I want to display statistics about a mysql table using this Query:
select * from t1 where product = ABC
Union
select * from t2 where product = ABC
The above query produces 2 rows with product="ABC" in t1 and 3 rows with product="ABC" in t2. The query doesn't tell me which table it came from.
How can the query be changed so I can know the source table?
You can include a unique token in each query to let you know which table the data came from like this:
select *, 't1' as tablename from t1 where product = 'ABC'
Union
select *, 't2' as tablename from t2 where product = 'ABC'
Related
I know this involves JOINS but I can't seem to find a working solution to what I'm trying to do.
I have 2 custom tables :
table1 | table2
---------------------
id id
uid uid
track_id track_id
date date
art active
info
blah
blah2
First I want to select everything WHERE uid=55 AND active=1 from table2 :
$tracks = $wpdb->get_results( "SELECT * FROM table2 WHERE uid = 55 AND active = 1");
And then match the track_id from table2 with results from table1 so I can traverse the table1 data.
I know I can do it like this :
foreach( $tracks as $track ) {
$this_track = $track->track_id;
$results = $wpdb->get_results( "SELECT * FROM table1 WHERE track_id = $this_track");
// Do stuff here
}
But this is the part where it gets tricky...
I then want to ORDER the $results from table1 by date DESC from table2
And this is where I'm lost...
Effectively I want (pseudo code) :
$results = $wpdb->get_results( "SELECT * FROM table1 WHERE track_id = $this_track" ORDER BY date DESC FROM table2);
As well as that last bit, I know I can do this entire routine with JOINS to keep this all in one query and make it way more efficient but I just don't know how.
So just to be clear, my overall routine should be like this :
Get all instances of track_id from table2 where user_id=55 and active=1, then use those results to match the track_id to every result in table1 with the same track_id and then sort the results by date back over from table2
Psuedo code, I know it contains nonsense :
$finalresults = $wpdb->get_results( "SELECT * FROM table2 where uid=55 AND active=1 THEN SELECT * FROM table1 WHERE track_id = "the track_id from the first query" THEN ORDER BY date DESC FROM table2);
Try with this query
SELECT t1.* ,t2.date AS t2date, t2.active FROM table2 AS t2 INNER JOIN table1 AS t1 ON (t1.track_id = t2.track_id) WHERE t2.uid=55 AND t2.active=1 ORDER BY t2.date DESC;
Edit: Explanation of what this query is doing. and inverted the order of the tables retrieved in the query (this don't affect the final datatset, i did this to make to follow the logic of the explanation.
1.- Begin with retrieving all rows from table2 (theres is no specific reason because i used table2 over table1, I'm only following an logical order), using the criteria that you specified iud=55 and active=1
SELECT * FROM table2 WHERE uid=55 AND active=1;
2.- but as you said you need to expand the data retrieved in table2 with some information in table1, that's exactly what it is the directive JOIN made, and we are using INNER JOIN because this type of JOIN will show rows ONLY if data for the uid=55 is present on table1, if there is NO data for the uid=55 present on both TABLES then mysql wil show empty the recordset (0 Rows selected).
in the ON(...) part I specify which criteria mysql will use to compara both tables for match in this case will compare that track_id on table2 it is the same that the specified on table1, if this codition is met then mysql considers it as a match.
anly for convenience and because i'm adding a Second table i gave an Alias to each one t1 and t2.
then the query now seems like this
SELECT * FROM table2 AS t2 INNER JOIN table1 AS t1 ON(t1.track.id = t2.track_id) WHERE t2.uid=55 AND t2.active=1;
3.- but then raise a problem, both tables has rows with the same field names, and this is something that DBMS don't like in their queries, to avoid this situation in the query i only show the fields (id, uid and track_id) from one table in this case t1 (t1.*) and only show the fields that doesn't have this problem from t2 (t2.date AS t2date, t2.active). in this way mysql won't throw any error.
SELECT t1.* ,t2.date AS t2date, t2.active FROM table2 AS t2 INNER JOIN table1 AS t1 ON (t1.track_id = t2.track_id) WHERE t2.uid=55 AND t2.active=1;
4.- for the final step i specify to mysql that i want all found rows ordered descent by a field in the table2;
ORDER BY t2.date DESC;
then this criteria will be applied to the whole selected rows. and the final query has this form.
