowID
end
end
else
begin
set #CurrentCode=#RowCode
set #CountCurrent=1
set #Count=#Count+1
update #tempTable set RowChunk=#Count where RowID=#RowID
end
FETCH NEXT FROM contact_cursor into #RowId,#RowCode
END
CLOSE contact_cursor
DEALLOCATE contact_cursor
select * from #tempTable
GO
Let's say I have the following simple table variable:
declare #databases table
(
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into #databases
Is declaring and using a cursor my only option if I wanted to iterate through the rows? Is there another way?
First of all you should be absolutely sure you need to iterate through each row — set based operations will perform faster in every case I can think of and will normally use simpler code.
Depending on your data it may be possible to loop using just SELECT statements as shown below:
Declare #Id int
While (Select Count(*) From ATable Where Processed = 0) > 0
Begin
Select Top 1 #Id = Id From ATable Where Processed = 0
--Do some processing here
Update ATable Set Processed = 1 Where Id = #Id
End
Another alternative is to use a temporary table:
Select *
Into #Temp
From ATable
Declare #Id int
While (Select Count(*) From #Temp) > 0
Begin
Select Top 1 #Id = Id From #Temp
--Do some processing here
Delete #Temp Where Id = #Id
End
The option you should choose really depends on the structure and volume of your data.
Note: If you are using SQL Server you would be better served using:
WHILE EXISTS(SELECT * FROM #Temp)
Using COUNT will have to touch every single row in the table, the EXISTS only needs to touch the first one (see Josef's answer below).
Just a quick note, if you are using SQL Server (2008 and above), the examples that have:
While (Select Count(*) From #Temp) > 0
Would be better served with
While EXISTS(SELECT * From #Temp)
The Count will have to touch every single row in the table, the EXISTS only needs to touch the first one.
This is how I do it:
declare #RowNum int, #CustId nchar(5), #Name1 nchar(25)
select #CustId=MAX(USERID) FROM UserIDs --start with the highest ID
Select #RowNum = Count(*) From UserIDs --get total number of records
WHILE #RowNum > 0 --loop until no more records
BEGIN
select #Name1 = username1 from UserIDs where USERID= #CustID --get other info from that row
print cast(#RowNum as char(12)) + ' ' + #CustId + ' ' + #Name1 --do whatever
select top 1 #CustId=USERID from UserIDs where USERID < #CustID order by USERID desc--get the next one
set #RowNum = #RowNum - 1 --decrease count
END
No Cursors, no temporary tables, no extra columns.
The USERID column must be a unique integer, as most Primary Keys are.
Define your temp table like this -
declare #databases table
(
RowID int not null identity(1,1) primary key,
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into #databases
Then do this -
declare #i int
select #i = min(RowID) from #databases
declare #max int
select #max = max(RowID) from #databases
while #i <= #max begin
select DatabaseID, Name, Server from #database where RowID = #i --do some stuff
set #i = #i + 1
end
Here is how I would do it:
Select Identity(int, 1,1) AS PK, DatabaseID
Into #T
From #databases
Declare #maxPK int;Select #maxPK = MAX(PK) From #T
Declare #pk int;Set #pk = 1
While #pk <= #maxPK
Begin
-- Get one record
Select DatabaseID, Name, Server
From #databases
Where DatabaseID = (Select DatabaseID From #T Where PK = #pk)
--Do some processing here
--
Select #pk = #pk + 1
End
[Edit] Because I probably skipped the word "variable" when I first time read the question, here is an updated response...
declare #databases table
(
PK int IDENTITY(1,1),
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into #databases
--/*
INSERT INTO #databases (DatabaseID, Name, Server) SELECT 1,'MainDB', 'MyServer'
INSERT INTO #databases (DatabaseID, Name, Server) SELECT 1,'MyDB', 'MyServer2'
--*/
Declare #maxPK int;Select #maxPK = MAX(PK) From #databases
Declare #pk int;Set #pk = 1
While #pk <= #maxPK
Begin
/* Get one record (you can read the values into some variables) */
Select DatabaseID, Name, Server
From #databases
Where PK = #pk
/* Do some processing here */
/* ... */
Select #pk = #pk + 1
End
If you have no choice than to go row by row creating a FAST_FORWARD cursor. It will be as fast as building up a while loop and much easier to maintain over the long haul.
FAST_FORWARD
Specifies a FORWARD_ONLY, READ_ONLY cursor with performance optimizations enabled. FAST_FORWARD cannot be specified if SCROLL or FOR_UPDATE is also specified.
