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mysql extra columns with same name from two tables
(3 answers)
Closed 8 years ago.
I'm not even sure how exactly to ask this question so bear with me.
I have two tables, meets and locations, they are linked by the meet's 'loc' and the location's 'id'
I'm using this query:
$query = "SELECT * FROM meets LEFT JOIN locations ON locations.id=meets.loc ORDER BY date DESC";
$meets = mysqli_query($con, $query);
though it joins the table successfully I lose the meet's 'id' because it's being overwritten by the location's 'id'. So I end up with two identical entries 'id' and 'loc'.
Is there any way to avoid this because I need to call on the meet id?
do not select *, select the columns you need and rename them using the as key word like so
SELECT locations.id as loc_id, meets.id as meets_id, ... FROM meets LEFT JOIN locations ON locations.id=meets.loc ORDER BY date DESC
replacing ... with other columns you would like to select and possible renames of them.
You could alias the locations.id with a query like:
SELECT meets.*, locations.id AS loc_id FROM meets LEFT JOIN locations ON locations.id=meets.loc ORDER BY date DESC
You could add any other columns from locations that you might also need. You could further only select explicit columns from meet rather than meet.*
you could try to use SELECT meets.*, locations.id as locationId, locations.<row> as location<Row>, ...
Not sure if the syntax is exactly the same, but in SQL Server the syntax would be:
SELECT m.*, l.id as LocationId
FROM meets m
LEFT JOIN locations l
ON l.id=m.loc
ORDER BY date DESC
Related
NOTE: Just a practice problem.. NOT looking for free homework answers.
The practice problem I have asks to report the number of flights by plane’s year in ascending order of plane’s year. This requires the joining of two tables, the flights table and planes table. I believe the SQL should be relatively simple, and I think the main issue with mine is the vague select statement I currently have. I have looked at the different join methods, both explicit and implicit, and have also tried a left join with no luck.
If more table information is needed, I can share. The column the two tables share is year.
Also, very new here, so if there is something undesirable or incorrect about this post, please let me know.
select *,
count(*) as n_flights
from flights, planes
where flights.year = planes.year
order by planes.year asc
;
The output I am looking for:
The output I get:
Presumably, there is a column in the flights table that refers to the primary key of the planes table - let me assume plane_id: this is what you would use to join the tables.
Then, you want to aggregate by plane year, using a group by clause, and count the number of rows in each group:
select p.year, count(*) as n_flights
from flights f
inner join planes p on p.plane_id = f.plane_id
group by p.year
order by p.year
select planes.year, count(*)
from flights, planes
where flights.year = planes.year
group by planes.year
order by planes.year asc
I need to write a query to join 3 tables.
My tables are:
ucommerce_customer
ucommerce_order
ucommerce_order_line
All 3 tables have a column called order_id.
The table ucommerce_order has a column called order_status.
When the order_status is set to "open" I want to display the order details.
ResultSet myRs = myStmt.executeQuery
("SELECT * FROM ucommerce_customer
INNER JOIN ucommerce_order
INNER JOIN ucommerce_order_line
WHERE ucommerce_order.order_status = 'open'");
My query ignores the order status and displays all orders, open and closed.
Also I have several products so ucommerce_order_line has several entries for the same order_id, my query displays duplicate entries and it duplicates the entire list as well.
How can I write a query that will show only open orders without duplicating everything?
In MySQL, the on/using clause is optional. This is very sad because someone can make mistakes like you did. Your question only mentions one column, so perhaps that is all that is needed for the join:
SELECT *
FROM ucommerce_customer INNER JOIN
ucommerce_order
USING (orderId) INNER JOIN
ucommerce_order_line
USING (OrderId)
WHERE ucommerce_order.order_status = 'open';
I would be surprised if the customer table really had a column called OrderId (seems like a bad idea in most situations), so the first USING clause might want to use CustomerId.
