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Re: Can't get my query to return wanted data




Hello Chris,

On 1/19/2018 12:50 AM, Chris Roy-Smith wrote:
Hi
I am running mysql 5.7.20 in ubuntu linux 17.10

I have 2 tables, member and status with contents like

member:
ident, 	given, 	surname
1	fred	jones
2	john	howard
3	henry	wales
4	jenny	brown

status:
ident	year
1	2017
2	2017
3	2017
4	2017
1	2018
3	2018

I want my query to return the name and ident from the member table for all
members that has not got an entry in status with year=2018

I have been working on the following query to achieve this, but it only
returns data when there is no `year` entries for a selected year.

select details.ident, given, surname from details left join status on
details.ident = status.ident where NOT EXISTS (select year from status
where (status.year = 2018) and (details.ident = status.ident) )


Thank you for looking at this.
regards, Chris Roy-Smith



try this...

SELECT
  d.ident, d.given, d.surname
FROM details d
LEFT JOIN (
  SELECT DISTINCT ident
  FROM status
  WHERE year=2018
) s
  ON s.ident = d.ident
WHERE
  s.ident is NULL;

How it works....
#
Start by building a list of unique `ident` values that match the condition you do NOT want to find. (you will see why in a moment)

LEFT JOIN that list to your list of members (with your list on the right side of the LEFT JOIN). Where that join's ON condition is satisfied, a value for the column s.ident will exist. Where it isn't satisfied, there will be a NULL value in s.ident.

Finally, filter the combination of the s and d tables (I'm referring to their aliases) to find all the rows where s.ident was not given a value because it did not satisfy the ON condition of your outer join.
#

Yours,
--
Shawn Green
MySQL Senior Principal Technical Support Engineer
Oracle USA, Inc. - Integrated Cloud Applications & Platform Services
Office: Blountville, TN

Become certified in MySQL! Visit https://www.mysql.com/certification/ for details.

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