so I'm having trouble selecting a field only if another fields value is not equal to 0.
So, here's what's going on.
I have 3 tables, they are - users, schools, campuses
And basically, I need to select a single users data from these 3 tables. I'd like to only select the campus_name field from campuses if the users.campus_id field is not 0.
So, something pseudo coded like this might give you a better idea..
The query is being passed in a $id variable, that has some user's id.
SELECT users.*, schools.*, (if(users.campus_id != 0) then campuses.campus_name)
FROM users, schools, campuses
WHERE users.id = '$id' (if(users.campus_id != 0) then AND campuses.id = users.campus_id)
SELECT *
FROM schools,
users LEFT OUTER JOIN campuses
ON users.campus_id != 0
AND users.campus_id = campuses.id
WHERE users.school_id = schools.id
So you are joining three tables together, you always expect a user to have a school, but they may not have a campus, and if this is the case, obviously nothing should be displayed.
The best you can do is acheive this with a LEFT JOIN on campuses.
An example based on your pseudo code below:
SELECT u.*, s.*, c.campus_name
FROM users u
INNER JOIN schools s ON u.school_id = s.school_id
LEFT JOIN campuses c ON u.campus_id = c.campus_id
WHERE u.user_id = $userId
If I understood you correctly, you want ALL the information displayed, but to display campus name ONLY if it exists? If so, I believe the following statement should do the trick:
SELECT `u`.* `s`.* if(`c`.`campus_name` != 0, `c`.`campus_name`, "") as `campus`
FROM `users` as `u`
INNER JOIN `schools` as `s` ON `u`.`school_id` = `s`.`school_id`
LEFT JOIN `campuses` as `c` ON `u`.`campus_id` = `c`.`campus_id`
WHERE `u`.`user_id` = $user_id;
Untested, written from the top of my head, could be errors in there
Related
I've tried to get data from from one table if id of 2 tables equals to each other. Here is the code which I used:
SELECT id_to
, email_to
, name_to
, status_to
FROM users
LEFT
JOIN friends
ON users.id = friends.id_from
WHERE id_from = ?
I used LEFT JOIN to join two tables but it gets the values from the friends(table) instead of users(table).
I think I've explained my problem clearly.
I guess you must specify it on your query, like this:
SELECT users.id_to, users.email_to, users.name_to, user.status_to FROM users LEFT JOIN friends ON users.id = friends.id_from WHERE id_from = ?
You can do the same if you need to retrieve values from 'friends' table.
If both tables have the same column, then you can specify the table name while selecting columns. so your code will look like:
SELECT users.id_to, users.email_to, users.name_to, user.status_to FROM users LEFT JOIN friends ON users.id = friends.id_from WHERE friends.id_from = ?
I have a query that looks up people's full names based on their record ID's in a table called users. The full names are tied to their roles in another table (table1). This requires multiple joins to the users table:
SELECT table1.id, users.full_name AS "Requester",
users.full_name AS "Approver,"
users.full_name AS "Ordered By",
users.full_name AS "Received By"
FROM table1
JOIN users AS users
ON table1.requester_id = users.id
JOIN users AS users2
ON table1.approver_id = users2.id
JOIN users AS users3
ON table1.ordered_by = users3.id
JOIN users AS users4
ON table1.received_by = users4.id
WHERE table1.deleted_record !=1;
The problem I'm having is with ordered_by and received_by. Often, they don't yet exist, because the order has neither been ordered nor received, so the ID for each can be 0, which has no corresponding value in the userstable. When I run this query, I should get back all 475 records that exist, but I only get back 365, because of those 0 values. How can I modify this query to make sure all rows are returned, even if ordered_by and/or received_by = 0?
First, your primary table driving the query should be table1. Then, you are using JOIN instead of LEFT JOIN. LEFT JOIN will give you a null result if no link, but not fail. In which case, you might have to use an IF for your fields value
SELECT table1.id, req.full_name AS "Requester",
app.full_name AS "Approver",
ordr.full_name AS "Ordered By",
rec.full_name AS "Received By"
FROM table1
LEFT JOIN users AS req
ON table1.requester_id = req.id
LEFT JOIN users AS app
ON table1.approver_id = app.id
LEFT JOIN users AS ordr
ON table1.ordered_by = ordr.id
LEFT JOIN users AS rec
ON table1.received_by = rec.id
WHERE table1.deleted_record !=1;
This should do it
You are looking for left join:
SELECT t1.id, ur.full_name AS "Requester",
ua.full_name AS "Approver,"
uo.full_name AS "Ordered By",
urv.uo AS "Received By"
FROM table1 t1 LEFT JOIN
users ur
ON t1.requester_id = ur.id LEFT JOIN
users ua
ON t1.approver_id = ua.id LEFT JOIN
users uo
ON t1.ordered_by = uo.id LEFT JOIN
users urv
ON t1.received_by = urv.id
WHERE t1.deleted_record <> 1;
Note that I changed the aliases on the users references from fairly meaningless u1, u2, etc. to ua, uo, and so on. Also, these need to be used in the SELECT to get the right full name.
