I have two tables: projects and user_licenses.
I'd like to grab the entire list of projects from the database, as well as the user's current license state. The licenses table has a user ID field which I check against a $_SESSION variable for the value. The thing is, they might not have a license, or a non-logged in visitor may want to see the projects list. My question is this: How can I get the data from the left table always display, but only grab data for that row from the right table when certain conditions are met?
The query I have at the moment is this:
SELECT Projects.*,
UserLicenses.*
FROM Projects
LEFT JOIN UserLicenses ON Projects.id = UserLicenses.project_id
WHERE UserLicenses.user_id = 12
ORDER BY name ASC
Add any extra conditions to the on clause of the left join. They will only affect the joined table.
SELECT Projects.*,
UserLicenses.*
FROM Projects
LEFT JOIN UserLicenses
ON Projects.id = UserLicenses.project_id
and UserLicenses.user_id = 12
and UserLicences.Question = '6*7'
and UserLicences.Answer = 42
ORDER BY name ASC
This will return projects without matching licenses.
Move the UserLicenses condition away from WHERE, and up to the JOIN condition. By having it in the WHERE part, you will never see those "left" rows because they are filtered away.
You can also probably use WHERE (UserLicenses.user_id = 12 OR UserLicenses.user_id IS NULL)
Don't do that. Just move it to the join condition like this:
LEFT JOIN UserLicenses ON
(Projects.id = UserLicenses.project_id AND UserLicenses.user_id = 12)
You can use LEFT JOIN
If its conditions match then values show otherwise null value shows.
Related
I'm joining two tables together, a "Photos" table and "Locations" table. Each location may or may not have a default picture associated with it, and if it does I want to return that photo name. If it doesn't then return null. The default image for each location (if it exists) is always the image that has the "PictureSort" value of 1.
From my first SQL attempt below, if I use a WHERE statement, then I don't receive the null locations (where photos don't exist for that location).
SELECT a.LocationID, a.LocationName, b.PictureSort, b.PictureName
FROM Locations AS a
LEFT JOIN Photos AS b ON a.LocationID = b.LocationID
WHERE b.PictureSort = '1'
GROUP BY a.LocationID
I also tried using the MIN() function in mySQL to say show me the lowest value in the PictureSort column, and while that works for that column, the column right next to it PictureName doesn't follow suit and return the associated value to the PictureSort column.
SELECT a.LocationID, a.LocationName, MIN(b.PictureSort) AS PictureSort, b.PictureName
FROM Locations AS a
LEFT JOIN Photos AS b ON a.LocationID = b.LocationID
GROUP BY a.LocationID
Any help is greatly appreciated. I want this to work, but I'm also looking for the least expensive query possible to get this done.
Thanks!
Conditions on the second table should be in the on clause for a left join.
Also, your table aliases should be related to the names of the table. And the GROUP BY should not be needed. So try this:
SELECT l.LocationID, l.LocationName, p.PictureSort, p.PictureName
FROM Locations l LEFT JOIN
Photos p
ON p.LocationID = l.LocationID AND b.PictureSort = '1';
If PictureSort is stored as a number, then drop the single quotes. Don't mix data types.
I have two tables usersin and usersout(I can not change schema, a lot of system changes must be done in php otherwise). I should get all user records in a query but I should mark them if they are in or out also a user may have an in record and out record I shouldn't show in record if has an out record.
I have created tables with sample data in SQL Fiddle: http://www.sqlfiddle.com/#!9/ac99a/1/0
Can u help me how can I remove duplicates of user records in this union query?
If you want to have all entries with an entry in either the in or out table, but not in both of them, then a full outer join would be your friend.
Since MySQL does not know that kind of join, you can emulate it with a left outer join and a right outer join combined like so:
SELECT
ui.id, ui.user, 'i'
FROM
usersIN ui
LEFT OUTER JOIN
usersOUT uo ON ui.user = uo.user
WHERE uo.id IS NULL
UNION
SELECT
uo.id, uo.user, 'o'
FROM
usersIN ui
RIGHT OUTER JOIN
usersOUT uo ON ui.user = uo.user
WHERE ui.id IS NULL;
This should give you the right output.
A good visual explanation of joins can be found here
I'm not sure if this is possible exactly as stated in the title, but what I'm trying to accomplish, however possible, is what would amount to left joining two columns from one table, each on a separate table.
