Slow SQL view using several subqueries - sql

Question

There is probably a much better way to create these views. I have limited SQL experience so this is the way I designed it, I am hoping some of you SQL gurus can point me in a more efficient direction.
I essentially have 3 tables (sometimes 4) in my view, here is the essential structure:
Table USER
USER_ID | EMAIL | PASSWORD | CREATED_DATE
(Indexes: USER_ID)
Table USER_META
ID | USER_ID | NAME | VALUE
(Indexes: ID,USER_ID,NAME)
Table USER_SCORES
ID | USER_ID | GAME_ID | SCORE | CREATED_DATE
(Indexes: ID,USER_ID)
All the tables use the first ID column as an auto-increment primary key.
The second table "USER_META" is where I keep all the contact info and other misc. Primarily it is first_name,last_name, street,city, etc. - Depending on the user this could be 4 items or 140, which is why I use this table instead of having 150 columns in my USER table.
For reports, searching and editing I need about 20 values from USER_META, so I have views that look like this:
View V_USR_META
select USER_ID,EMAIL,
(select VALUE from USER_META
where NAME = 'FIRST_NAME' and USER_ID = u.USER_ID) as first_name,
(select VALUE from USER_META
where NAME = 'LAST_NAME' and USER_ID = u.USER_ID) as last_name,
(select VALUE from USER_META
where NAME = 'CITY' and USER_ID = u.USER_ID) as city,
(select VALUE from USER_META
where NAME = 'STATE' and USER_ID = u.USER_ID) as state,
(select VALUE from USER_META
where NAME = 'ZIP' and USER_ID = u.USER_ID) as zip,
/* 10 more selects for different meta values here */
(select max(SCORE) from USER_SCORES
where USER_ID = u.USER_ID) as high_score,
(select top (1) CREATED_DATE from USER_SCORES
where USER_ID = u.USER_ID
order by id desc) as last_game
from USER u
This get's pretty slow, and there are actually many more sub queries, this is just to illustrate the query. I also have to query a few other tables to get misc. info about the user.
I use the view when searching for a user, searches use name or userid or email or score, etc. I also use it to populate the user information screen when I present all the data in one place.
So - Is there a better way to write the view?

Answer 1

An alternative to all of those correlated subqueries would be to use max with case:
select u.USER_ID,
u.EMAIL,
max(case when um.name = 'FIRST_NAME' then um.value end) first_name,
max(case when um.name = 'LAST_NAME' then um.value end) last_name
...
from USER u
left join USER_META um
on u.user_id = um.user_id
group by u.user_id, u.email
Then you could add the user_scores results:
select u.USER_ID,
u.EMAIL,
max(case when um.name = 'FIRST_NAME' then um.value end) first_name,
max(case when um.name = 'LAST_NAME' then um.value end) last_name
...,
max(us.score) maxscore,
max(us.created_date) maxcreateddate
from USER u
left join USER_META um
on u.user_id = um.user_id
left join USER_SCORES us
on u.user_id = us.user_id
group by u.user_id, u.email

Answer 2

WITH Meta AS (
SELECT USER_ID
,FIRST_NAME
,LAST_NAME
,CITY
,STATE
,ZIP
FROM USER_META
PIVOT (
MAX(VALUE) FOR NAME IN (FIRST_NAME, LAST_NAME, CITY, STATE, ZIP)
) AS p
)
,MaxScores AS (
SELECT USER_ID
,MAX(SCORE) AS Score
FROM USER_SCORES
GROUP BY USER_ID
)
,LastGames AS (
SELECT USER_ID
,MAX(CREATED_DATE) AS GameDate
FROM USER_SCORES
GROUP BY USER_ID
)
SELECT USER.USER_ID
,USER.EMAIL
,Meta.FIRST_NAME
,Meta.LAST_NAME
,Meta.CITY
,Meta.STATE
,Meta.ZIP
,MaxScores.Score
,LastGames.GameDate
FROM USER
INNER JOIN Meta
ON USER.USER_ID = Meta.USER_ID
LEFT JOIN MaxScores
ON USER.USER_ID = MaxScores.USER_ID
LEFT JOIN LastGames
ON USER.USER_ID = LastGames.USER_ID