I have two tables: publick_feed and users
I want to SELECT all from public_feed and also SELECT a three columns from users whose id is the same of user_id in public_feed
and assign the rows returned from public_feed to the column in users table ( correspondent)
I try this:
<?php
$sql = "
SELECT * FROM public_feed
WHERE user_id IN
(SELECT id FROM users) AND
(SELECT Firstname,Lastname,Avatar FROM users WHERE id IN(SELECT user_id FROM public_feed))
";
$query = mysqli_query($dbc_conn,$sql);
if(mysqli_num_rows($query) > 0){
while($row = mysqli_fetch_assoc($query)){
//echo rows with correspondent details from the users table
echo $row['user_id'];
}
}
<?
Please any help will be much appreciated.
Thank you.
Or version with left join in case if there is no user in public_feed, and you still want to fetch user data
SELECT
u.*, f.*
FROM
public_feed f LEFT JOIN
users u ON f.user_id = u.id;
Because author asked for explanation, here it is:
First we are going to use table name alias to make query shorter
public_feed f
and
users u
we are saying that want to refer to tables with an alias. Of course * means that we want to select all columns
SELECT users.*, public_feed.*
is equal to
SELECT u.*, f.*
Of course you can use any other letters as an alias
Next we are saying that public_feed.user_id must be equal to users.id. But when public feed entry does not exists just display columns with null values. This is why we are using LEFT JOIN instead of INNER JOIN. In general JOINS are used to fetch related data from more than one related tables.
ON keyword is saying values from which columns in the tables must be equal to satisfy the request
I think doing a join would be cleaner than using a complicated subquery:
SELECT u.Firstname,
u.Lastname,
u.Avatar,
COALESCE(pf.User_id, 'NA'),
COALESCE(pf.Post, 'NA'),
COALESCE(pf.Date, 'NA')
FROM users u
LEFT JOIN public_feed pf
ON u.Id = pf.User_id
I chose a LEFT JOIN of users against public_feed on the assumption that every feed will have an entry in the users table, but not necessarily vice-versa. For those users who have no feed entries, NA would appear in those columns and that user would appear in only a single record.
I have fetched the data from two different tables is this.
But now, I want the following result with their original names and not the numbers like status 1 is for Good, and user_id=1 means "Mike".
To select usernames using userID try using an inner join
And/or you can say 1 = good like so:
if($status == 1)
{
echo "Good";
}
(though this can also be done with the inner join, if you have the values in another table ofcourse)
Just JOIN your tables, something like:
SELECT f.FollowDate, s.StatusName, u.UserName
FROM Folowers f
INNER JOIN Users u ON f.UserId = u.ID
INNER JOIN Statuses s ON f.StatusID = s.ID
Im trying to construct a query that goes over 3 tables and im COMPLETELY stumped ... my knowledge limit is basic 1 table query and i need some help before i stick my head in a blender.
I have the following query
SELECT * FROM internalrole WHERE introle = $imarole
Im fine with that part .. its the next thats getting me all stressed.
That query returns the following columns ( id, user_id, introle, proven, used )
What i then need to do is take the user_id from the results returned and use it to get the following
SELECT * FROM users WHERE id = user_id(from previous query) AND archive = 0 and status = 8
I need to put that into 1 query, but wait, theres more .... from the results there, i need to check if that user's 'id' is in the availability table, if it is, check the date ( column name is date ) and if it matches todays date, dont return that one user.
I need to put all that in one query :S ... i have NO IDEA how to do it, thinking about it makes my head shake ... If someone could help me out, i would be eternaly grateful.
Cheers,
Use INNER JOIN, which links tables to each other based on a common attribute (typically a primary - foreign key relationship)
say an attribute, 'id', links table1 and table2
SELECT t1.att1, t2.att2
FROM table1 t1
INNER JOIN table2 t2
ON t1.id = t2.id --essentially, this links ids that are equal with each other together to make one large table row
To add more tables, just add more join clauses.
SELECT u.*
FROM internalrole ir
INNER JOIN users u
ON ir.user_id = u.id
AND u.archive = 0
AND u.status = 8
LEFT JOIN availability a
ON ir.user_id = a.user_id
AND a.date = CURDATE()
WHERE ir.introle = $imarole
AND a.user_id IS NULL /* User does NOT exist in availability table w/ today's date */
EDIT: This second query is based on the comments below, asking to show only users who do exist in the availability table.
SELECT u.*
FROM internalrole ir
INNER JOIN users u
ON ir.user_id = u.id
AND u.archive = 0
AND u.status = 8
INNER JOIN availability a
ON ir.user_id = a.user_id
WHERE ir.introle = $imarole
Hmm, maybe something like this
SELECT * FROM users WHERE id IN (SELECT user_id FROM internalrole WHERE introle = $imarole) AND archive = 0 and status = 8;
A handy thing for me to remember is that tables are essentially arrays in SQL.
HTH!
Nested queries are your friend.
SELECT * FROM users WHERE id in (SELECT user_id FROM internalrole WHERE introle = $imarole) AND archive = 0 and status = 8
Alternatively joins:
SELECT * FROM users INNER JOIN internalrole ON users.id = internalrole.user_id WHERE internalrole.user_id = $imarole AND users.archive = 0 and users.status = 8