Array like functionality in SQL Server 2008 - sql-server

Question

I want to read EmpID in EMP Table based on some condition. For every EmpID I need to do some operation in another table. How can I read single value of EmpID at a time.
Thanks in advance

Answer 1

UPDATE otherTable...
WHERE table2.EmpID IN (SELECT EMP.EmpID FROM EMP WHERE ...)

Answer 2

try to never loop, work on sets of data.
you can insert, update, delete multiple rows at one time. here in an example insert of multiple rows:
INSERT INTO YourTable
(col1, col2, col3, col4)
SELECT
cola, colb+Colz, colc, #X
FROM ....
LEFT OUTER JOIN ...
WHERE...
you can even insert into multiple tables in a single statement:
INSERT INTO YourTable
(col1, col2, col3, col4)
OUTPUT INSERTED.PK, Inserted.Col2
INTO OtherTable (ColA, ColB)
SELECT
cola, colb+Colz, colc, #X
FROM ....
LEFT OUTER JOIN ...
WHERE...
When looking at a loop see what it done inside it. If it is just inserts/deletes/updates, re-write to use single commands. If there are IFs, see if those can be CASE statements or WHERE conditions on inserts/deletes/updates. If so, remove the loop and use set commands.
I've taken loops and replaced them with the set based commands and reduced the execution time from minutes to a few seconds. I have taken procedures with many nested loops and procedure calls and kept the loops (was impossible to only use inserts/deletes/updates), but I removed the cursor, and have seen less locking/blocking and massive performance boosts as well. Here are two looping methods that are better than cursor loops...
if you have to loop, over a set do something like this:
--this looks up each row for every iteration
DECLARE #msg VARCHAR(250)
DECLARE #hostname sysname
--first select of currsor free loop
SELECT #hostname= min(RTRIM(hostname))
FROM master.dbo.sysprocesses (NOLOCK)
WHERE hostname <> ''
WHILE #hostname is not null
BEGIN
--just some example of some odd task that requires a loop
set #msg='exec master.dbo.xp_cmdshell "net send '
+ RTRIM(#hostname) + ' '
+ 'testing "'
print #msg
--EXEC (#msg) --<<will not actually send the messages
--next select of cursor free loop
SELECT #hostname= min(RTRIM(hostname))
FROM master.dbo.sysprocesses (NOLOCK)
WHERE hostname <> ''
and hostname > #hostname
END
if you have a reasonable set of items (not 100,000) to loop over you can do this:
--this will capture each Key to loop over
DECLARE #msg VARCHAR(250)
DECLARE #From int
DECLARE #To int
CREATE TABLE #Rows --use a table #variable depending on the number of rows to handle
(
RowID int not null primary key identity(1,1)
,hostname varchar(100)
)
INSERT INTO #Rows
SELECT DISTINCT hostname
FROM master.dbo.sysprocesses (NOLOCK)
WHERE hostname <> ''
SELECT #From=0,#To=##ROWCOUNT
WHILE #From<#To
BEGIN
SET #From=#From+1
--just some example of some odd task that requires a loop
SELECT #msg='exec master.dbo.xp_cmdshell "net send '
+ RTRIM(hostname) + ' '
+ 'testing "'
FROM #Rows
WHERE RowID=#From
print #msg
--EXEC (#msg) --<<will not actually send the messages
END

Answer 3

Using a set based approach to SQL logic is always the preferred approach. In this sense DanDan's is an acceptable response.
Alternatively you could use SQL cursors. Although resource heavy they will allow you iterate through a set and apply some logic on each row.
DECLARE #EMPID char(11)
DECLARE c1 CURSOR READ_ONLY
FOR
SELECT EmpID
FROM EMP
WHERE *some_clause*
OPEN c1
FETCH NEXT FROM c1
INTO #EMPID
WHILE ##FETCH_STATUS = 0
BEGIN
PRINT #EMPID
FETCH NEXT FROM c1
INTO #EMPID
END
CLOSE c1
DEALLOCATE c1

Answer 4

Generally, you should avoid procedural code in SQL, but if you really need to, use CURSOR:
DECLARE myCursor CURSOR FAST_FORWARD
FOR
SELECT --your SQL query, a regular SQL query.
field1,
field2
FROM
table
OPEN myCursor;
FETCH NEXT FROM myCursor
INTO
#var1, --must be pre-declared, of the same types as field1
#var2
WHILE (##FETCH_STATUS = 0)
BEGIN
--your code use #var1, #var2. Perform queries, do whatever you like.
--It will loop through every row fetched by the query in the beginning of the code, and perform this.
FETCH NEXT FROM myCursor --do this exactly as before the WHILE loop
INTO
#var1,
#var2
END
CLOSE myCursor

Answer 5

Following on from DanDan's Answer, T-SQL allows you to do join in the FROM clause of an UPDATE statement (I can't remember if this is ANSI or not). EG
UPDATE
OtherTable
SET
Auditing = Employees.EmployeeName
FROM
OtherTable
INNER JOIN
Employees ON OtherTable.EmpId = Employees.EmpId
WHERE
Employees.DateStarted > '2010-09-01'