I am trying to use update / where in a sql query to match ID's and then pull the data associated into my table.
I am running into a problem.
First, when I run
UPDATE table1
SET table1.column = table2.column
FROM table2
WHERE table1.columnB = table2.columnB
it works on some and not others. its like 50/50 success. Some of the results are completely wrong and I don't know why.
Thanks for the help.
The only reason that I can think of is that the join is not one-to-one. That is, there are mutliple rows in table2 that match each row in table1. In this case, the results come from an arbitrary row.
Related
We have two tables we want to merge. Say, table1 and table2.
They have the exact same columns, and the exact same purpose. The difference being table2 having newer data.
We used a query that uses LEFT JOIN to find the the rows that are common between them, and skip those rows while merging. The problem is this. both tables have 500M rows.
When we ran the query, it kept going on and on. For an hour it just kept running. We were certain this was because of the large number of rows.
But when we wanted to see how many rows were already inserted to table2, we ran the code select count(*) from table2, it gave us the exact same row count of table2 as when we started.
Our questions is, is that how it's supposed to be? Do the rows get inserted all at the same time after all the matches have been found?
If you would like to read uncommited data, than the count should me modified, like this:
select count(*) from table2 WITH (NOLOCK)
NOLOCK is over-used, but in this specific scenario, it might be handy.
No data are inserted or updated one by one.
I have no idea how it is related with "Select count(*) from table2 WITH (NOLOCK) "
Join condition is taking too long to produce Resultset which will be use by insert operator .So actually there is no insert because no resultset is being produce.
Join query is taking too long because Left Join condition produces very very high cardinality estimate.
so one has to fix Join condition first.
for that need other info like Table schema ,Data type and length and existing index,requirement.
I... don't quite know if I have the right idea about Access here.
I wrote the following, to grab some data that existed in two places:-
Select TableOne.*
from TableOne inner join TableTwo
on TableOne.[LINK] = TableTwo.[LINK]
Now, my interpretation of this is:
Find the table "TableOne"
Match the LINK field to the corresponding field in the table "TableTwo"
Show only records from TableOne that have a matching record in TableTwo
Just to make sure, I ran the query with some sample tables in SSMS, and it worked as expected.
So why, when I deleted the rows from within that query, did it delete the rows from TableTwo, and NOT from TableOne as expected? I've just lost ~3 days of work.
Edit: For clarity, I manually selected the rows in the query window and deleted them. I did not use a delete query - I've been stung by that a couple of times lately.
Since you have deleted the records manually, your query has to be updateable. This means that your query couldn't have been solely a cartesian join or a join without referential integrity, since these queries are non-updateable in ms access.
When I recreate your query based on two fields without indexes or primary keys, I am not even able to manualy delete records. This leads me to believe there was unknowingly a relationship established which deleted the records in table two. Perhaps you should take a look in the design view of your queries and relationships window, since the query itself should indeed select only records from table one.
Not sure why it got deleted, but I suggest to rewrite your query:
delete TableOne
where LINK in (select LINK from TableTwo)
This should work for you:
DELETE TableOne
FROM TableOne a
INNER JOIN
TableTwo b on b.Bid = a.Bid
and [my filter condition]
I'm not a SQL expert (by any means). I know I can do this programatically in vb.net (which I will if I can't figure out how to do it with an SQL statement).
I need to copy the value of a field in one table to another field in a separate table where a specific condition is true. I've tried my best to model it below:
Table1.field1
Table1.field2
Table2.field1
Table2.field2
I want to copy the value
from :Table2.field2
To :Table1.field2
where Table1.field1 = Table2.field1 (There are about 3000 rows).
Basically I have some string information in one field for a whole bunch of records where I need to copy that to the same records but in a different field in a different table. Does that make sense?
I know I'm supposed to provide some code to show I'm trying; however, I really don't know where to even start. I'm willing to tough it out on my own if maybe someone can point me in the right direction? I'd appreciate any help/guidance.
Thanks!
With SQL Server, you can UPDATE a table using a join:
UPDATE t1
SET t1.field2 = t2.field2
FROM table1 t1
JOIN table2 t2
ON t1.field1 = t2.field1
I have two different tables with similar schema in different database. What is the best way to compare records between these two tables. I need to find out-
records that exists in first table whose corresponding record does not exist in second table filtering records from the first table with some where clauses.
So far I have come with this SQL construct:
Select t1_col1, t1_ col2 from table1
where t1_col1=<condition> AND
t1_col2=<> AND
NOT EXISTS
(SELECT * FROM
table2
WHERE
t1_col1=t2_col1 AND
t1_col2=t2_col2)
Is there a better way to do this?
This above query seems fine but I suspect it is doing row by row comparison without evaluating the conditions in the first part of the query because the first part of the query will reduce the resultset very much. Is this happening?
Just use except keyword!!!
Select t1_col1, t1_ col2 from table1
where t1_col1=<condition> AND
t1_col2=<condition>
except
SELECT t2_col1, t2_ col2 FROM table2
It returns any distinct values from the query to the left of the EXCEPT operand that are not also returned from the right query.
For more information on MSDN
If the data in both table are expected to have the same primary key, you can use IN keyword to filter those are not found in the other table. This could be the simplest way.
If you are open to third party tools like Redgate Data Compare you can try it, it's a very nice tool. Visual Studio 2010 Ultimate edition also have this feature.
I want to run this DELETE query:
DELETE * FROM Table1 WHERE Table1.ID <> (SELECT Table1.ID FROM Table1 WHERE ....)
The query in brackets returns all the IDs I want to keep in Table1 (This query works on it's own, I tested it). But as soon as I add the DELETE part I get the following error: "At most one record can be returned by this subquery". I tried the Code
DELETE * FROM Table1 WHERE Table1.ID NOT IN (SELECT Table1.ID FROM Table1 WHERE ....)
But now my database hangs and doesn't do anything anymore...
Thank you for your help!
Actually * is not necessary for delete statements because it deletes the entire row that matches the where condition.
Generally <> (Not equal to) is used to provide a single static value. (like below)
DELETE FROM Table1 WHERE Table1.ID <> 1
But the subquery returns rows/records (with the selected columns). Hence you got the error: At most one record can be returned by this subquery
Coming to the NOT IN clause that you are using, it is the right way to do it, but NOT IN can become pretty complex if more number of rows are involved in the subquery as NOT IN does a join behind the hood.
The best way in your case is to use NOT(condition) as you already know the condition for which you need the required table IDs. (like below)
DELETE FROM Table1 WHERE NOT(condition)
This does your job pretty fast as there are no joins involved like in the earlier case.