I have insert statements (simplified) in a SPROC like the following
SET ROWCOUNT 100
WHILE(1=1)
BEGIN
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
-- EDIT: Realized forgot to include this following vital line that is causing issue
SET #var = #var + ##ROWCOUNT
-- ##ROWCOUNT now takes on a value of 1, which will cause the following IF check to fail even when no lines are inserted
IF(##ROWCOUNT = 0)
BEGIN
BREAK
END
END
But the issue is, after any operation even when no more rows fit my some_condition, ##ROWCOUNT is equal to 1, not 0.
How can I break that loop when there are 0 rows returned matching my some_condition?
The "set" statement creates a row count of 1. What you should do is immediately save ##ROWCOUNT into a #rowCount variable and use that var later on.
declare #rowCount int
WHILE(1=1)
BEGIN
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
-- EDIT: Realized forgot to include this following vital line that is causing issue
SET #rowCount = ##ROWCOUNT
SET #var = #var + #rowCount
-- ##ROWCOUNT now takes on a value of 1, which will cause the following IF check to fail even when no lines are inserted
IF(#rowCount = 0)
BEGIN
BREAK
END
END
Also, you can simplify by setting #rowCount to -1 initially and changing the WHILE condition to #rowCount <> 0. The conditional BREAK will no longer be needed.
An alternative solution. This checks each iteration to see if the ID of the last inserted record has changed or not. If it hasn't changed, it indicates that no records were added that iteration.
SET ROWCOUNT 100
declare #id int;
WHILE(1=1)
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
IF(#id= ##identity)
BEGIN
BREAK
END
set #id = ##identity;
END
Try this solutions:
1st solution
Using ##ROWCOUNT in loop's condition.
SET ROWCOUNT 100
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
WHILE(##ROWCOUNT > 0)
BEGIN
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
END
2nd solition
Using goto.
SET ROWCOUNT 100
WHILE(1=1)
BEGIN
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
IF(##ROWCOUNT = 0)
BEGIN
goto label
END
END
label1:
print 'After lopp'
I think you should use select to get the ##rowcount into a variable. try this:
declare #number_of_rows int
SET ROWCOUNT 100
WHILE(1=1)
BEGIN
INSERT INTO table1
SELECT *
FROM table2
WHERE some_condition
SELECT #number_of_rows=##ROWCOUNT
IF (#number_of_rows = 0)
BEGIN
BREAK
END
END
Implemented solution similar to Moho, but used SELECT instead of SET to store ##ROWCOUNT.
Related
I am trying to do an update on a specific record every 1000 rows using Postgres. I am looking for a better way to do that. My function is described below:
CREATE OR REPLACE FUNCTION update_row()
RETURNS void AS
$BODY$
declare
myUID integer;
nRow integer;
maxUid integer;
BEGIN
nRow:=1000;
select max(uid_atm_inp) from tab into maxUid where field1 = '1240200';
loop
if (nRow > 1000 and nRow < maxUid) then
select uid from tab into myUID where field1 = '1240200' and uid >= nRow limit 1;
update tab
set field = 'xxx'
where field1 = '1240200' and uid = myUID;
nRow:=nRow+1000;
end if;
end loop;
END; $BODY$
LANGUAGE plpgsql VOLATILE
How can I improve this procedure? I think there is something wrong. The loop does not end and takes too much time.
To perform this task in SQL, you could use the row_number window function and update only those rows where the number is divisible by 1000.
Your loop doesn't finish because there is no EXIT or RETURN in it.
I doubt you could ever rival the performance of a standard SQL update with a procedural loop. Instead of doing it a row at a time, just do it all as a single statement:
with t2 as (
select
uid, row_number() over (order by 1) as rn
from tab
where field1 = '1240200'
)
update tab t1
set field = 'xxx'
from t2
where
t1.uid = t2.uid and
mod (t2.rn, 1000) = 0
Per my comment, I am presupposing what you mean by "every 1000th row," as without some designation of how to determine what tuple is what row number. That is easily edited by changing the "order by" criteria.
