CODEWITHSUNDEEP
mysqlsql
ChrisG
ChrisG

Reputation: 289

WHERE condition across multiple rows

I have this table...

--------------------------------------
| user_id |  status   |  status_date |
--------------------------------------
|    1    |  Current  |  2012-08-01  |
|    1    |  Referral |  2012-03-14  |
|    2    |  Referral |  2012-04-23  |
|         |           |              |
--------------------------------------

How would I query to find a distinct user_id who has a referral date before 2012-06-30 AND either a current date of after 2012-06-30 or no current status record at all?

Database is MySQL.

Upvotes: 2

Views: 123

Answers (3)

Ray
Ray

Reputation: 41428

Avoid doing innner selects with MySQL. All versions up to and including 5.5 cannot optimize properly with them. Use JOINs: 

SELECT distinct t1.user_id 
  FROM tablename t1 
  LEFT JOIN tablename t2 on t1.user_id = t2.user_id AND t1.status != t2.status
  WHERE t1.status = 'Referral' 
        AND t1.status_date '2012-06-30' 
        AND ( (t2.status IS NULL) OR 
              (t2.status = 'Current' AND t2.status_date > '2012-06-30'));

Upvotes: 0

GarethD
GarethD

Reputation: 69769

You can do this using a LEFT JOIN:

SELECT  DISTINCT T.User_ID
FROM    T
        LEFT JOIN T T2
            ON t.User_ID = T2.User_ID
            AND t2.Status = 'Current'
WHERE   T.Status_Date < '20120630'
AND     T.Status = 'Referral'
AND     (t2.Status_Date > '20120630' OR t2.Status_date IS NULL)

Or, using GROUP BY with HAVING and COUNT(CASE ...)

SELECT  t.User_ID
FROM    T
GROUP BY t.user_ID
HAVING  COUNT(CASE WHEN t.Status = 'Referral' AND t.Status_Date < '20120630' THEN 1 END) > 0
AND (   COUNT(CASE WHEN t.Status = 'Current' AND t.Status_Date > '20120630' THEN 1 END) > 0
    OR  COUNT(CASE WHEN t.Status = 'Current' THEN 1 ELSE 0 END) = 0
    )

It will depend on your indexes and amount of data as to which performs better, I'd imagine in most cases it will be the former

Upvotes: 2

Lamak
Lamak

Reputation: 70638

This should do it:

SELECT DISTINCT user_id
FROM YourTable T
WHERE status = 'Referral' 
AND status_date < '2012-06-30'
AND NOT EXISTS (SELECT user_id FROM YourTable 
                WHERE user_id = T.user_id AND status = 'Current' 
                AND status_date < '2012-06-30')

Upvotes: 1

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