How to disregard a row in a returned MS Access query when all fields bar one are distinct - sql

Question

I'm trying to create a query on Access 2010 which only produces a single row per patient. There are a really small number of patients (each patient represented by
a unique nhs_number in the table n) who are listed as having 2 practices in the table pp and so two rows are generated for them. Is there a way I can arbitrarily select one of the practices and ignore the other?
This is the query:
SELECT DISTINCT
n.nhs_number,
IIF(ch.care_home_date>#2/1/1900#, "TRUE", "FALSE") AS care_home,
pp.practice
FROM (nhs_no_tbl AS n
LEFT JOIN patient_practice_tbl AS pp ON n.nhs_number = pp.nhs_number)
LEFT JOIN patient_care_home_tbl AS ch ON n.nhs_number = ch.nhs_number;
The tables the query is using contains data along these lines:
nhs_no_tbl:
|nhs_number|
| -------- |
|1 |
|2 |
|3 |
|4 |
patient_practice_tbl:
|nhs_number|practice|
| -------- | ------ |
|1 |GP_A |
|2 |GP_A |
|3 |GP_B |
|4 |GP_A |
|4 |GP_B |
patient_care_home_tbl:
|nhs_number|care_home_date|
| -------- | ------------ |
|1 |1/5/2000 |
|1 |1/10/2010 |
|4 |26/10/2017 |
At the end, I'd like the query to return the following:
|nhs_number|Care_home|practice|
| -------- | ------- | ------ |
|1 |TRUE |GP_A |
|2 |FALSE | |
|3 |FALSE | |
|4 |TRUE |GP_A [or GP_B] |

Answer 1

I've update the query with CTE,
;WITH cte1 AS ---select all results
(
SELECT DISTINCT nnt.nhs_number,
CASE WHEN pcht.care_home_date IS NULL
THEN 'FALSE'
ELSE 'TRUE'
END AS CareHome,
ppt.practice,
rank()OVER(PARTITION BY nnt.nhs_number ORDER BY ppt.practice) AS R
FROM #nhs_no_tbl nnt
LEFT JOIN #patient_practice_tbl ppt ON nnt.nhs_number = ppt.nhs_number
LEFT JOIN #patient_care_home_tbl pcht ON nnt.nhs_number = pcht.nhs_number
),
CTE2 AS ---choose who may have multiple pracices
(
SELECT nhs_number
FROM CTE1
WHERE R = 2
),
CTE3 AS --- combine GP_A and GP_B
(
SELECT t.nhs_number,STRING_AGG(val,',') AS Practices
FROM
(
SELECT DISTINCT val = cte1.practice, CTE1.nhs_number
FROM #nhs_no_tbl nnt
INNER JOIN CTE2 ON nnt.nhs_number = CTE2.nhs_number
INNER JOIN cte1 ON nnt.nhs_number = CTE1.nhs_number
) t
--RIGHT JOIN #nhs_no_tbl nnt ON t.nhs_number = nnt.nhs_number
GROUP BY t.nhs_number
)
SELECT cte1.nhs_number,cte1.carehome,cte1.practice, cte3.Practices
FROM CTE1
LEFT JOIN cte3 ON cte1.nhs_number = CTE3.nhs_number
The result would be
then next you could store the result into a temp table and update temp table where practices is not null.