Selecting row data as columns - mysql

Question

I have a contacts table where contact_type_id means:
1- email2 - phone3 - skype
The example below shows 3 different users with different types of contacts.
First user has phone number and Skype. The second one has only email. The third one has all 3 types: email, phone number & Skype.
user_id contact_type_id value
1 2 353234
1 3 skypeLogin
2 1 example#mail.com
3 1 example2#mail.com
3 2 123345
3 3 skypeLogin2
Issue needed to be clarified
How can I select this data as the following table
user_id email phone skype
1 null 353234 skypeLogin
2 example#mail.com null null
3 example2#mail.com 123345 skypeLogin2

Answer 1

Pivot is what you're looking for. If you have an unknown number of contact_type_id's then google Dynamic Pivot - there are tons of examples on SO.
This is for SQL Server:
CREATE TABLE #Contacts
(
user_id INTEGER
,contact_type_id INTEGER
,value NVARCHAR(20)
);
INSERT INTO #Contacts
( user_id, contact_type_id, value )
VALUES
( 1, 2, '353234' ),
( 1, 3, 'skypeLogin' ),
( 2, 1, 'example#mail.com' ),
( 3, 1, 'example2#mail.com' ),
( 3, 2, '123345' ),
( 3, 3, 'skypeLogin2' );
SELECT
pvt.user_id
,pvt.[1] email
,pvt.[2] phone
,pvt.[3] skype
FROM
#Contacts
PIVOT( MAX(value) FOR contact_type_id IN ( [1], [2], [3] ) ) pvt;
user_id email phone skype
----------- -------------------- -------------------- --------------------
1 NULL 353234 skypeLogin
2 example#mail.com NULL NULL
3 example2#mail.com 123345 skypeLogin2
(3 row(s) affected)

Answer 2

If MySQL then use CASE WHEN along with GROUP BY
SELECT
user_id,
MAX(CASE WHEN contact_type_id = 1 THEN `value` END) AS email,
MAX(CASE WHEN contact_type_id = 2 THEN `value` END) AS phone,
MAX(CASE WHEN contact_type_id = 3 THEN `value` END) AS skype
FROM your_table
GROUP BY user_id
WORKING DEMO

Answer 3

This works on sql server and mysql. Note value should be escaped in sql server.
USE sandbox;
/*
create table users(user_id int,contact_type_id int, value varchar(20));
insert into users values
(1, 2, '353234'),
(1, 3, 'skypeLogin'),
(2, 1, 'example#mail.com'),
(3, 1, 'example2#mail.com'),
(3, 2, '123345'),
(3, 3, 'skypeLogin2');
*/
select user_id,
max(case when contact_type_id = 1 then value else '' end) as email,
max(case when contact_type_id = 2 then value else '' end) as tel,
max(case when contact_type_id = 3 then value else '' end) as skpe
from users
group by user_id;

Answer 4

One is Pivot table, other can be below logic:
Create 3 Tables :
1. With user_id and Value for only email i.e. where contact_type_id=1
2. With user_id and Value for only phone i.e. where contact_type_id=2
3. With user_id and Value for only skype i.e. where contact_type_id=3
4. Outer join the three tables.
Below code does the same:
Select A.user_id,A.value as email, B.value as Phone, C.Value as Skype
from contacts A
outer join contacts B
On A.User_id=B.User_ID and A.value=1 and B.value=2
outer join contacts C
On A.User_id=C.User_ID and C.Value=3