I have two tables like below,
mysql> select * from Books ;
+----+------+------------+----------+----------+
| id | name | author_name| category | category2|
+----+------+------------+----------+----------+
| 1 | 1 | Steve | CT001 | CT003 |
| 2 | 2 | John | CT002 | CT002 |
| 3 | 3 | Larry | CT003 | CT002 |
| 4 | 3 | Michael | CT004 | CT004 |
| 5 | NULL | Steven | CT005 | CT005 |
+----+------+------------+----------+----------+
mysql> select * from Codemst ;
+----+------+------------+
| id | code | name |
+----+------+------------+
| 1 | CT001| fiction |
| 2 | CT002| category1 |
| 3 | CT003| etc |
| 4 | CT004| etc2 |
| 5 | CT005| etc3 |
+----+------+------------+
I want to get human readable category name when I query like "select * from Books;"
If there was only one category in the Books table, I think I can use "Join" but, in this case what can I do?
select * from Books b
Inner Join Codemst c1 on b.category = c1.code
inner join codemst c2 on b.category2 = c2.code;
c1.name will hold the readable category, and c2.name the readable category2
Related
I have two MySQL tables (table_a and table_b) and a join table (table_c).
Table Structures:
table_a:
__________________
| table_a: |
|----------------|
| id |
| result_column |
------------------
table_b:
__________________
| table_b: |
|----------------|
| id |
| name |
------------------
table_c:
__________________
| table_c: |
|----------------|
| id |
| table_a_id |
| table_b_id |
------------------
My Goal:
I want to find a query that will:
Iterate over every table_a record and get the table_a.id value
Find any records in table_c which have a matching table_c.table_a_id value
For each matching record in table_c get the table_c.table_b_id value
Find the record in table_b which has a matching table_b.id value
For that matching record in table_b get the table_b.name value
In table_a, concatenate each matched name value into the corresponding table_a.result_column
Example:
Before the Query:
_______________________ _________________________________ ________________
| table_a: | | table_c: | | table_b: |
|---------------------| |-------------------------------| |--------------|
| id | result_column | | id | table_a_id | table_b_id | | id | name |
|-----|---------------| |-----|------------|------------| |-----|--------|
| 1 | | | 1 | 1 | 3 | | 1 | Kevin |
| 2 | | | 2 | 1 | 4 | | 2 | Jesse |
| 3 | | | 3 | 2 | 2 | | 3 | Karen |
----------------------- | 4 | 3 | 1 | | 4 | Tim |
| 5 | 3 | 5 | | 5 | Lauren |
--------------------------------- ----------------
After the Query:
_______________________ _________________________________ ________________
| table_a: | | table_c: | | table_b: |
|---------------------| |-------------------------------| |--------------|
| id | result_column | | id | table_a_id | table_b_id | | id | name |
|-----|---------------| |-----|------------|------------| |-----|--------|
| 1 | Karen, Tim | | 1 | 1 | 3 | | 1 | Kevin |
| 2 | Jesse | | 2 | 1 | 4 | | 2 | Jesse |
| 3 | Kevin, Lauren | | 3 | 2 | 2 | | 3 | Karen |
----------------------- | 4 | 3 | 1 | | 4 | Tim |
| 5 | 3 | 5 | | 5 | Lauren |
--------------------------------- ----------------
For absolute clarity, I understand that this is incredibly bad practice within a relational data-table. This is as far from normalization as one can get. I would never design a database like this. I was tasked with creating a custom column with a list of values purely for a business case.
The query you seem to want is:
select c.table_a_id, group_concat(b.name separator ', ')
from c join
b
on c.table_b_id = b.id
group by c.table_a_id;
If you actually want to update a, you can put this into an update statement:
update a join
(select c.table_a_id, group_concat(b.name separator ', ') as names
from c join
b
on c.table_b_id = b.id
group by c.table_a_id
) cb
on cb.table_a_id = a.id
set result_column = cb.names
Previous answer is close; but you also required that you only want the records matched in table C that are in A.
The first query does not meet this requirement; but the update statement does, as it will only update records in table A, if the id matches the table_a_id value pulled from table C.
Given what you said you wished for the end result, the update statement above would work.
If you wish to be explicit in your logic, just add a join from table A to table C.
select a.id, group_concat(b.name separator ', ')
from a
join c ON (a.id = c.table_a_id)
join b ON (c.table_b_id = b.id)
group by a.id;
this is my first time posting here. I don't seem to find the answer to my problem.
So... I'm arranging a DB for a school project, a cookbook that only shows recipes that can be made with existing elements from the "shelf".