SELECT t1.* ,t2.date AS t2date, t2.active FROM table2 AS t2 INNER JOIN table1 AS t1 ON (t1.track_id = t2.track_id) WHERE t2.uid=55 AND t2.active=1 ORDER BY t2.date DESC;
if is not completely clear you can ask ...
I have two tables I want to display datas which are not in table 2 but exist in table 1 and after listing the datas.I want to add those datas in table 2.
which join shall i use?please help me with the code
You need no join at all. You want data from table1 where no entry exists in table2. So use the EXISTS clause.
select something
from table1
where not exists
(
select *
from table2
where table2.somekey = table1.somekey
);
As to the insert:
insert into table2 (column names)
select something
from table1
where not exists
(
select *
from table2
where table2.somekey = table1.somekey
);
I am having a problem with not been able to display all records from table1.
I have 2 tables.
Table 1 and 2 and I want to display all the records from table 1 (Even if some records donly exists on table1 and no reference in table2)
This is what I am trying and I have 2 recording in Table1 but it's only displaying 1.
1 record is joined by the name_id on table1 and table2 and the other record only exists on table1 BUT I need to display both.
Here is the query:
$query = mysql_query("SELECT
table1.name_id,
table2.name_id,
FROM `table1`
LEFT JOIN `table2` ON table1.name_id=table2.name_id
");
How can I get it so it will display all the records from table1 (The one's that are join and the ones that are not too) ?
you can use "JOIN" to fetch data from both table as
$query = mysql_query("SELECT table1.name_id, table2.name_id FROM `table1` JOIN `table2` ON `table1`.`name_id`=`table2`.`name_id` ");
I need to query the database to pull all cars that a particular user likes.
I know that user_id is 1
Then I have 2 tables. 1 contains all the cars ... id and description and table 2 contains the likes.
Table 1 has a list if cars and these fields:
car_id
car_name,
car_description
Table 2 has what cars I like and these fields:
user_id
car_id
likes (1 or 0)
So I need to pull out only the records that user 1 likes from Table 2 but only the ones he likes
What SQL query would I need to do for that?
SELECT * FROM table1 as t0
LEFT JOIN table2 as t1 on t0.car_id = t1.car_id
WHERE t1.likes = 1
Try this
SELECT * FROM table1 as t1 LEFT JOIN table2 as t2 on t1.car_id = t2.car_id WHERE t2.user_id = $user_id
Try this query
SELECT t1.*,t2.*
FROM tbl1 t1,tbl2 t2
WHERE likes = 1 AND user_id = 1 AND t1.car_id = t2.car_id
If I have a list of ID's that I have selected from a statement
SELECT id FROM myTable WHERE name = 'TEST'
This would return just the ids (1001, 1002, 1003, etc...) Then I want to perform another SELECT statement to retrieve all the titles for all those ids.
SELECT title FROM myTable2 WHERE id = XXXX
the id in table2 is the foreign key of table2. id in myTable is the Primary Key. How can I go about retrieving all the titles from those ids. I was thinking about storing all the results of the first select statement in an array, and then using a while loop to iterate through the list and return each result into another array, but my fear is that when the database gets big if it has to return 1000 rows that could be some bad overhead. So in PHP or SQL what is the best way to perform this?
You can use a subquery:
SELECT title
FROM myTable2
WHERE id IN (
SELECT id
FROM myTable
WHERE name = 'TEST'
)
Another way to do it would to be use a JOIN, to avoid the sub-query:
SELECT title
FROM myTable2
LEFT JOIN myTable
ON myTable.id = myTable2.id
WHERE myTable.name = 'TEST'
You should just be able to select them at the same time.
SELECT a.id, b.title
FROM myTable a, myTable2 b
WHERE a.name = 'TEST' AND b.id = a.id;
to select both:
SELECT id, title FROM mytable WHERE name="TEST"
or to select the whole row
SELECT * FROM mytable WHERE name="TEST"
if its two tables you are selecting from:
SELECT id, title FROM mytable A JOIN mytable2 B USING (id)