One of my tables has a column named "t_name" which supplies an exact name (ie: Google)
And another table has two columns named
m_team_home and m_team_away
Both m_team_home and m_team_away would be INT's in the database but would grab the name from the first table. My joined query is only able to grab the home's team name, and I don't know how to get the away team's name because it will output the same thing.
I know it may be hard to explain, but much help would be appreciated.
sounds like you want to join on the table twice
SELECT a.team, a1.team
FROM table t
JOIN another_table a on a.m_team_home = t.id -- t.id or whatever is in that table that maps to the home / away teams
JOIN another_table a1 on a1.m_team_away = t.id
that way you can get the name for the home team and away team.. you may want to consider making those LEFT joins just incase one doesn't exist and it gets filtered out
Related
I have 2 tables. One (domains) has domain ids, and domain names (dom_id, dom_url).
the other contains actual data, 2 of which columns require a TO and FROM domain names. So I have 2 columns rev_dom_from and rev_dom_for, both of which store the domain name id, from the domains table.
Simple.
Now I need to actually display both domain names on the webpage. I know how to display one or the other, via the LEFT JOIN domains ON reviews.rev_dom_for = domains.dom_url query, and then you echo out the dom_url, which would echo out the domain name in the rev_dom_for column.
But how would I make it echo out the 2nd domain name, in the dom_rev_from column?
you'd use another join, something along these lines:
SELECT toD.dom_url AS ToURL,
fromD.dom_url AS FromUrl,
rvw.*
FROM reviews AS rvw
LEFT JOIN domain AS toD
ON toD.Dom_ID = rvw.rev_dom_for
LEFT JOIN domain AS fromD
ON fromD.Dom_ID = rvw.rev_dom_from
EDIT:
All you're doing is joining in the table multiple times. Look at the query in the post: it selects the values from the Reviews tables (aliased as rvw), that table provides you 2 references to the Domain table (a FOR and a FROM).
At this point it's a simple matter to left join the Domain table to the Reviews table. Once (aliased as toD) for the FOR, and a second time (aliased as fromD) for the FROM.
Then in the SELECT list, you will select the DOM_URL fields from both LEFT JOINS of the DOMAIN table, referencing them by the table alias for each joined in reference to the Domains table, and alias them as the ToURL and FromUrl.
For more info about aliasing in SQL, read here.
Given the following tables..
Domain Table
dom_id | dom_url
Review Table
rev_id | rev_dom_from | rev_dom_for
Try this sql... (It's pretty much the same thing that Stephen Wrighton wrote above)
The trick is that you are basically selecting from the domain table twice in the same query and joining the results.
Select d1.dom_url, d2.dom_id from
review r, domain d1, domain d2
where d1.dom_id = r.rev_dom_from
and d2.dom_id = r.rev_dom_for
If you are still stuck, please be more specific with exactly it is that you don't understand.
Read this and try, this will help you:
Table1
column11,column12,column13,column14
Table2
column21,column22,column23,column24
SELECT table1.column11,table1.column12,table2asnew1.column21,table2asnew2.column21
FROM table1 INNER JOIN table2 AS table2asnew1 ON table1.column11=table2asnew1.column21 INNER TABLE table2 as table2asnew2 ON table1.column12=table2asnew2.column22
table2asnew1 is an instance of table 2 which is matched by table1.column11=table2asnew1.column21
and
table2asnew2 is another instance of table 2 which is matched by table1.column12=table2asnew2.column22
How can i use in table field values in the url
SQL Query wherein all 3 tables are joined
select * from nfojm_usedcar_variants cv
inner join nfojm_usedcar_products cp
inner join nfojm_usedcar_categories cc on
cc.id=cp.prod_cat_id and
cp.id=cv.v_prod_id and
cv.state='1' order by cv.id desc
Output as checked
Then it combines all 3 tables
nfojm_usedcar_variants
nfojm_usedcar_products
nfojm_usedcar_categories
However - all 3 tables have unique field i.e id (but with different values)
I need to pass on value of id and v_prod_id in a url
say url been :-
<a href="index.php?option=com_usedcar&pid='.$row->v_prod_id.'&vid='.$row->id.'">
But id been common field in most of the tables hence its not picking in correctly from nfojm_usedcar_variants,
Can some one help to modify a function so as to fetch in value of id and v_prod_id from the respective table of nfojm_usedcar_variants
thanks
If you have multiple tables in a join that share a common column name, and you need them, then alias them. Such as:
select a.id as aid,a.theName,b.id as bid,b.year
from tableA a
join tableB b
on b.id=a.id
then refer to those columns as aid and bid in your code that follows.