These ingredients have to have an exact ingredients match.
user:
+---------------+------+----------+----------+
| email | name | lastname | password |
+---------------+------+----------+----------+
| pal#mail.com | John | Potato | password |
| they#mail.com | Mary | Carrot | password |
+---------------+------+----------+----------+
shelf:
+---------+------------+---------------+
| shelfID | ingredient | user |
+---------+------------+---------------+
| 1 | 1 | pal#mail.com |
| 2 | 2 | pal#mail.com |
| 3 | 3 | pal#mail.com |
| 4 | 4 | pal#mail.com |
| 5 | 10 | they#mail.com |
| 6 | 12 | they#mail.com |
+---------+------------+---------------+
This is my recipe_ingredient relationship table
recipe_ingredient:
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 1 | 1 |
| 1 | 2 |
| 1 | 4 |
| 1 | 10 |
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 2 | 4 |
| 3 | 2 |
| 3 | 3 |
| 3 | 15 |
+--------+------------+
I've tried this query:
SELECT
rec_ing.recipe, shf.ingredient, shf.user
FROM
recipes_ingredients AS rec_ing
INNER JOIN
shelf AS shf ON rec_ing.ingredient = shf.ingredient
INNER JOIN
users AS usr ON shf.user = usr.email
WHERE
usr.email = 'pal#mail.com'
that returns this table:
+--------+------------+--------------+
| recipe | ingredient | user |
+--------+------------+--------------+
| 1 | 1 | pal#mail.com |
| 1 | 2 | pal#mail.com |
| 1 | 4 | pal#mail.com |
| 2 | 1 | pal#mail.com |
| 2 | 2 | pal#mail.com |
| 2 | 3 | pal#mail.com |
| 2 | 4 | pal#mail.com |
| 3 | 2 | pal#mail.com |
| 3 | 3 | pal#mail.com |
+--------+------------+--------------+
Although it's true that the Recipe 1 contains ingredients from my shelf, it's also missing Ingredient 10
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 1 | 1 |
| 1 | 2 |
| 1 | 4 |
| 1 | 10 |
| ... | ... |
+--------+------------+
I'm trying to only get this kind of result set.
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 2 | 4 |
+--------+------------+
Because Recipe 2 contains all elements from my shelf
I have been going around all day with this problem ... What could be missing?
This is a bit tricky, because you need to aggregate your current query by recipe, but you also need the original query to get back the full records. Sadly, MySQL does not support common table exprrssions or other features which could give us a less verbose query.
SELECT
rec_ing.recipe,
shf.ingredient,
shf.user
FROM recipes_ingredients AS rec_ing
INNER JOIN shelf AS shf
ON rec_ing.ingredient = shf.ingredient
INNER JOIN users AS usr
ON shf.user = usr.email
INNER JOIN
(
SELECT rec_ing.recipe
FROM recipes_ingredients AS rec_ing
INNER JOIN shelf AS shf
ON rec_ing.ingredient = shf.ingredient
LEFT JOIN users AS usr
ON shf.user = usr.email
WHERE
usr.email = 'pal#mail.com'
GROUP BY rec_ing.recipe
HAVING COUNT(usr.email) = COUNT(*)
) t
ON rec_ing.recipe = t.recipe
WHERE
usr.email = 'pal#mail.com'
The basic strategy here is to just do one additional join to a subquery which identifies all recipes where every ingredient belongs to a given user. The critical part is the following:
HAVING COUNT(usr.email) = COUNT(*)
This checks that the total number of rows for a given recipe matches the number of rows which have been assigned to a given user.
I have a question and answer website like stackoverflow. Here is the structure of some tables:
-- {superfluous} means some other columns which are not related to this question
// q&a
+----+-----------------+--------------------------+------+-----------+-----------+
| id | title | body | type | related | author_id |
+----+-----------------+--------------------------+------+-----------+-----------+
| 1 | How can I ... | I'm trying to make ... | q | NULL | 3 |
| 2 | | You can do that by ... | a | 1 | 1 |
| 3 | Why should I .. | I'm wonder, why ... | q | NULL | 1 |
| 4 | | First of all you ... | a | 1 | 2 |
| 5 | | Because that thing ... | a | 3 | 2 |
+----+-----------------+--------------------------+------+-----------+-----------+
// users
+----+--------+-----------------+
| id | name | {superfluous} |
+----+--------+-----------------+
| 1 | Jack | |
| 2 | Peter | |
| 3 | John | |
+----+--------+-----------------+
// votes
+----+----------+-----------+-------+-----------------+
| id | user_id | post_id | value | {superfluous} |
+----+----------+-----------+-------+-----------------+
| 1 | 3 | 4 | 1 | |
| 2 | 1 | 1 | -1 | |
| 3 | 2 | 1 | 1 | |
| 4 | 3 | 2 | -1 | |
| 5 | 1 | 4 | 1 | |
| 6 | 3 | 5 | -1 | |
+----+--------+-------------+-------+-----------------+
// tags
+----+------------+-----------------+
| id | name | {superfluous} |
+----+------------+-----------------+
| 1 | PHP | |
| 2 | SQL | |
| 3 | MySQL | |
| 4 | HTML | |
| 5 | CSS | |
| 6 | C# | |
+----+------------+-----------------+
// q&aTag
+-------+--------+
| q&aid | tag_id |
+-------+--------+
| 1 | 1 |
| 1 | 4 |
| 3 | 5 |
| 3 | 4 |
| 4 | 6 |
+-------+--------+
Now I need to find top users in a specific tag. For example, I need to find Peter as top user in PHP tag. Because his answer for question1 (which has PHP tag) has earned 2 upvotes. Is doing that possible?