This will work in SQL SERVER 2012 version.
declare #Rowcount int
select #Rowcount=count(*) from AddressTable;
while( #Rowcount>0)
begin
select #Rowcount=#Rowcount-1;
SELECT * FROM AddressTable order by AddressId desc OFFSET #Rowcount ROWS FETCH NEXT 1 ROWS ONLY;
end
Another approach without having to change your schema or using temp tables:
DECLARE #rowCount int = 0
,#currentRow int = 1
,#databaseID int
,#name varchar(15)
,#server varchar(15);
SELECT #rowCount = COUNT(*)
FROM #databases;
WHILE (#currentRow <= #rowCount)
BEGIN
SELECT TOP 1
#databaseID = rt.[DatabaseID]
,#name = rt.[Name]
,#server = rt.[Server]
FROM (
SELECT ROW_NUMBER() OVER (
ORDER BY t.[DatabaseID], t.[Name], t.[Server]
) AS [RowNumber]
,t.[DatabaseID]
,t.[Name]
,t.[Server]
FROM #databases t
) rt
WHERE rt.[RowNumber] = #currentRow;
EXEC [your_stored_procedure] #databaseID, #name, #server;
SET #currentRow = #currentRow + 1;
END
You can use a while loop:
While (Select Count(*) From #TempTable) > 0
Begin
Insert Into #Databases...
Delete From #TempTable Where x = x
End
Lightweight, without having to make extra tables, if you have an integer ID on the table
Declare #id int = 0, #anything nvarchar(max)
WHILE(1=1) BEGIN
Select Top 1 #anything=[Anything],#id=#id+1 FROM Table WHERE ID>#id
if(##ROWCOUNT=0) break;
--Process #anything
END
I really do not see the point why you would need to resort to using dreaded cursor.
But here is another option if you are using SQL Server version 2005/2008
Use Recursion
declare #databases table
(
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
--; Insert records into #databases...
--; Recurse through #databases
;with DBs as (
select * from #databases where DatabaseID = 1
union all
select A.* from #databases A
inner join DBs B on A.DatabaseID = B.DatabaseID + 1
)
select * from DBs
-- [PO_RollBackOnReject] 'FININV10532'
alter procedure PO_RollBackOnReject
#CaseID nvarchar(100)
AS
Begin
SELECT *
INTO #tmpTable
FROM PO_InvoiceItems where CaseID = #CaseID
Declare #Id int
Declare #PO_No int
Declare #Current_Balance Money
While (Select ROW_NUMBER() OVER(ORDER BY PO_LineNo DESC) From #tmpTable) > 0
Begin
Select Top 1 #Id = PO_LineNo, #Current_Balance = Current_Balance,
#PO_No = PO_No
From #Temp
update PO_Details
Set Current_Balance = Current_Balance + #Current_Balance,
Previous_App_Amount= Previous_App_Amount + #Current_Balance,
Is_Processed = 0
Where PO_LineNumber = #Id
AND PO_No = #PO_No
update PO_InvoiceItems
Set IsVisible = 0,
Is_Processed= 0
,Is_InProgress = 0 ,
Is_Active = 0
Where PO_LineNo = #Id
AND PO_No = #PO_No
End
End
It's possible to use a cursor to do this:
create function [dbo].f_teste_loop
returns #tabela table
(
cod int,
nome varchar(10)
)
as
begin
insert into #tabela values (1, 'verde');
insert into #tabela values (2, 'amarelo');
insert into #tabela values (3, 'azul');
insert into #tabela values (4, 'branco');
return;
end
create procedure [dbo].[sp_teste_loop]
as
begin
DECLARE #cod int, #nome varchar(10);
DECLARE curLoop CURSOR STATIC LOCAL
FOR
SELECT
cod
,nome
FROM
dbo.f_teste_loop();
OPEN curLoop;
FETCH NEXT FROM curLoop
INTO #cod, #nome;
WHILE (##FETCH_STATUS = 0)
BEGIN
PRINT #nome;
FETCH NEXT FROM curLoop
INTO #cod, #nome;
END
CLOSE curLoop;
DEALLOCATE curLoop;
end
I'm going to provide the set-based solution.
insert #databases (DatabaseID, Name, Server)
select DatabaseID, Name, Server
From ... (Use whatever query you would have used in the loop or cursor)
This is far faster than any looping techique and is easier to write and maintain.
I prefer using the Offset Fetch if you have a unique ID you can sort your table by:
DECLARE #TableVariable (ID int, Name varchar(50));
DECLARE #RecordCount int;
SELECT #RecordCount = COUNT(*) FROM #TableVariable;
WHILE #RecordCount > 0
BEGIN
SELECT ID, Name FROM #TableVariable ORDER BY ID OFFSET #RecordCount - 1 FETCH NEXT 1 ROW;
SET #RecordCount = #RecordCount - 1;
END
This way I don't need to add fields to the table or use a window function.
