Table a:
userid | text
9 | Lorem ipsum do...
Table b:
id | status
9 | 1
Question:
I want to select * from table a where table b under connection from uid -> where the id status=1 is. I don't know if it's possible.
I searched about it, but I've found nothing.
My Query:
SELECT * FROM tablea a WHERE id IN (SELECT id FROM tableb b WHERE b.status='1' AND b.id = a.userid)
inner join
select *
from a inner join b on a.userid = b.id
where b.status = 1;
left join
select *
from a left join b on a.userid = b.id
where b.status = 1;
or
right join
select *
from a right join b on a.userid = b.id
where b.status = 1;
see demo here: SqlFiddle
Check the sqlfiddle to see the difference, it is more if you expect that id exists in table-a or not, where it exists in table-b with status=1.
If you skip the b.status then you might need to go for the inner join query.
Please study the different query to learn about joins, go to the sqlfiddle and remove the b.status condition to see the results.
Take a look at join image below and learn the difference with easy illustration...
Related
I have to get A.Ref_id, B.Ref_id and B_Id's Ref_id
Table A_B having Column_A_ID and Column_B_ID
Table A having ID, Ref_id, Name, B_Id (This is the B.ID from table B)
Table B having ID, Ref_id, Name
Currently I'm having the following query
SELECT A.Ref_id as A_Ref_Id, B.Ref_id as B_Ref_Id, B_Id
FROM A_B
JOIN A on A_B.Column_A_ID = A.Id
JOIN B on A_B.Column_B_ID = B.Id
JOIN B AS Main_B on B.id = A.B_id;
By this query I'm getting the A.Ref_Id and B.Ref_Id columns correctly as they are showing their relevant Ref_id but for B_Id I want to have the Ref_id and it is showing the B.id instead.
You want this (right?): The value of B.Ref_id in the row where B.ID = A.B_Id while this row in turn must have A.ID=A_B.Column_A_ID. And the whole thing for every row in A_B:
SELECT A.Ref_id as A_Ref_id, B.Ref_id as B_Ref_id, Main_B.Ref_id
FROM A_B
JOIN A ON A_B.Column_A_ID = A.Id
JOIN B ON A_B.Column_B_ID = B.Id
JOIN B AS Main_B on Main_B.id = A.B_id;
(Last line of code with the important correction which was proposed by #Mojtaba)
So far, I see the ON condition of the last join has to use the alias name of table B:
SELECT A.Ref_id as A_Ref_Id, B.Ref_id as B_Ref_Id, B_Id
FROM A_B
JOIN A on A_B.Column_A_ID = A.Id
JOIN B on A_B.Column_B_ID = B.Id
JOIN B AS Main_B on Main_B.id = A.B_id;
By the way, having some example in sqlFiddle could be more helpful
I have two database tables with "one to many" relationship
let say, table A and Table B
One field from Table A is a foreign key in table B
I wanna fetch just one record from table A as well as table B (given table A's primary key)
table A
id name
--------------------
1 ABC
2 XYZ
Table B
id A_id email
------------------------------------------------
1 1 temp#temp1.com
2 1 temp#temp2.com
3 1 temp#temp3.com
4 2 temp#temp4.com
4 2 temp#temp5.com
Answer should be like this (Single Record From Table B)
For a.id = 1
A.id, A.name,B.email
-------------------------
1, ABC, temp#temp1.com
For a.id = 2
A.id, A.name,B.email
-------------------------
1, XYZ, temp#temp4.com
I used this query, but it returns all the records from table B(as table B has multiple records for each record in Table A)
SELECT a.id,a.name, b.email FROM A a, B b WHERE a.id = 1 AND b.A_id = a.id
I have created a SQL Fiddle for the demo here: http://www.sqlfiddle.com/#!2/15ae7/5
The query that you can use for getting the desired output is:
SELECT
tableA.id,
tableA.name,
tableB.email
FROM tableA
LEFT OUTER JOIN tableB ON tableB.A_id = tableA.id
GROUP BY tableB.A_id;
For more information on JOINS and GROUP BY you can refer to the following pages:
http://dev.mysql.com/doc/refman/5.0/en/join.html
https://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html
Try a JOIN
SELECT
a.id,
a.name,
b.email
FROM A a
LEFT JOIN B b ON b.A_id = a.id
WHERE a.id = 1;
GROUP BY b.A_id
More info on JOINS
You can use LIMIT if you want only one record.
SELECT a.id,a.name, b.email FROM A a, B b WHERE a.id = 1 AND b.A_id = a.id LIMIT 0,1
Hope this helps you.
I need to get both table and here is the table structure
Table A
UserID
Username
Status
IntroCode
Table B
IntroCode
UserID
I want to get the table a data and join with table b on tblA.IntroCode = tblB.IntroCode, then get the username of tblB.userID. How can i do such join ?
I tried half way and stuck in the middle, please help. Thanks for reply
This is just a simple join.