Try this:
select q1.title, u.id, u.name, sum(v.value) total from `q&a` q1
left join `q&atag` qt ON q1.id = qt.`q&aid`
inner join tags t ON qt.tag_id = t.id
left join `q&a` q2 ON q2.related = q1.id
left join users u ON q2.author_id = u.id
left join votes v ON v.post_id = q2.id
where t.name = 'PHP'
group by q1.id, u.id
and here is a simple divided solution:
Let us divide it into sub queries:
get the id of the tag you will search for: select id from tags where name = 'PHP'
get the questions with this tag: select 'q&aid' from 'q&aTag' where tag_id = 1.
get the ids of answers for that question: select id, author_id fromq&awhere related in (2.)
get the final query: select user_id, sum(value) from votes where post_id in (3.) group by user_id
Now combining them all give the result:
select user_id, sum(`value`) total from votes
where post_id in (
select id from `q&a` where related in (
select `q&aid` from `q&aTag` where tag_id IN (
select id from tags where name = 'PHP'
)
)
)
group by user_id
you can add this at the end if you want only one record:
order by total desc limit 1
This question is a little long so that it would be clear, thanks in advance!
Introduction
I currently have 3 tables using a many-to-many relationship. I need to query all 3 tables and combine them into 1 table.
Problem
I have tried this query:
SELECT * FROM `login` LEFT JOIN membership ON login.id = membership.login_id UNION SELECT * FROM `login` RIGHT JOIN membership ON login.id = membership.login_id
And it returns:
+----+------+----------+
| id | name | group_id |
+----+------+----------+
| 1 | Tom | 6 |
| 2 | John | 8 |
| 3 | Jane | 4 |
+----+------+----------+
Question
I need it to also include the group_name. This is my desired output:
+----+------+----------+------------+
| id | name | group_id | group_name |
+----+------+----------+------------+
| 1 | Tom | 6 | Red |
| 2 | John | 8 | Brown |
| 3 | Jane | 4 | Purple |
+----+------+----------+------------+
Tables
login Table
A list of all users with auto-increment id
+----+------+
| id | name |
+----+------+
| 1 | Tom |
| 2 | John |
| 3 | Jane |
+----+------+
group Table
A list of all groups with the group_id and group_name
+----------+------------+
| group_id | group_name |
+----------+------------+
| 1 | Green |
| 2 | Blue |
| 3 | Yellow |
| 4 | Purple |
| 5 | Orange |
| 6 | Red |
| 7 | Pink |
| 8 | Brown |
+----------+------------+
membership Table
Stores information on which user belongs to which group
+----------+----------+
| login_id | group_id |
+----------+----------+
| 1 | 6 |
| 2 | 8 |
| 3 | 4 |
+----------+----------+
Join the group table as well and select the required fields from the tables.
SELECT l.id,l.name,m.group_id,g.group_name
FROM `login` l
LEFT JOIN `membership` m ON l.id = m.login_id
LEFT JOIN `group` g on g.group_id = m.group_id
Try this... :)
SELECT
`login`.`id`,
`login`.`name`,
`group`.`group_id`,
`group`.`group_name`
FROM
`membership`
INNER JOIN `login` ON (`membership`.`login_id` = `login`.`id`)
INNER JOIN `group` ON (`membership`.`group_id` = `group`.`group_id`)
Here is my query and it's not showing the 3rd row even though the tables contents match.
SELECT shopcategory_idcategory_name
FROM shopcategory
INNER JOIN category ON shopcategory_id=category_id;
Result:
================================================================
| shopcategory_id | shopcategory_shopid | category_name |
================================================================
| 1 | 1 | Gadgets |
| 2 | 2 | Analog Device |
================================================================
Here is my query that shows it has 3 rows
SELECT * FROM shopcategory;
Result:
===================================================================
| shopcategory_id | shopcategory_shopid | shopcategory_categoryid |
===================================================================
| 1 | 1 | 1 |
| 2 | 2 | 2 |
| 3 | 3 | 3 |
===================================================================
EDIT: Query for my category table
SELECT * category;
Result:
==============================================
| category_id | category_name |
==============================================
| 1 | Gadgets |
| 2 | Analog Device |
| 3 | Beauty |
| 4 | Keyboard |
| 5 | Instruments |
| 6 | Monitor |
| 7 | Chairs |
==============================================
You should use LEFT JOIN here instead and add aliases for tables that you are joining on, like this:
SELECT
tableName1.shopcategory_id,
tableName1.category_name,
tableName2.category_id
FROM
tableName1 as tb1
LEFT JOIN
tableName2 AS tb2
ON
tb1.shopcategory_id = tb2.category_id
GROUP BY
tb1.shopcategory_id;