Adding daily changes to database table - sql

Question

I am trying to build a simple database that keeps track of any changes to a users location attribute. Each day I generate the current information of User,Date,Location and upload to a temporary table in sql server. I am trying to figure out the correct sql to query for new users, modified users and deleted users.
Finding new users is easy with:
SELECT table1.UserGuid,table1.Location
FROM table1
WHERE table1.UserGuid NOT IN
(
SELECT DISTINCT table2.UserGuid
FROM table2
)
The problem I am having is finding modified locations and deleted users.
For modified users I am trying to return users where their last location in the database doesn't match the current location in the daily temp database. This is what i have but i don't think it is correct:
SELECT table1.UserGuid,table1.Location
FROM table1
WHERE EXISTS
(
SELECT TOP 1 table2.UserGuid,table2.Location
FROM table2
WHERE (table2.UserGuid = table1.UserGuid) AND (table2.Location != table1.Location)
ORDER BY table2.Date DESC
)
For deleted users, I am trying the following sql to identify any Users in the main table that doesn't exist in the daily temp table and don't have a location of deleted. (if this returns any deleted users then I add them to the main table with a location of deleted so they are not returned the next time)
SELECT table2.UserGuid,table2.Location
FROM table2
WHERE table2.UserGuid NOT IN
(
SELECT UserGuid
FROM table1
)
AND table2.Location != 'deleted'
after I run all 3 queries to find the adds, modifications and deletes I add them to the main table along with the current date and repeat the next day. So the main table has 3 columns (UserGuid, Date, Location) and new rows get added each day with changed information. So far my New user sql is the only one working reliably. Is there an easier way to do this?

Answer 1

So I think this captures all your requirements.
Select
table1.*,
case when table2.userguid is null then 'INSERT'
when table1.userguid is null and table2.location != 'deleted' then 'DELETE'
when table1.location != table2.location then 'UPDATE'
from table1
full join (select max(date) as lastEntry, userGuid from Table2) lastRecords
inner join table2 on table2.date = lastRecords.lastEntry and table2.userGuid = lastRecords.userGuid
on lastRecords.userguid = table1.userguid

Answer 2

For your second query try:
SELECT table1.UserGuid,table1.Location
FROM table1
WHERE table1.UserGuid IN
(
SELECT table2.UserGuid
FROM table2
WHERE table2.UserGuid = table2.UserGuid AND table2.Location <> table2.Location
)

Answer 3

I tend to use EXISTS for these sorts of checks
--INSERTS
SELECT table1.UserGuid,table1.Location
FROM table1
WHERE NOT EXISTS (SELECT 1 FROM table2 WHERE table2.UserGuid = table1.UserGuid)
UNION ALL
--UPDATES
SELECT table1.UserGuid,table1.Location
FROM table1
WHERE EXISTS
(
SELECT 1 FROM table2
WHERE table2.UserGuid = table1.UserGuid
AND ISNULL(table2.Location,'') <> ISNULL(table1.Location,'')
)
UNION ALL
--DELETES
SELECT table2.UserGuid,table2.Location
FROM table2
WHERE NOT EXISTS (SELECT 1 FROM table1 WHERE table2.UserGuid = table1.UserGuid)
I included ISNULL checks in the event your location could be null; they're not needed if that's not possible.