Adding a second where clause on the update (t1.field1 = '1240200') can't hurt but might not be necessary if these are nested loop.
This might be notionally similar to what Laurenz has in mind.
I solved this way:
declare
myUID integer;
nRow integer;
rowNum integer;
checkrow integer;
myString varchar(272);
cur_check_row cursor for select uid , row_number() over (order by 1) as rn, substr(fieldxx,1,244)
from table where field1 = '1240200' and uid >= 1000 ORDER BY uid;
BEGIN
open cur_check_row;
loop
fetch cur_check_row into myUID, rowNum, myString;
EXIT WHEN NOT FOUND;
select mod(rowNum, 1000) into checkrow;
if checkrow = 0 then
update table
set fieldxx= myString||'O'
where uid in (myUID);
end if;
end loop;
close cur_check_row;
I want to add a try catch to a while loop. The loop used while on ##ROWCOUNT > 0. In the while I have an update top (100) statement that works well without a try catch around it. When I add the try, the while ends in the first loop. What impact does the try have on ##ROWCOUNT that makes the while loop end even tough the update touched 100 records?
--do we have anything to process?
select top 1 * from SomeTable where processedFlag is null
WHILE(##ROWCOUNT > 0)
BEGIN
begin try
-- here I have an udpate top (100) statement that processes records with null flag in small batches
end try
begin catch
-- update ##ROWCOUNT so the while continues?
select top 1 * from SomeTable where processedFlag is null
end catch
END
I believe it because of
Statements such as USE, SET , DEALLOCATE CURSOR, CLOSE CURSOR,
BEGIN TRANSACTION or COMMIT TRANSACTION reset the ROWCOUNT value to 0.
May be END TRY is among them, but MSDN doesn't list all possible statements.
This will fix the problem:
DECLARE #i INT
SELECT #i = COUNT(*) FROM SomeTable WHERE processedFlag IS NULL
WHILE(#i > 0)
BEGIN
BEGIN TRY
UPDATE...
SET #i = ##ROWCOUNT
END TRY
BEGIN CATCH
SELECT #i = COUNT(*) FROM SomeTable WHERE processedFlag IS NULL
END CATCH
END
i am using if else statement and ,i want to drop the temporary table which is created out side the inner if statement , but when i execute the statement , i get the answer as , There is already an object named '#table' in the database. ---------------------MY CODE IS LIKE enter code here
DECLARE #RowCount INT;
SET #RowCount = 1;
IF #RowCount = 1
BEGIN
IF OBJECT_ID('tempdb..#Guarantor_Details') IS NOT NULL
DROP TABLE #Guarantor_Details
SELECT DISTINCT TOP 1 GUARANTORS.GUARANTOR_CODE
INTO #Guarantor_Details
FROM GUARANTORS
WHERE ISNULL(GUARANTORS.deleted, 0) <> 1;
DECLARE #GuarantorCount INT;
SELECT #GuarantorCount = count(*)
FROM #Guarantor_Details;
IF (#GuarantorCount = 0)
DROP TABLE #Guarantor_Details
BEGIN
IF OBJECT_ID('tempdb..#Guarantor_Details') IS NOT NULL
SELECT TOP 1 CLIENT.Last_Name
INTO #Guarantor_Details
FROM CLIENT
LEFT JOIN GUARANTORS ON GUARANTORS.GUARANTOR_CODE = CLIENT.Financial_Guarantor
END
END
------------------------------------------------------------------------
You don't need to do this type of CREATE / DROP. You can (and probably should) create the table before the loop and simply either TRUNCATE TABLE or DELETE FROM the temp table when necessary to "reset" it. Just pick a datatype that fits both GUARANTOR_CODE and Last_Name.
You also don't need to do a SELECT COUNT(*) on the table when you have the ##ROWCOUNT from the INSERT operation that already has that value in it.
