In my SQL Server 2008 I've got two tables.
Table: All kinds of Users with unique ID's
Table: Blacklisted Users with ID's
Now I'd like to get all Users that are not on the blacklist.
Just doesn't work like I want it to
SELECT A.ID, B.ID FROM Users AS A INNER JOIN Blacklist AS B ON
A.ID != B.ID
Can someone help?
If you expect it to not to be in Blacklist, you won't have any data to select from blacklist in select statement
SELECT A.*
FROM Users A
Where A.ID NOT IN (Select Id From Blacklist )
If you wish, read more about Subqueries with NOT IN
What you want is an anti-join, something like this:
SELECT A.ID, B.ID FROM Users AS A LEFT JOIN Blacklist AS B ON
A.ID = B.ID
WHERE B.ID IS NULL
That is, we perform the join, and then in the WHERE clause we apply a filter which eliminates rows where the join was successful.
Your original query doesn't work (assuming that there is more than one row in Blacklist and that they have different ID values) because, for any ID value in A, we can find a row in B which doesn't match it - even if there's also a row which does match it.
SELECT *
From Users
WHERE ID NOT IN (SELECT ID From BlackListedUsers)
That should select all that are not in the blacklist table.
Related
I face issue about duplicate data when join table, here my sample data table I have
-- Table A
I want to join with
-- Table B
this my query notation for join both table,
select a.trans_id, name
from tableA a
inner join tableB b
on a.ID_Trans = b.trans_id
and this the result, why I get the duplicating data which should show only two lines of data, please help me to solve this case.
Firstly, as you have been told multiple times in the comments, this is working exactly as you have written, and (more importantly) as intended. You have 2 rows in tableA and those 2 rows match 2 rows in your table tableB according to the ON clause. This means that each join operation, for the each of the rows in tableA, results in 2 rows as well; thus 4 rows (2 * 2 = 4).
Considering that your table, TableA only has one column then it seems that you should be cleaning up that data and deleting the duplicates. There are plenty of examples on how to do that already (example).
Perhaps the column you show us in TableA is one many, and thus instead you have a denormalisation issue, and instead there should be another table with the details of Id_trans and a PRIMARY KEY or UNIQUE CONSTRAINT/INDEX on it. Then you would join fron that table to TableB.
Finally, what you might be after is an EXISTS, which would look like this:
SELECT B.trans_id, B.[name]
FROM dbo.TableB B
WHERE EXISTS(SELECT 1
FROM dbo.TableA A
WHERE A.ID_Trans = B.trans_id); --Odd that it's called ID_Trans in one table, and Trans_ID in another
As the comments mentioned your query does exactly what you asked it to do but I think you wanted something like:
select a.trans_id, a.name, b.name
from tableA a
inner join tableB b on a.trans_id = b.trans_id
group by a.trans_id, a.name, b.name
Since there are two rows in both table with same ID join will make them four. You can use distinct to remove duplicates:
select distinct a.trans_id, name
from tableA a
inner join tableB b
on a.id_trans = b.trans_id
But I would suggest to use exists:
select trans_id, name
from tableB b
exists (select 1 from tableA a where a.trans_id=b.trans_id)
I'm trying to take the distinct IDs that appear in table a, filter table b for only these distinct IDs from table a, and present the remaining columns from b. I've tried:
SELECT * FROM
(
SELECT DISTINCT
a.ID,
a.test_group,
b.ch_name,
b.donation_amt
FROM table_a a
INNER JOIN table_b b
ON a.ID=b.ID
ORDER by a.ID;
) t
This doesn't seem to work. This query worked:
SELECT DISTINCT a.ID, a.test_group, b.ch_name, b.donation_amt
FROM table_a a
inner join table_b b
on a.ID = b.ID
order by a.ID
But I'm not entirely sure this is the correct way to go about it. Is this second query only going to take unique combinations of a.ID and a.test_group or does it know to only take distinct values of a.ID which is what I want.
Your first and second query are similar.(just that you can not use ; inside your query) Both will produce the same result.
Even your second query which you think is giving you desired output, can not produce the output what you actually want.
Distinct works on the entire column list of the select clause.