I agree with the previous post that set-based operations will typically perform better, but if you do need to iterate over the rows here's the approach I would take:
Add a new field to your table variable (Data Type Bit, default 0)
Insert your data
Select the Top 1 Row where fUsed = 0 (Note: fUsed is the name of the field in step 1)
Perform whatever processing you need to do
Update the record in your table variable by setting fUsed = 1 for the record
Select the next unused record from the table and repeat the process
DECLARE #databases TABLE
(
DatabaseID int,
Name varchar(15),
Server varchar(15),
fUsed BIT DEFAULT 0
)
-- insert a bunch rows into #databases
DECLARE #DBID INT
SELECT TOP 1 #DBID = DatabaseID from #databases where fUsed = 0
WHILE ##ROWCOUNT <> 0 and #DBID IS NOT NULL
BEGIN
-- Perform your processing here
--Update the record to "used"
UPDATE #databases SET fUsed = 1 WHERE DatabaseID = #DBID
--Get the next record
SELECT TOP 1 #DBID = DatabaseID from #databases where fUsed = 0
END
Step1: Below select statement creates a temp table with unique row number for each record.
select eno,ename,eaddress,mobno int,row_number() over(order by eno desc) as rno into #tmp_sri from emp
Step2:Declare required variables
DECLARE #ROWNUMBER INT
DECLARE #ename varchar(100)
Step3: Take total rows count from temp table
SELECT #ROWNUMBER = COUNT(*) FROM #tmp_sri
declare #rno int
Step4: Loop temp table based on unique row number create in temp
while #rownumber>0
begin
set #rno=#rownumber
select #ename=ename from #tmp_sri where rno=#rno **// You can take columns data from here as many as you want**
set #rownumber=#rownumber-1
print #ename **// instead of printing, you can write insert, update, delete statements**
end
This approach only requires one variable and does not delete any rows from #databases. I know there are a lot of answers here, but I don't see one that uses MIN to get your next ID like this.
DECLARE #databases TABLE
(
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into #databases
DECLARE #CurrID INT
SELECT #CurrID = MIN(DatabaseID)
FROM #databases
WHILE #CurrID IS NOT NULL
BEGIN
-- Do stuff for #CurrID
SELECT #CurrID = MIN(DatabaseID)
FROM #databases
WHERE DatabaseID > #CurrID
END
Here's my solution, which makes use of an infinite loop, the BREAK statement, and the ##ROWCOUNT function. No cursors or temporary table are necessary, and I only need to write one query to get the next row in the #databases table:
declare #databases table
(
DatabaseID int,
[Name] varchar(15),
[Server] varchar(15)
);
-- Populate the [#databases] table with test data.
insert into #databases (DatabaseID, [Name], [Server])
select X.DatabaseID, X.[Name], X.[Server]
from (values
(1, 'Roger', 'ServerA'),
(5, 'Suzy', 'ServerB'),
(8675309, 'Jenny', 'TommyTutone')
) X (DatabaseID, [Name], [Server])
-- Create an infinite loop & ensure that a break condition is reached in the loop code.
declare #databaseId int;
while (1=1)
begin
-- Get the next database ID.
select top(1) #databaseId = DatabaseId
from #databases
where DatabaseId > isnull(#databaseId, 0);
-- If no rows were found by the preceding SQL query, you're done; exit the WHILE loop.
if (##ROWCOUNT = 0) break;
-- Otherwise, do whatever you need to do with the current [#databases] table row here.
print 'Processing #databaseId #' + cast(#databaseId as varchar(50));
end
This is the code that I am using 2008 R2. This code that I am using is to build indexes on key fields (SSNO & EMPR_NO) n all tales
if object_ID('tempdb..#a')is not NULL drop table #a
select 'IF EXISTS (SELECT name FROM sysindexes WHERE name ='+CHAR(39)+''+'IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+char(39)+')'
+' begin DROP INDEX [IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+'] ON '+table_schema+'.'+table_name+' END Create index IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+ ' on '+ table_schema+'.'+table_name+' ('+COLUMN_NAME+') ' 'Field'
,ROW_NUMBER() over (order by table_NAMe) as 'ROWNMBR'
into #a
from INFORMATION_SCHEMA.COLUMNS
where (COLUMN_NAME like '%_SSNO_%' or COLUMN_NAME like'%_EMPR_NO_')
and TABLE_SCHEMA='dbo'
declare #loopcntr int
declare #ROW int
declare #String nvarchar(1000)
set #loopcntr=(select count(*) from #a)
set #ROW=1
while (#ROW <= #loopcntr)
begin
select top 1 #String=a.Field
from #A a
where a.ROWNMBR = #ROW
execute sp_executesql #String
set #ROW = #ROW + 1
end
SELECT #pk = #pk + 1
would be better:
SET #pk += #pk
Avoid using SELECT if you are not referencing tables are are just assigning values.