Essentially:
CREATE TABLE #Guarantor_Details (Value NVARCHAR(50));
WHILE (something)
BEGIN
IF (#RowCount = 1)
BEGIN
TRUNCATE TABLE #Guarantor_Details;
INSERT INTO #Guarantor_Details (Value)
SELECT DISTINCT TOP 1 GUARANTORS.GUARANTOR_CODE
FROM GUARANTORS
WHERE ISNULL(GUARANTORS.deleted, 0) <> 1;
IF (##ROWCOUNT = 0)
BEGIN
INSERT INTO #Guarantor_Details (Value)
SELECT TOP 1 CLIENT.Last_Name
FROM CLIENT
LEFT JOIN GUARANTORS
ON GUARANTORS.GUARANTOR_CODE = CLIENT.Financial_Guarantor;
END;
END;
FYI, there appear to be some logic problems in the original code:
There are BEGIN / END tags at the bottom of the IF #RowCount = 1 block that aren't associated to any IF or WHILE. This is technically ok, but usually implies something is missing.
If this code is all of the code, then the IF #RowCount = 1 doesn't work in the loop unless something sets #RowCount past the end of this outer IF block that is not shown here in the question.
Link
##Rowcount is used to inform the number of rows affected for the last
select,insert,update or delete statements
declare #row int select 100 if ##rowcount>0 set #row=##rowcount ...
The above will return 0 because as soon as if ##rowcount>0 is executed
it is reset to 0 as it doesn't return any rows. So always assign to
variable first
Why does statement if ##rowcount>0 reset ##rowcount to 0? Isn't the value of ##rowcount affected only by select,insert,update and delete statements?
thank you
It is affected by the last statement. Like this SET statement
Declare #row int
select 100 union all select 200 union all select 300
set #row = ##rowcount;
SELECT #row, ##rowcount
If you read the actual Microsoft SQL Server Docs on MSDN, it gives examples of what statements affect ##ROWCOUNT. For example "such as" implies other statements like IF will also set it to zero
Statements such as USE, SET <option>, DEALLOCATE CURSOR, CLOSE CURSOR, BEGIN TRANSACTION or COMMIT TRANSACTION reset the ROWCOUNT value to 0.
Well,
I faced similar issue using sybase, which indicates that something might be wrong with "if".
declare #counter1 int
declare #counter2 int
select #counter1 = ##rowcount
if ##rowcount = 0 return
select #counter2 = ##rowcount
the output is:
counter1 = 3
counter2 = 0
I would expect 3(original one) or 1(because of Select).
This is even more strange because of
http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc38151.1540/doc/html/san1278452893271.html
"The ##rowcount is not reset to zero by any statement which does not affect rows, such as an IF statement."
on other hand there is a lot of confusion how it really works(based on discussion in internet)
At the end in my solution in first line I assign ##rowcount to variable and my logic is based on that variable
I have 3 queries. If the first one returns empty set, I execute the second query, and if it returns empty set too, I give to the server the last chance and do the third:
SELECT ... INTO #Query1
IF EXISTS(SELECT * FROM #Query1)
SELECT * FROM #Query1
ELSE BEGIN
SELECT ... INTO #Query2
IF EXISTS(SELECT * FROM #Query2)
SELECT * FROM #Query2
ELSE BEGIN
SELECT ...
END
END
It worked well, but I've faced a new task - the query should be used as a subquery as well as other queries, within IF EXISTS([subquery]). Doing this, I see
Incorrect syntax near the keyword 'INTO'.
How should I modify the original query to meet this new condition?
Regards,
Are you looking for something like this:
create function dbo.Foo()
returns #Result table ( ThingId Int, Source Int )
as
begin
insert into #Result
select ThingId, 1 as Source from Things1
if ##ROWCOUNT = 0
insert into #Result
select ThingId, 2 as Source from Things2
if ##ROWCOUNT = 0
insert into #Result
select ThingId, 3 as Source from Things3
--...
return
end
go
select * from dbo.Foo()
select 42 as 'The Answer' where exists ( select * from dbo.Foo() where Source > 9 )
You can pass parameters into the function to use in WHERE clauses and the like. The Source column may be omitted if you don't care to know where the data originated.