Simply, I want to find a solution for testing if one column value exits within another, or not, across tables. I've naturally jumped to 'NOT IN clause' but I've also discovered I can't use a colum name within the bracket (b.full_name)
SELECT
*
FROM
tbl1_name a
INNER JOIN
tbl2_name
ON a.id = b.id
WHERE
a.name NOT IN (b.full_name);
What clause can I use to achieve what I'm looking for etc.
You could simply do
SELECT * FROM tbl1_name a
INNER JOIN tbl2_name ON a.id = b.id
WHERE a.name <> b.full_name;
The IN keyword is normally used to check for multiple values example
NOT IN ('A', 'B');
Or
NOT IN (subquery);
You can use subquery after not in clause and select all the names from the table b. Hope it will resolve your problem.
Select * from table1 a inner join table2 b
on a.id=b.id
where a.name not in
(Select names from table2)
you can perform that using subqueries, this way :
SELECT * FROM tbl1_name a
WHERE a.name IN (SELECT b.full_name FROM tbl2_name b WHERE a.id = b.id);
Related
I have create a sql query that the sketch is like this
select *
from A
where A.id in (select B.id1, B.id2 from B);
where the main select returns those values for which A.id coincides with either B.id1 or B.id2.
Clearly this solution doesn't work as the cardinality doesn't match in the where clause. How can I overcome this problem?
One solution would be to make two sub-queries, one for B.id1 and one for B.id2, but as my sub-query is much longer than in this example I was looking for a more elegant solution.
I'm using Mysql
EDIT 1
As long as the syntax is simpler than using two sub-queries I have no issues using joins
EDIT 2
Thanks #NullSoulException. I tried the first solution and works as expected!!
Something like the below should do the trick.
select *
From table1 a , (select id1 , id2 from table2 ) b
where (a.id = b.id1) or (a.id = b.id2)
or you can JOIN with the same table twice by giving the joined tables an alias.
select * from table1 a
INNER JOIN table2 b1 on a.id = b1.id1
INNER JOIN table2 b2 on a.id = b2.id2
Please test the above against your datasets/tables..
I have 2 MySQL tables A and B.
I would like to select only the records from B where a certain value exists in A.
Example:
A has columns: aID, Name
B has columns: bID, aID, Name
I just want the records from B for which aID exists in A.
Many thanks.
You need to do either INNER JOIN - records that exists in both tables, or use LEFT join, to show records that exists in A and matching IDs exists in B
A good reference:
You need to make a join, and if you don't want to retrieve anything from table b, just return values from table a.
This should work
select b.* from b join a on b.aID=a.aID
Below query will also work and will be effective
SELECT * FROM B
WHERE B.aID IN (SELECT DISTINCT aID FROM A)
You just need a simple inner join between tables A and B. Since they are related on the aID column, you can use that to join them together:
SELECT b.*
FROM tableB b
JOIN tableA a ON a.aID = b.aID;
This will only select rows in which the aID value from tableB exists in tableA. If there is no connection, the rows can't be included in the join.
While I recommend using a join, you can also replace it with a subquery, like this:
SELECT *
FROM tableB
WHERE aID NOT IN (SELECT aID FROM tableA)
You can use join like this.
Select b.col1,b.col2... From tableB b inner join table tableA a on b.field = a.field
Have you tried using a LEFT JOIN?
SELECT b.* FROM tableB b LEFT JOIN tableA a ON b.aID = a.aID
I'm trying to improve a (not so much) simple query:
I need to retrieve every row from Table A.
Then join Table A with Table B so I get all the data I need.
At the same time, I need to add an extra column with the count() from Table C.
Something like:
SELECT a.*,
(SELECT Count(*)
FROM table_c c
WHERE c.a_id = a.id) AS counter,
b.*
FROM table_a a
LEFT JOIN table_b b
ON b.a_id = a.id
This works, ok, but in reality, I'm just making 2 queries and I need to improve this so it only do one (if, its even possible).
