T SQL Looping on insert or update - sql

Question

I have two tables.
Table A and Table B. The columns are same.
create table TableA (
id int
, name varchar
, last datetime
)
create table TableB (
id int
, name varchar
, last datetime
)
I m populating table A with mass data. and i would like to either insert or update the data in table A into table B.
I d like to take the data from table A and either insert into table B if id and name doenst match or update if the id and name does match.
I tried some ETL tool but the result was very slow. I have indexing on id and name, I wanted to try this with SQL.
I have the following but not working correct:
SELECT #id = ID,
#name = name,
#LSDATE = LastSeen_DateTime
FROM DBO.A
IF EXISTS (SELECT ID, name FROM DBO.A
WHERE #ID = ID AND #name = Name)
begin
-- update
end
else
begin
--insert
end
i guess i need to put this in a loop and not quite sure how I can make this run.
Thanks.

Answer 1

Its probably faster to do it two statements one update and one insert rather than a loop
This statement updates all B rows using the data from A where the ID is the same but the name is different
Update
Update
tableB
SET
name = a.Name
From
tableB a
INNER JOIN tableA a
on b.ID = a.ID
and A.Name <> b.Name
This statement inserts all B rows into A where the id doesn't exist in A
INSERT
INSERT INTO
tableB
( ID,
Name
)
SELECT
a.ID
a.Name
FROM
tableA b
WHERE
not exists (Select A.ID From tableB a WHERE a.ID = b.ID)
Updated (reversed it from A into B rather than B into A)

Answer 2

If you were using SQL Server 2008 (or Oracle or DB2), then you could use a merge statement.
MERGE B
USING A AS source
ON (B.ID = source.ID and B.Name = source.Name)
WHEN MATCHED THEN
UPDATE SET Last = source.Last
WHEN NOT MATCHED BY TARGET THEN
INSERT (ID, Name, Last) VALUES (source.ID, source.Name, source.Last)
-- the following is optional, if you remove it, add a semicolon to the end of the above line.
OUTPUT $action,
inserted.ID AS SourceID, inserted.Name AS SourceName,
inserted.Last AS SourceLast,
deleted.ID AS TargetID, deleted.Name AS TargetName,
deleted.Last AS TargetLast ;
The bit with the "output $action" will display what rows are getting updated and what rows are getting updated.
weasel words: I recognize this isn't exactly what you were looking for, but since others may search this topic, it may be helpful for others in the future.

Answer 3

DECLARE #id int
DECLARE #name nvarchar
DECLARE #last datetime
DECLARE TableA_Cursor CURSOR FOR
select id
, name
, last
from TableA;
OPEN TableA_Cursor;
FETCH NEXT from TableA_Cursor
INTO #id, #name, #last;
WHILE ##FETCH_STATUS = 0
BEGIN
IF (EXISTS select 1 from TableB b where b.Id = #id)
update TableB
set Name = #name
, Last = #last
ELSE
insert into TableB (Id, Name, Last)
values (#id, #name, #last)
FETCH NEXT from TableA_Cursor
INTO #id, #name, #last
END
CLOSE TableA_Cursor;
DEALLOCATE TableA_Cursor;
There may be some syntax error, particularly around the IF condition, but you may get the point.