查询以使用 GROUP_CONCAT 拆分偶数和奇数

Question

我有一个查询，可以在具有四个数字的特定邮政编码中查找每条街道的门牌号码：

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

这是 groupcatted 门牌号码的结果。

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

我想将结果分成两列，分别为evenhousenumber 和oddhousenumbers。我试过MODand %2，但都需要 aWHERE并且不可能WHERE在 groupcat 函数中使用 ，我注意到。

如何将结果拆分为偶数和奇数？

Answer 1

你可以使用CASE表达式：

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;

它有效，因为GROUP_CONCAT跳过NULL值。

也SELECT * ... GROUP BY street并不安全。相关：mySQL 和 postgreSQL 中的 Group by 子句，为什么 postgreSQL 中出现错误？