I have a mysql table that looks something like this:
id | name
---+-------
1 | cola
2 | pepsi
3 | sprite
and another table:
customer | buy1 | buy2
---------+------+-----
Jhon | 2 | 3
Alice | 1 | 3
Tony | 3 | 2
I want to join the two tables and generate
customer | buy1 | buy2
---------+-------+--------
Jhon | Pepsi | Sprite
Alice | Cola | Sprite
Tony | Sprite| Pepsi
SELECT C.customer, REF.NAME, REF2.NAME
FROM OTHER_TABLE AS C
JOIN TABLE_SOMETHING_LIKE_THIS AS REF ON C.BUY1 = REF.ID
JOIN TABLE_SOMETHING_LIKE_THIS AS REF2 ON C.BUY2 = REF2.ID
You can write subqueries in a select list like this:
select
customer,
(select name from tbl1 where id = buy1) buy1,
(select name from tbl1 where id = buy2) buy2
from
tbl2;
Related
I'm in front of a "minor" problem taht looks easy but I didn't suceed to resolve it.
I have three tables in my Database :
Table gp
____________
id | name |
____________
1 | Le Mans|
2 | Toulon |
3 | Rennes |
Table player
____________
id | name |
____________
1 | Thibaut|
2 | Fred |
3 | Samir |
Table Records
_____________________________
id | gp_id | player_id | time
_____________________________
1 | 1 | 1 | 17860
2 | 2 | 1 | 11311
3 | 3 | 1 | 33133
4 | 3 | 2 | 11113
5 | 2 | 2 | 44444
6 | 1 | 2 | 13131
7 | 1 | 3 | 11111
8 | 3 | 3 | 21112
I want to get a sum of time for players that have a record on every gp ( so in my case, just players Thibaut and Fred have a record on the 3 gp ( Samir has just a record on two gp ) ).
I have no idea how I can get that, of course this SQL query is retrieving a sum but from this query I want to escape the guys that don't have a record on every GPs, but I'm blocked at that point ...
SELECT p.name, sum(time)
from records r
join gp g on r.gp_id = g.id
join player p on r.player_id = p.id
group by r.player_id
Thanks in advance guys !
You could use having count to exclude the records that don't have a record on every GPs.
Try:
select p.name,
sum(`time`) as tot_sum
from records r
inner join player p on r.player_id=p.id
inner join gp g on g.id=r.gp_id
group by p.name
having count(distinct gp_id) = (select count(distinct id) from gp)
https://dbfiddle.uk/t8QwSFDY
having count(distinct gp_id) = (select count(distinct id) from gp) will match only the records in the record table that have a record on every gp.
Let suppose
'Mary is a teacher in a middle school and she has a table seat storing students' names and their corresponding seat ids. The column id is a continuous increment. Mary wants to change seats for the adjacent students.'
The sample table looks like this:
+---------+---------+
| id | student |
+---------+---------+
| 1 | Doris |
| 2 | Abbot |
| 3 | Green |
| 4 | Emerson |
| 5 | Jeames |
+---------+---------+
Mary wants to switch Adjacent Student, the output looks like this:
+---------+---------+
| id | student |
+---------+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+---------+---------+
I have come up with the solution using Case When and Then statement.
Solution :
SELECT
CASE
WHEN((SELECT MAX(id) FROM seat)%2 = 1) AND id = (SELECT MAX(id) FROM seat) THEN id
WHEN id%2 = 1 THEN id + 1
ELSE id - 1
END AS id, student
FROM seat
ORDER BY id
Is there any other easy way using case statement or any other approach through which we can solve this problem.
Thanks
You can use a combination of self join using LEFT JOIN, CASE WHEN and COALESCE as alternative.
select s1.id, coalesce(s2.student,s1.student)
from sample s1
left join sample s2
on s1.id + case when s1.id%2=1 then 1 else -1 end = s2.id
COALESCE and LEFT JOIN are just needed to keep the record for Jeames, which not join with s2
You can test on this db<>fiddle.
You can use lead() and first_value():
select id,
coalesce(lead(student) over (order by id),
first_value(student) over (order by id)
) as student
from t;
I have a table A that contains tree columns, id, users ids and vehicle id. And a table B that contains vehicleid, and vehicle name.
Table A
---------------------------
| Id | User_id |Vehicle_id|
---------------------------
| 1 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 4 |
| 4 | 2 | 2 |
| 5 | 2 | 3 |
| 6 | 4 | 5 |
---------------------------
Table B
-------------------
| Id |Vehicle_name|
-------------------
| 1 | Car |
| 2 | Bike |
| 3 | Plane |
| 4 | Boat |
| 5 | Rocket |
-------------------
Given a user id, I need to get all vehicle names, that doesn't match with table A. I've tried Outer joins, but I can't manage to do get the info that i need.
For example: Given user id 1, the query should return Car and Rocket.
thanks in advance
This is simple enough using not in or not exists:
select b.*
from b
where not exists (select 1
from a
where a.vehicle_id = b.id and a.user_id = #a_user_id
);
I also thought of using a cross join and was able to get the output in case you are more comfortable with join logic.