In your case, if for the same a.id there is different a.test_group available then it will have multiple records with same a.id and different a.test_group.
I need to write a stored procedures to update contacts who have no active pledges in our database, I can't seem to find a way of counting contacts with 0 rows on the pledges table.
The external key in the pledges table is supporter_id, I've tried using Count(*), but it only returns 1 or more.
Thanks in advance.
PS: This is on a MS SQL database.
We'd need more information to give you a specific answer, but there are a number of ways to identify non-matching records, here are two:
LEFT JOIN:
SELECT a.*
FROM TableA a
LEFT JOIN TableB b
ON a.ID = b.ID
WHERE b.ID IS NULL
NOT EXISTS:
SELECT *
FROM TableA a
WHERE NOT EXISTS (SELECT *
FROM TableB b
WHERE a.ID = b.ID)
I ended using a subquery so I first determine who has pledges of the type I want and then look for contacts who are not in that list.
thanks for the responses.
What should I do if I want to:
For now, there are table A and table B,
A:
id, name, address //the id is unique
B
id, contact, email
Since one person may have more than one contact and email, or have no contact and email(which means no record in table B)
Now I want to count how many records for each id, even 0:
And the result will look like:
id, name, contact_email_total_count
How can I do that(for now the only place I can not figure out is how to count 0 record since there is no record in table B)?
For that case you will want to use a LEFT JOIN, then add an aggregate and a GROUP BY:
select a.id,
a.name,
count(b.id) as contact_email_total_count
from tablea a
left join tableb b
on a.id = b.id
group by a.id, a.name
See SQL Fiddle with Demo
If you need help learning join syntax here is a great visual explanation of joins.
Based on your comment the typical order of execution is as follows:
FROM
ON
JOIN
WHERE
GROUP BY
HAVING
SELECT
ORDER BY
Need to do a left join to maintain the records in table A regardless of B:
PostgreSQL: left outer join syntax
Need to aggregate the count of records in B:
PostgreSQL GROUP BY different from MySQL?
Assume I have two data tables and a linking table as such:
A B A_B_Link
----- ----- -----
ID ID A_ID
Name Name B_ID
2 Questions:
I would like to write a query so that I have all of A's columns and a count of how many B's are linked to A, what is the best way to do this?
Is there a way to have a query return a row with all of the columns from A and a column containing all of linked names from B (maybe separated by some delimiter?)
Note that the query must return distinct rows from A, so a simple left outer join is not going to work here...I'm guessing I'll need nested select statements?
For your first question:
SELECT A.ID, A.Name, COUNT(ab.B_ID) AS bcount
FROM A LEFT JOIN A_B_Link ab ON (ab.A_ID = A.ID)
GROUP BY A.ID, A.Name;
This outputs one row per row of A, with the count of matching B's. Note that you must list all columns of A in the GROUP BY statement; there's no way to use a wildcard here.
An alternate solution is to use a correlated subquery, as #Ray Booysen shows:
SELECT A.*,
(SELECT COUNT(*) FROM A_B_Link
WHERE A_B_Link.A_ID = A.A_ID) AS bcount
FROM A;
This works, but correlated subqueries aren't very good for performance.
For your second question, you need something like MySQL's GROUP_CONCAT() aggregate function. In MySQL, you can get a comma-separated list of B.Name per row of A like this:
SELECT A.*, GROUP_CONCAT(B.Name) AS bname_list
FROM A
LEFT OUTER JOIN A_B_Link ab ON (A.ID = ab.A_ID)
LEFT OUTER JOIN B ON (ab.B_ID = B.ID)
GROUP BY A.ID;
There's no easy equivalent in Microsoft SQL Server. Check here for another question on SO about this:
"Simulating group_concat MySQL function in MS SQL Server 2005?"
Or Google for 'microsoft SQL server "group_concat"' for a variety of other solutions.
For #1
SELECT A.*,
(SELECT COUNT(*) FROM A_B_Link WHERE A_B_Link.A_ID = AOuter.A_ID)
FROM A as AOuter
SELECT A.*, COUNT(B_ID)
FROM A
LEFT JOIN A_B_Link ab ON ab.A_ID=A.ID