I would recommend to use a natural join instead. Maybe that's where the errors are coming from.
The duplicates can be removed by running SELECT DISTINCT * ...
A categories table which contains id, category_name,category_type etc.
I am getting all the records with SELECT query.
suppose I have a category name Shared article and I want to get it first position in my records.
of course I am using simple query
SELECT `category_name`,`category_type`,`categories`.`id`,
count(`user_bookmarks`.`id`) as counter FROM `categories`
LEFT JOIN `user_bookmarks`
ON `categories`.`id`=`user_bookmarks`.`category_id`
WHERE `categories`.`user_id`=39 GROUP By `categories`.`category_name`
but I don't know how achieve my task?
Is it possible with MySQL?
Yes you can do as
order by
`categories`.`category_name` = 'Shared article' desc
EDIT. I missed the one main issue I was having. I want to display all the unique 'device_MAC' rows. So I want this query to output 3 rows (as per the original query). The issue I am having is connecting the data table to the remote_node table via dt_short = rn_short where the maximum timestamp for dt_short in the data table.
I am having trouble running a query on 3 tables (2 have many to many relations).
What I am trying to do:
Get each distinct rn_IEEE from the remotenodes table with the maximum timestamp (in the example this will get 3 rows with 3 distinct short addresses rn_short)
Join with the devicenames table on device_IEEE
Get each distinct dt_short from the data table with the maximum timestamp
Join dt_short with rn_short from the query above
Now the problem I am running into is that I can do the queries for the above individually, I have even gotten the first 3 of them together into a query but I cannot seem to properly join the last bit of data to get the result that I want.
I have been going in circles trying to solve this. Here is a link to SQL Fiddle which contains all the test data and the query as far as I got it, it does what i want for the first line but from table 'data' after the first line is NULL:
See this SQL fiddle
After going through your requirements and the data, it looks like you just need to change your query to include an INNER JOIN on the data table instead of a LEFT JOIN
See SQL Fiddle with Demo
select rn.*, dn.*, d.*
from remotenodes rn
inner join devicenames dn
on rn.rn_IEEE = dn.device_IEEE
and rn.rn_timestamp = (SELECT MAX(rn_timestamp) FROM remotenodes
WHERE rn.rn_IEEE = rn_IEEE
GROUP BY rn_IEEE)
inner join data d
on rn.rn_short = d.dt_short
AND d.dt_timestamp = (SELECT MAX(d2.dt_timestamp) AS ts
FROM data d2
WHERE d.dt_short = d2.dt_short
GROUP BY d2.dt_short)
what you have done the query in your SQL fiddle is right.Instead of using left join use inner join so that it will give you the first row
cheers.
Thanks for all your answers everyone. I managed to solve the problem by using views.
It's not the most efficient way but I think it will do for now.
Here is the SQL Fiddle link:
http://sqlfiddle.com/#!2/4076e/8
Try this query, for me its returning one row:
SELECT rn_short, rn_IEEE, device_name
FROM
(SELECT DISTINCTROW dt_short FROM (SELECT * FROM `data` ORDER BY `dt_timestamp` DESC) as data ) as a
JOIN
(SELECT rn_IEEE, rn_short, device_name FROM devicenames dn JOIN (SELECT DISTINCTROW rn_IEEE, rn_short FROM (SELECT * FROM `remotenodes` ORDER BY `rn_timestamp` DESC) as remotenodes GROUP BY rn_IEEE) as rn ON dn.device_IEEE = rn.rn_IEEE) as b
ON a.dt_short = b.rn_short
I need to gather posts from two mysql tables that have different columns and provide a WHERE clause to each set of tables. I appreciate the help, thanks in advance.
This is what I have tried...
