php - 为什么这两个 Count 返回相同的数字？

Question

$SQL = "SELECT pc.dist_id, pc.route, pc.types,
        COUNT( pc.types = '$type' ) total,
        COUNT( pc.types = '$type' AND pc.options = '1') callbacks

        FROM per_call pc
        WHERE pc.types = '$type'
        GROUP BY pc.dist_id, pc.route, pc.types
        ORDER BY pc.dist_id, pc.route";

简而言之，我想我是在问 COUNT 如何与 () 内的多个列一起使用。

Answer 1

Count 也可以工作:

SELECT pc.dist_id, pc.route, pc.types,
COUNT( CASE WHEN pc.types = '$type' THEN 1 END) total,
COUNT( CASE WHEN pc.types = '$type' AND pc.options = '1' THEN 1 END) callbacks

FROM per_call pc
WHERE pc.types = '$type'
GROUP BY pc.dist_id, pc.route, pc.types
ORDER BY pc.dist_id, pc.route

注意:它之所以有效，是因为 COUNT 返回非 NULL 值的数量，而 CASE 具有默认的 ELSE NULL ...