SELECT a.*, b.* -- select your desired columns here
FROM tableA a
INNER JOIN tableB b
ON a.IntroCode = b.IntroCode
WHERE b.userid = valueHere
UPDATE 1
SELECT a.UserID,
a.`Username` OrigUserName,
a.`Status`,
c.`Username` IntroUserName
FROM tableA a
INNER JOIN tableB b
ON a.IntroCode = b.IntroCode
INNER JOIN tableA c
ON b.userID = c.userID
-- WHERE b.UserID = valueHere -- extra condition here
SELECT column_name(s)
FROM TableA
LEFT JOIN TableB
ON TableA.UserID=TableB.UserID
SELECT B.userID from TableA A
LEFT JOIN TableB B on A.IntroCode=B.IntroCode
select a.*,b.IntroCode from TableA a left join TableB b
on a.IntroCode = b.IntroCode
you have to give the columns with same name an unique value:
SELECT a.UserID as uid_a, b.UserID as uid_b
FROM tableA a
INNER JOIN tableB b ON a.IntroCode = b.IntroCode
WHERE b.UserID = 1
Use this query.
SELECT TableA.Username FROM TableA JOIN TableB ON (TableA.IntroCode = TableB.IntroCode);
use this query
SELECT * FROM tblA INNER JOIN tblB ON tblA.IntroCode = tblB.IntroCode where tblB.userid = value
I have this database design:
**users_tbl**
id
username
name
**posts_tbl**
id
url
users_id *FK REFERENCE to users table*
**posts_contents_tbl**
id
posts_id *FK REFERENCE to posts table
title
description
date
views
click
isDeleted
I'm using this query
SELECT a.name,a.username,c.*
FROM users_tbl a
LEFT JOIN posts_tbl b ON a.id = b.users_id
LEFT JOIN posts_contents_tbl c ON b.id = c.posts_id
ORDER BY c.id ASC
Why I try to run this query it gives me NULL results, sample output is like this
But when I try to remove the ORDER BY c.id ASC it gives me this output:
That's not my expected result.
My expected result would be it will display the posts_contents_tbl in Ascending order at the same time it won't show some null values. Some users in my database doesn't have posts data in the posts_tbl so they should not show too.
How would I do that one? Your help would be greatly appreciated and rewarded!
Thanks!
PS: I already have thousands record in my database.
In that case, you have to use INNER JOIN instead of LEFT JOIN because you only want users with posts to show. The reason why there are Null values is because the records are based on table users_tbl and you've mentioned that some of them have no post. Right?
Try this:
SELECT a.name,
a.username,
c.*
FROM users_tbl a
INNER JOIN posts_tbl b
ON a.id = b.users_id
INNER JOIN posts_contents_tbl c
ON b.id = c.posts_id
ORDER BY c.`date` DESC
I think this is what you are looking for:
SELECT a.name,a.username,c.*
FROM users_tbl a
INNER JOIN posts_tbl b
ON a.id = b.users_id
LEFT JOIN posts_contents_tbl c
ON b.id = c.posts_id
ORDER BY IFNULL(c.id, 0) ASC;
If you really needs that posts_tbl data should not display if not available.And all data of posts_contents_tbl then you need a RIGHT JOIN and INNER JOIN .
The Query like :-
SELECT a.name,a.username,c.*
FROM users_tbl a
INNER JOIN posts_tbl b ON a.id = b.users_id
RIGHT JOIN posts_contents_tbl c ON b.id = c.posts_id
ORDER BY c.id ASC;
I am trying to unify a pair of queries with a LEFT JOIN, so that I can perform an ORDER BY on a desired column.
Table A has an exclusive one-to-many relationship with Table B, and table B has an exclusive one-to-many relationship with Table C.
I want to get the maximum value of a column in Table C, for each row in Table A.
what I used to have was:
$tableA = SELECT * FROM tableA;
for each row in $tableA {
$maxValue = SELECT MAX(value) FROM tableC WHERE tableB_id IN (SELECT tableB_id FROM tableB WHERE tableA_id={$row['tableA_id']}) GROUP BY tableB_id;
}
and now I'm thinking along the lines of:
SELECT * FROM tableA LEFT JOIN (SELECT tableA_id, MAX(max_c_value) FROM (SELECT tableB_id, MAX(value) max_c_value FROM tableC GROUP BY tableB_id) t GROUP BY tableA_id) USING(tableA_id)
but I know that's gibberish. I am not sure where to go from here.
I'm finding it hard to explain the problem, sorry.
SELECT A.ID, MAX(C.MyField) as CField
FROM A
LEFT OUTER JOIN B
ON A.ID = B.A_ID
LEFT OUTER JOIN C
ON B.ID = C.B_ID
GROUP BY A.ID
You will get null value for CField if there is no rows corresponding.
select max(table3.field),table1.field from table1
join table2 on table1.id=table2.table1_id
join table3 on table2.id = table3.table2_id
group by table1.field
You were closer on the first try I think. You want something like this:
SELECT MAX(tableC.cValue) FROM tableA
LEFT JOIN tableB
ON tableA.tableA_id = tableB.tableA_id
LEFT JOIN tableC
ON tableB.tableB_id = tableC.tableB_id
http://www.w3schools.com/sql/sql_join.asp
I have managed to solve it on my own, only to come back here and find I was making things far too complicated for myself, getting lost in a sea of tables!
This code did actually work, but I have already replaced it with the simpler code suggested above:
SELECT * FROM A LEFT JOIN (
SELECT A_ID, MAX(val) FROM (
SELECT * FROM B LEFT JOIN (
SELECT B_ID, MAX(val) val FROM C GROUP BY B_ID
) x USING(B_ID)
) y GROUP BY A_ID
) z USING(A_ID);