Try to avoid Ever doing a select *. Be explicit. You never know what comes flying out of a select * typically. And odds are you don't need it all. Select * is fine for messing around, but not for production code. And you can't control common column names with select *. We like to control things afterall, no?
I'm currently having a problem with a legacy app I just inherited on my new job. I have a SQL query that's way too long to respond and I need to find a way to fasten it.
This query acts on 3 tables:
SESSION contains all users visits
CONTACT contains all the messages people have been sending through a form and contains a "session_id" field that links back to the SESSION id field
ACCOUNT contains users accounts (people who registered on the website) and whose "id" field is linked back in SESSION (through a "SESSION.account_id" field). ACCOUNT and CONTACT are no linked in any way, besides the SESSION table (legacy app...).
I can't change this structure unfortunately.
My query tries to recover ALL the interesting sessions to serve to the administrator. I need to find all sessions that links back to an account OR a contact form.
Currently, the query is structured like that :
SELECT s.id
/* a few fields from ACCOUNT and CONTACT tables */
FROM session s
LEFT JOIN account act ON act.id = s.account_id
LEFT JOIN contact c on c.session_id = s.id
WHERE s.programme_id = :program_id
AND (
c.id IS NOT NULL
OR
act.id IS NOT NULL
)
Problem is, the SESSION table is growing pretty fast (as you can expect) and with 400k records it slows things down for some programs ( :programme_id in the query).
I tried to use an UNION query with two INNER JOIN query, one between SESSION and ACCOUNT and the other one between SESSION and CONTACT, but it doesn't give me the same number of records and I don't really understand why.
Can somebody help me to find a better way to make this query ?
Thanks a lot in advance.
I think you just need indexes. For this query:
SELECT s.id
/* a few fields from ACCOUNT and CONTACT tables */
FROM session s LEFT JOIN
account act
ON act.id = s.account_id LEFT JOIN
contact c
ON c.session_id = s.id
WHERE s.programme_id = :program_id AND
(c.id IS NOT NULL OR act.id IS NOT NULL);
You want indexes on session(programme_id, account_id, id), account(id) and contact(session_id).
It is important that programme_id be the first column in the index on session.
#Gordon already suggested you add an index, which is generally the easy and effective solution, so I'm going to answer a different part of your question.
I tried to use an UNION query with two INNER JOIN query, one between
SESSION and ACCOUNT and the other one between SESSION and CONTACT, but
it doesn't give me the same number of records and I don't really
understand why.
That part is rather simple: the JOIN returns a result set that contains the rows of both tables joined together. So in the first case you would end up with a result that looks like
session.id, session.column2, session.column3, ..., account.id, account.column2, account.column3, ....
and a second where
session.id, session.column2, session.column3, ..., contact.id, contact.column2, contact.column3, ....
Then an UNION will faill unless the contact and account tables have the same number of columns with correspoding types, which is unlikely. Otherwise, the database will be unable to perform a UNION. From the docs (emphasis mine):
The column names from the first SELECT statement are used as the column names for the results returned. Selected columns listed in corresponding positions of each SELECT statement should have the same data type. (For example, the first column selected by the first statement should have the same type as the first column selected by the other statements.)
Just perform both INNER JOINs seperately and compare the results if you're unsure.
If you want to stick to an UNION solution, make sure to perform a SELECT only on corresponding columns : doing SELECT s.id would be trivial but it should work, for instance.
MySQL setup: step by step.
programs -> linked to --> speakers (by program_id)
At this point, it's easy for me to query all the data:
SELECT *
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
Nice and easy.
The trick for me is this. My speakers table is also linked to a third table, "books." So in the "speakers" table, I have "book_id" and in the "books" table, the book_id is linked to a name.
I've tried this (including a WHERE you'll notice):
SELECT *
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
LIMIT 5
No results.