Here's the statement I'm working with. Unfortunately, MySQL doesn't allow me to actually do this and gives me an error message. Is there another way to accomplish what I want? Is my syntax perhaps just off?
select h.HITTER_ID, u.UMPIRE_ID, u.HAND_B
from
hitters h,
schedules sched
LEFT JOIN
umpires u
ON sched.home_base_umpire_id = u.UMPIRE_ID and h.HAND_B = u.HAND_B
In the umpires table, each UMPIRE_ID appears twice, once with HAND_B = "R" and once with HAND_B = "L"
Essentially, I want to:
1) Pull the UMPIRE_ID from umpires when that UMPIRE_ID appears in schedules
2) Of the two UMPIRE_ID records, select the one with the HAND_B field that corresponds to the HAND_B field in hitters
I could put the "h.HAND_B = u.HAND_B" in the where clause, but that would require that the UMPIRE_ID not be NULL, and I need to leave open the possibility that it is NULL.
How can I accomplish this?
You need to modify your query to be like below
select h.HITTER_ID,
u.UMPIRE_ID,
u.HAND_B
from hitters h
left join umpires u on h.HAND_B = u.HAND_B
left join schedules sched ON sched.home_base_umpire_id = u.UMPIRE_ID;
I'm using 3 tables to collect data from. The proces looks like:
User write VIN to form
Script search in table 1 for case_id and country base on that vin
number
After that he use case_id and country for search in table number 2
and get calculation id from there
Base on that calculation id and case id it search in 3th table
.
My script looks like this:
SELECT
cases.case_id,
cases.lastcalc_model_options,
cases.country,
calculations.calculation_id,
calculations.license,
positions.text
FROM cases
INNER JOIN calculations ON(cases.case_id =calculations.case_id
AND cases.country = calculations.country)
INNER JOIN positions ON(calculations.case_id = positions.case_id
AND calculations.calculation_id = positions.calculation_id)
WHERE vin ='ABCDEFGH'
This select work correctly, problem start when for example there is for example no result in table positions with that case_id and calculation_id. Instead of give back atleast everything it found in other tables it return NOTHING.
Is there a way to change this kind of komplex SELECT to return everything it found not return something only when every condition is TRUE?
Your problem is the INNER JOIN. Using INNER JOIN your result only contains entries present in all tables. Try using LEFT JOIN instead.
SELECT
cases.case_id,
cases.lastcalc_model_options,
cases.country,
calculations.calculation_id,
calculations.license,
positions.text
FROM cases
LEFT JOIN calculations ON(cases.case_id =calculations.case_id
AND cases.country = calculations.country)
LEFT JOIN positions ON(calculations.case_id = positions.case_id
AND calculations.calculation_id = positions.calculation_id)
WHERE vin ='ABCDEFGH'
See this stackoverlow answer for some more indepth information.
INNER JOIN returns rows from both tables only if there is a match between the columns in both tables.
You may try LEFT JOIN or FULL OUTER JOIN instead.
SELECT submissions.created_at, guests.accepted
FROM submission
INNER JOIN guests
ON guests.event_id = 1
ORDER BY submissions.created_at ASC;
Currently this query is taking a long time to run (may not even return everything).
What I am trying to accomplish:
Grab the field submissions.created at and guests.accepted (the two are linked by a submission_id)
given a certain event_id (event 1 for example).
What is wrong with my query?
You forgot to give the JOIN condition in your query. Try this:
SELECT submissions.created_at, guests.accepted
FROM submission s
INNER JOIN guests g on g.event_id = s.submissions_id
where guests.event_id = 1
ORDER BY submissions.created_at ASC;
SELECT submissions.created_at, guests.accepted
FROM submission
INNER JOIN guests
ON guests.(column to match against) = submissions.(column to match on)
where guests.event_id=1
ORDER BY submissions.created_at ASC;
As many others here have already said, your join is a little goofed. It's attempting to join the one row that matches in the guests table against every single row in the submission column.
You would need to do your join like this :
Inner join guest on guest.event_id = submissions_id
where guest.event_id = 1
When you join you need to join on two columns from different table (most of the time id columns)
You can read the MySQL example for more explanation. And here is the link to the MySQL reference manual