SELECT
blabbing.id,
blabbing.mem_id,
blabbing.the_blab,
blabbing.blab_date,
blabbing.blab_type,
blabbing.device,
blabbing.fromid,
team_blabbing.team_id
FROM
blabbing
LEFT OUTER JOIN
team_blabbing
ON team_blabbing.id = blabbing.id
WHERE
team_id IN ($team_array) ||
mem_id='$id' ||
fromid='$logOptions_id'
ORDER BY
blab_date DESC
LIMIT 20
I know that this is messy, but i'll admit, I am no mysql veteran. I'm a beginner at best... Any suggestions?
You could put the where-clauses in subqueries:
select
*
from
(select * from ... where ...) as alias1 -- this is a subquery
left outer join
(select * from ... where ...) as alias2 -- this is also a subquery
on
....
order by
....
Note that you can't use subqueries like this in a view definition.
You could also combine the where-clauses, as in your example. Use table aliases to distinguish between columns of different tables (it's a good idea to use aliases even when you don't have to, just because it makes things easier to read). Example:
select
*
from
<table> as alias1
left outer join
<othertable> as alias2
on
....
where
alias1.id = ... and alias2.id = ... -- aliases distinguish between ids!!
order by
....
Two suggestions for you since a relative newbie in SQL. Use "aliases" for your tables to help reduce SuperLongTableNameReferencesForColumns, and always qualify the column names in a query. It can help your life go easier, and anyone AFTER you to better know which columns come from what table, especially if same column name in different tables. Prevents ambiguity in the query. Your left join, I think, from the sample, may be ambigous, but confirm the join of B.ID to TB.ID? Typically a "Team_ID" would appear once in a teams table, and each blabbing entry could have the "Team_ID" that such posting was from, in addition to its OWN "ID" for the blabbing table's unique key indicator.
SELECT
B.id,
B.mem_id,
B.the_blab,
B.blab_date,
B.blab_type,
B.device,
B.fromid,
TB.team_id
FROM
blabbing B
LEFT JOIN team_blabbing TB
ON B.ID = TB.ID
WHERE
TB.Team_ID IN ( you can't do a direct $team_array here )
OR B.mem_id = SomeParameter
OR b.FromID = AnotherParameter
ORDER BY
B.blab_date DESC
LIMIT 20
Where you were trying the $team_array, you would have to build out the full list as expected, such as
TB.Team_ID IN ( 1, 4, 18, 23, 58 )
Also, not logical "||" or, but SQL "OR"
EDIT -- per your comment
This could be done in a variety of ways, such as dynamic SQL building and executing, calling multiple times, once for each ID and merging the results, or additionally, by doing a join to yet another temp table that gets cleaned out say... daily.
If you have another table such as "TeamJoins", and it has say... 3 columns: a date, a sessionid and team_id, you could daily purge anything from a day old of queries, and/or keep clearing each time a new query by the same session ID (as it appears coming from PHP). Have two indexes, one on the date (to simplify any daily purging), and second on (sessionID, team_id) for the join.
Then, loop through to do inserts into the "TempJoins" table with the simple elements identified.
THEN, instead of a hard-coded list IN, you could change that part to
...
FROM
blabbing B
LEFT JOIN team_blabbing TB
ON B.ID = TB.ID
LEFT JOIN TeamJoins TJ
on TB.Team_ID = TJ.Team_ID
WHERE
TB.Team_ID IN NOT NULL
OR B.mem_id ... rest of query
What I ended up doing is;
I added an extra column to my blabbing table called team_id and set it to null as well as another field in my team_blabbing table called mem_id
Then I changed the insert script to also insert a value to the mem_id in team_blabbing.
After doing this I did a simple UNION ALL in the query:
SELECT
*
FROM
blabbing
WHERE
mem_id='$id' OR
fromid='$logOptions_id'
UNION ALL
SELECT
*
FROM
team_blabbing
WHERE
team_id
IN
($team_array)
ORDER BY
blab_date DESC
LIMIT 20
I am open to any thought on what I did. Try not to be too harsh though:) Thanks again for all the info.