Table: team
id | name
---------
1 | team a
2 | team b
3 | team c
Table: event
home & away are foreign key of team
id | home | away
----------------
1 | 2 | 3
2 | 1 | 2
3 | 3 | 1
What I want to get:
id | home | away
------------------
1 | team b | team c
2 | team a | team b
3 | team c | team a
Can anyone please teach me how to write the query to get the latest table based on the structure of this 2 tables. Thanks.
You need to join twice:
select e.id, th.name as home, ta.name as away
from event e join
team th
on e.home = th.id join
team ta
on e.away = ta.id;
Note that the two instances of team in the from clause have different table aliases. That makes it possible to distinguish between those references when referencing columns.
Related
My question is: Can I do this?
I try many things, some of them are:
Search 1
Search 2
Search 3
Search 4
I need all the info form Table A, and sometimes I need to join this table with Table B. My problem is that when I join both tables, if an specific parameter in Table A is not in Table B just give me the records when the specific parameter are, but I want all the records.
Table A
|--------------------------------|
| Table A |
|-------------------|------------|
| id_table_A | name | id_table_B |
|------------|------|------------|
| 1 | Joe | 1 |
|------------|------|------------|
| 2 | Ben | |
|------------|------|------------|
| 3 | Lya | |
|------------|------|------------|
| 4 | luis | 2 |
|------------|------|------------|
Table B
|----------------------|
| Table B |
|----------------------|
| id_table_B | Elements|
|------------|---------|
| 1 | Car |
|------------|---------|
| 2 | Byke |
|------------|---------|
| 3 | Moto |
|------------|---------|
What I want to show in my View is this:
|------------|------|------------|
| id_table_A | name | Elements |
|------------|------|------------|
| 1 | Joe | Car |
|------------|------|------------|
| 2 | Ben | |
|------------|------|------------|
| 3 | Lya | |
|------------|------|------------|
| 4 | luis | Byke |
|------------|------|------------|
My model
In my model this is what I tried:
"SELECT * FROM table_A, table_B where table_A.id_table_B = table_B.id_table_B"
But this query only show me data 1 and 4.
This can be done or not?
Thanks in advance.
You can use left join
SELECT *
FROM table_A
left join table_B on table_A.id_table_B = table_B.id_table_B
Left join is used when the keys between tables may not always match. In this case, the left join retrieves the correct match where it's possible and the values become NULL when not possible.
SQL LEFT JOIN Documentation
You need an explicit LEFT JOIN as opposed to the implicit INNER JOIN that is used when you simply list the tables like that. https://www.w3schools.com/sql/sql_join_left.asp
I have issue getting results from two database table. here is what i have:
table A: 'courses'
math | history | geography | computer
1 | 2 | 3 | 4
and Table B
user_id | classroom_id | course
1 | 5 | 3
1 | 5 | 4
1 | 6 | 2
I returned the table A on a for each loop but I would like to check what courses the user 1 has to return true or false on any Table a columns.
Any help appreciated.
I need help not negative votes :(
You have your database set up wrong I believe. What you want is something like
Table_A:
PKEY | Course
1 | Math
2 | History
3 | Geography
4 | Computer
Table_B:
user_id | classroom_id | course
1 | 5 | 3
1 | 5 | 4
1 | 6 | 2
Then you could do something like
SELECT
TableA.PKEY,
TableA.Course,
TableB.user_id,
TableB.classroom_id,
TableB.course,
FROM TableA
LEFT JOIN TableB
ON TableA.PKEY = TableB.course
^^This will return the data from BOTH tables.
you see this line
ON TableA.PKEY = TableB.course
^^This is called the foreign key.
BIG GOTCHA: Make SURE that the columns for both of those ^^^ are set up EXACTLY the same. For instance, IF TableA.PKEY is an UNSIGNED INT(10), then TableB.course MUST also be UNSIGNED INT(10). They have to be identical for the join to work correctly.
Hi I have 2 table Offense table and User_jobs table
offense table:
crime_id |crime_type |casenumber|
---------+-----------+----------+
1 | 3 |1 |
2 | 3 |1 |
1 | 3 |2 |
12 | AA |2 |
user_jobs table:
casenumber |disposal_status |
-----------+----------------+
1 | yes |
1 | yes |
2 | no |
2 | no |
what i want is to count the number of rows with the same combination say crime_id=1 and crime_type= 3 but these must have a disposal status of yes in the user_jobs table.
i want to do this in mysql. pliz help
sorry but i am new to mysql. i now want to display the real names of those id not the id themselves.
the tables with these IDs are crime_category and Crime_type Crime_catgory
table:
category |crime_id |
-----------+----------------+
theft | 1 |
murder | 2 |
rape | 3 | 2 |
no |
Crime_type table:
Crime_type |id |
---------------+----------------+
administrative | yes |
criminal | yes |
You can do this with a simple inner join and an aggregate function:
select
o.crime_id,
o.crime_type,
count(*)
from
offence o
join user_jobs uj
on o.casenumber=uj.casenumber
where
uj.disposal_status='Yes'
group by
o.crime_id,
o.crime_type
This will pick up distinct combinations of the first two columns joined as they should tot he jobs table and only where the disposal_status is equal to 'Yes'
Edit: You would probably do really well to have a read of this Q&A that I put together for exactly this sort of situation - where I give you the code for it, but would like to explain this is a lot more detail. The Q&A explains why this type of thing (and many many others) work and how they do so:
How can an SQL query return data from multiple tables
Edit 2:
select
o.crime_id,
o.crime_type,
ct.category,
count(*)
from
offence o
join user_jobs uj
on o.casenumber=uj.casenumber
join crime_type ct
on o.crime_type=ct.crime_id
where
uj.disposal_status='Yes'
group by
o.crime_id,
o.crime_type,
ct.category,
This is an example MYSQL result
+----+---+
| A | B |
+----+---+
| 1 | 1 |
| 1 | 2 |
| 2 | 3 |
| 2 | 4 |
| 3 | 5 |
+----+---+
I would like to run through every distinct in Column A and do something utilizing the values in Column B.
Let's say A has userids and B has foods. I would like to grab all the foods that user 1 likes and then shoot an email to 1, then grab all the foods that user 2 likes and email to her, and so forth. Would appreciate any suggestions.
If you want comma separated values, you can use GROUP_CONCAT
SELECT A, GROUP_CONCAT(DISTINCT B) foodList
FROM tableName
GROUP BY A
SQLFiddle Demo
Other Link
GROUP BY clause
I have the two following tables
table A
| id | name |
| 1 | bob |
| 2 | jill |
| 3 | jojo |
Table A is displayed by using checkboxes.
On the first go, the user checks all three checkboxes so you get the result in table B.
table B
| table_a_id | table_c_id |
| 1 | 2 |
| 2 | 2 |
| 3 | 2 |
But the next time the user goes to edit, they UNCHECK '2' so that it's only:
1
3
How do I write my query (using either mySQL or php) so that TABLE B is updated to:
| table_a_id | table_c_id |
| 1 | 2 |
| 3 | 2 |
DELETE A,B
FROM A
LEFT JOIN B
ON B.table_a_id = A.id
WHERE A.id NOT IN (1,3)
Or use InnoDB with a Foreign key ON DELETE CASCADE, much simpler :)
DELETE
FROM TableB
WHERE (NOT table_a_id IN (1, 3))
AND (table_c_id = 2)