My questions:
What am I doing wrong?
What's the most efficient way to make this query?
Basically, I want to get back all the programs data and the books data, but instead of the book_id, I need it to come back as the book name (from the 3rd table).
Thanks in advance for your help.
UPDATE:
(rather than opening a brand new question)
The left join worked for me. However, I have a new problem. Multiple books can be assigned to a single speaker.
Using the left join, returns two rows!! What do I need to add to return only a single row, but separate the two books.
is there any chance that the books table doesn't have any matching columns for speakers.book_id?
Try using a left join which will still return the program/speaker combinations, even if there are no matches in books.
SELECT *
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
LEFT JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
LIMIT 5
Btw, could you post the table schemas for all tables involved, and exactly what output (or reasonable representation) you'd expect to get?
Edit: Response to op author comment
you can use group by and group_concat to put all the books on one row.
e.g.
SELECT speakers.speaker_id,
speakers.speaker_name,
programs.program_id,
programs.program_name,
group_concat(books.book_name)
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
LEFT JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
GROUP BY speakers.id
LIMIT 5
Note: since I don't know the exact column names, these may be off
That's typically efficient. There is some kind of assumption you are making that isn't true. Do your speakers have books assigned? If they don't that last JOIN should be a LEFT JOIN.
This kind of query is typically pretty efficient, since you almost certainly have primary keys as indexes. The main issue would be whether your indexes are covering (which is more likely to occur if you don't use SELECT *, but instead select only the columns you need).
I have 2 tables. One (domains) has domain ids, and domain names (dom_id, dom_url).
the other contains actual data, 2 of which columns require a TO and FROM domain names. So I have 2 columns rev_dom_from and rev_dom_for, both of which store the domain name id, from the domains table.
Simple.
Now I need to actually display both domain names on the webpage. I know how to display one or the other, via the LEFT JOIN domains ON reviews.rev_dom_for = domains.dom_url query, and then you echo out the dom_url, which would echo out the domain name in the rev_dom_for column.
But how would I make it echo out the 2nd domain name, in the dom_rev_from column?
you'd use another join, something along these lines:
SELECT toD.dom_url AS ToURL,
fromD.dom_url AS FromUrl,
rvw.*
FROM reviews AS rvw
LEFT JOIN domain AS toD
ON toD.Dom_ID = rvw.rev_dom_for
LEFT JOIN domain AS fromD
ON fromD.Dom_ID = rvw.rev_dom_from
EDIT:
All you're doing is joining in the table multiple times. Look at the query in the post: it selects the values from the Reviews tables (aliased as rvw), that table provides you 2 references to the Domain table (a FOR and a FROM).
At this point it's a simple matter to left join the Domain table to the Reviews table. Once (aliased as toD) for the FOR, and a second time (aliased as fromD) for the FROM.
Then in the SELECT list, you will select the DOM_URL fields from both LEFT JOINS of the DOMAIN table, referencing them by the table alias for each joined in reference to the Domains table, and alias them as the ToURL and FromUrl.
For more info about aliasing in SQL, read here.
Given the following tables..
Domain Table
dom_id | dom_url
Review Table
rev_id | rev_dom_from | rev_dom_for
Try this sql... (It's pretty much the same thing that Stephen Wrighton wrote above)
The trick is that you are basically selecting from the domain table twice in the same query and joining the results.
Select d1.dom_url, d2.dom_id from
review r, domain d1, domain d2
where d1.dom_id = r.rev_dom_from
and d2.dom_id = r.rev_dom_for
If you are still stuck, please be more specific with exactly it is that you don't understand.
Read this and try, this will help you:
Table1
column11,column12,column13,column14
Table2
column21,column22,column23,column24
SELECT table1.column11,table1.column12,table2asnew1.column21,table2asnew2.column21
FROM table1 INNER JOIN table2 AS table2asnew1 ON table1.column11=table2asnew1.column21 INNER TABLE table2 as table2asnew2 ON table1.column12=table2asnew2.column22
table2asnew1 is an instance of table 2 which is matched by table1.column11=table2asnew1.column21
and
table2asnew2 is another instance of table 2 which is matched by table1.column12=table2asnew2.column22