查询以使用 GROUP_CONCAT 拆分偶数和奇数

Question

I have a query that finds housenumbers per street in a specific postcode with four numbers:

SELECT *,
    GROUP_CONCAT(DISTINCT CAST(housenumber AS int) ORDER BY housenumber ASC) AS housenumbers
FROM streets
WHERE postcode LIKE '3031%'
GROUP BY street
ORDER BY lat,lon

This is the result of the groupcatted housenumbers.

491,492,493,500,501,502,503,504,505,506,507,508,50

I would like to split the result, over two columns, in evenhousenumber and oddhousenumbers. I tried MOD and %2 , but both require a WHERE and it's not possible to use the WHERE in the groupcat function, I noticed.

How can I split the result, over even and odd numbers?

Answer 1

You could use CASE expression:

SELECT street
 ,GROUP_CONCAT(DISTINCT CASE WHEN MOD(CAST(housenumber AS int),2) = 0 THEN CAST(housenumber AS int) END ORDER BY housenumber ASC) AS housenumbers_even
 ,GROUP_CONCAT(DISTINCT CASE WHEN MOD(CAST(housenumber AS int),2) = 1 THEN CAST(housenumber AS int) END ORDER BY housenumber ASC) AS housenumbers_odd
FROM streets
WHERE postcode LIKE '3031%'
GROUP BY street
ORDER BY lat,lon;

It works because GROUP_CONCAT skips NULL values.

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Also SELECT * ... GROUP BY street is not safe. Related: Group by clause in mySQL and postgreSQL, why the error in postgreSQL?