Anyone knows how can I achive that?
The simplest approach is likely to just move the correlated sub-query into a sub-query.
NOTE: Many optimisers deal with correlated sub-queries extremely effectively. Your example query could be perfectly reasonable.
SELECT
a.*,
b.*,
c.row_count
FROM
table_a a
LEFT JOIN
table_b b
ON b.a_id = a.id
LEFT JOIN
(
SELECT
a_id,
Count(*) row_count
FROM
table_c
GROUP BY
a_id
)
c
ON c.a_id = a.id
Another Note: SQL is an expression, it is not executed directly, it is translated into a plan using nest loops, hash joins, etc. Do not assume that having two queries is a bad thing. In this case my example may significantly minimise the number of reads compared to a single query and then use of GROUP BY and COUNT(DISTINCT).
Try this:
SELECT
tmp.*,
SUM(IF(c.a_id IS NULL,0,1)) as counter,
FROM (
SELECT
a.id as aid,
b.id as bid,
a.*,
b.*
FROM
table_a a
LEFT JOIN table_b b
ON b.a_id = a.id
) as tmp
LEFT JOIN table_c c
ON c.a_id = tmp.id
GROUP BY
tmp.aid,
tmp.bid
I have 3 tables A,B and C. In the stored procedure,I have used a query to get the result but i also want the total number of records i got from the above query.
Is this possible. I tried using something like this
Select count(*)
from (
select A.Name,B.Address,C.grade
from A,B,C
where A.id=B.id
AND B.Tlno=C.tlno
)
But this is not working.
(1) stop using old-style x,y,z joins.
SELECT A.Name,B.Address,C.grade
FROM dbo.A
INNER JOIN dbo.B ON A.id = B.id
INNER JOIN dbo.C ON B.Tlno = C.tlno;
(2) you can add a count(*) over() to the entire resultset. This is kind of wasteful because it returns the count on every row:
SELECT A.Name, B.Address, C.grade, row_count = COUNT(*) OVER ()
FROM dbo.A
INNER JOIN dbo.B ON A.id = B.id
INNER JOIN dbo.C ON B.Tlno = C.tlno;
You can use a windowing function:
select A.Name,
B.Address,
C.grade,
count(*) over () as total_count
from A,B,C
where A.id=B.id
AND B.Tlno=C.tlno
this will return the total count in each and every row though (but it will be the same number for all rows).
Alternative would be to use the ##rowcount keyword:
SELECT A.Name, B.Address, C.grade, ##rowcount
FROM dbo.A
INNER JOIN dbo.B ON A.id = B.id
INNER JOIN dbo.C ON B.Tlno = C.tlno;
Same result as the windowing function though, so you get the total count on each row. I'm curious if there is a performance difference between the two... (don't have SHOWPLAN permission at my current client unfortunately)
use a table variable as below
declare #num table (accname varchar(200),subnet varchar(200))
insert into #num(accname,subnet) Select a.accountname,s.subnet from tbl_accounts a,tbl_accountsubnet s where a.accountid=s.accountid
select COUNT(*) from #num;
Im in a position where I cannot alter the table structure of my database and I have Ambiguous Column Names in [table1] and [table2]. I do not need to use any fields from [table2] but its existence is necessary to relate to another table. Is there a way that I handle this?
Every time you refer to one of the ambiguous column names you should specify the table name or alias.
SELECT ...
FROM [table1]
JOIN [table2]
ON [table1].ambiguous_column = [table2].ambiguous_column
AND ...
use table aliases
SELECT A.*
FROM TABLE_A A
JOIN TABLE_B B ON A.ID = B.ID
ORDER BY A.FIELD
use the SQL statement AS to create uniquel names
SELECT
A.feld1 AS F1,
A.feld2 AS F2,
B.feld1 AS F3
FROM table1 AS A
JOIN table2 AS B ON A.id = B.id
ORDER BY A.field1