I have the following table:
att_id | user_id | att_name | att_value
1 | 202 | first_name| Cris
2 | 202 | last_name | Williams
3 | 202 | email | cwill122@yahoo.com
I want to return a table like:
202 | Chris | Wiliams | cwill122@yaoo
You can do conditional aggregation. This is the cannonical way to pivot a dataset:
select
user_id,
max(case when att_name = 'first_name' then att_value end) first_name,
max(case when att_name = 'last_name' then att_value end) last_name,
max(case when att_name = 'email' then att_value end) email
from mytable
group by user_id
我的建议是将字段att_name att_value放在另一个表中并进行连接
You'll need to self-join the table, giving it aliases.
SELECT t1.att_value, t2.att_value, t3.att_value FROM [tablename] t1 JOIN [tablename] t2 ON t1.att_id = t2.att_id JOIN [tablename] t3 ON t3.att_id = t1.att_id WHERE user_id = 202
Store the user_id in a variable(say uid) and then take the first_name, last_name, email of uid in other variables. Then u can insert them into a new table. Or u can use join to do the work and create a view to use in in future.
You can use a PIVOT(MSSQL/TSQL).
WITH PivotData AS
(
SELECT user_id, att_name, att_value FROM dbo.AttTable
)
SELECT user_id, first_name, last_name, email
FROM PivotData
PIVOT(MAX(att_value) FOR att_name IN(first_name, last_name, email)) AS P;
Test data
CREATE TABLE dbo.AttTable
(
att_id INT NOT NULL,
user_id INT NOT NULL,
att_name VARCHAR(50) NOT NULL,
att_value VARCHAR(50) NOT NULL,
PRIMARY KEY (att_id, user_id)
);
INSERT INTO dbo.AttTable
(att_id, user_id, att_name, att_value)
VALUES
(1, 202, 'first_name', 'Cris'),
(2, 202, 'last_name', 'Williams'),
(3, 202, 'email', 'cwill122@yahoo.com')
select
I.user_id,A.fname, B.lname, C.email
from
(select distinct user_id from AttTable) I
left join
(select user_id, att_value as fname from AttTable where att_name = 'first_name') A
on I.user_id = A.user_ID
left join
(select user_id, att_value as lname from AttTable where att_name = 'last_name') B
on I.user_id = B.user_id
left join
(select user_id, att_value as email from AttTable where att_name = 'email') C
on I.user_id = C.user_id
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