SELECT CJOIN.USER_ID, CJOIN.VEHICLE_ID, CJOIN.VEHICLE_NAME
FROM
(SELECT DISTINCT A.USER_ID, B.ID AS VEHICLE_ID, B.VEHICLE_NAME FROM TABLE_A A CROSS JOIN TABLE_B B) CJOIN
LEFT JOIN
TABLE_A D
ON CJOIN.USER_ID = D.USER_ID AND CJOIN.VEHICLE_ID = D.VEHICLE_ID
WHERE D.USER_ID IS NULL AND D.VEHICLE_ID IS NULL;
First, I got all possible combinations of USER_ID x VEHICLE_ID by a cross join and used this table in a left join to pull records for which there is no match.
Say I have two tables --people and pets-- where each person may have more than one pet:
people:
+-----------+-------+
| person_id | name |
+-----------+-------+
| 1 | Bob |
| 2 | John |
| 3 | Pete |
| 4 | Waldo |
+-----------+-------+
pets:
+--------+-----------+--------+
| pet_id | person_id | animal |
+--------+-----------+--------+
| 1 | 1 | dog |
| 2 | 1 | dog |
| 3 | 1 | cat |
| 4 | 2 | cat |
| 5 | 3 | dog |
| 6 | 3 | tiger |
| 7 | 3 | tiger |
| 8 | 4 | tiger |
| 9 | 4 | tiger |
| 10 | 4 | tiger |
+--------+-----------+--------+
I'm trying to select the people who ONLY have tigers as pets. Obviously the only one that fits this criteria is Waldo, since Pete has a dog as well... but I'm having some trouble writing the query for this.
The most obvious case is select people.person_id, people.name from people join pets on people.person_id = pets.person_id where pets.animal = "tiger", but this returns Pete and Waldo.
It would be helpful if there was a clause like pets.animal ONLY = "tiger", but as far as I know this doesn't exist.
How could the query be written?
select people.person_id, people.name
from people
join pets on people.person_id = pets.person_id
where pets.animal = "tiger"
AND people.person_id NOT IN (select person_id from pets where animal != 'tiger');
Use group by and having:
select p.person_id
from pets p
group by p.person_id
having max(animal) = 'tiger' and min(animal) = 'tiger';
select distinct person_id
from pets
where animal = "tiger"
intersect
select distinct person_id
from pets
where animal = "tiger"
and person_id not in
(select person_id from pets where animal <> "tiger")
You can use intersect to select a person who only has tiger as his pet.
SELECT *
FROM people pp
WHERE EXISTS (SELECT * FROM pets pt
WHERE pt.person_id = pp.person_id
AND pt.animal = 'tiger'
)
AND NOT EXISTS (SELECT * FROM pets pt
WHERE pt.person_id = pp.person_id
AND pt.animal <> 'tiger'
);
If every person was guaranteed to have at least one pet, then the query could be as simple as:
select name
from people
where not exists (select 1
from pets
where pets.person_id = people.id and
pets.animal != 'tiger')
Or: return the people for whom there is no record that is not a tiger.
NOT EXISTS is executed as a very efficient anti-join, in which each row from people would be rejected as soon as a single non-tiger pet was found.
Say I have a database that has people, grocery stores, and items you can buy in the store, like so:
Stores People Foods
----------------- ------------------ ------------------
| id | name | | id | name | | id | name |
----------------- ------------------ ------------------
| 1 | Giant | | 1 | Jon Skeet | | 1 | Tomatoes |
| 2 | Vons | | 2 | KLee1 | | 2 | Apples |
| 3 | Safeway | ------------------ | 3 | Potatoes |
----------------- ------------------
I have an additional table which keep track of which stores sell what:
Inventory
--------------------
| store_id| food_id|
--------------------
| 1 | 1 |
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
| 3 | 2 |
| 3 | 3 |
--------------------
And I have another table that has shopping lists on it
Lists
---------------------
| person_id| food_id|
---------------------
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 3 |
---------------------
My question is, given a person, or their id, what is the best way to figure out what stores they can go to so they will get everything on their list. Is there a pattern for these types of computations in MySQL?
My attempt (very ugly and messy) is something like:
-- Given that _pid is the person_id we want to get the list of stores for.
SELECT stores.name, store_id, num, COUNT(*) AS counter
FROM lists
INNER JOIN inventory
ON (lists.food_id=inventory.food_id)
INNER JOIN (SELECT COUNT(*) AS num
FROM lists WHERE person_id=_pid
GROUP BY person_id) AS T
INNER JOIN stores ON (stores.id=store_id)
WHERE person_id=_pid
GROUP BY store_id
HAVING counter >= num;
Thanks for your time!
Edit SQL Fiddle with Data
If I were to solved the problem, I'll join the four tables with their linking column (specifically the foreign keys) then a subquery on the HAVING clause to count the number of items on the list for each person. Give this a try,
SET #personID := 1;
SELECT c.name
FROM Inventory a
INNER JOIN Foods b
ON a.food_id = b.id
INNER JOIN Stores c
ON a.store_id = c.id
INNER JOIN Lists d
ON d.food_id = b.id
WHERE d.person_id = #personID
GROUP BY c.name
HAVING COUNT(DISTINCT d.food_id) =
(
SELECT COUNT(*)
FROM Lists
WHERE person_ID = #personID
)
SQLFiddle Demo
#JohnWoo: why DISTINCT?
Another one...
SET #pid=2;
SELECT store_id, name
FROM inventory
JOIN lists ON inventory.food_id=lists.food_id
JOIN stores ON store_id=stores.id
WHERE person_id=#pid
GROUP BY store_id
HAVING COUNT(*)=(
SELECT COUNT(*)
FROM lists
WHERE person_id=#pid
);