如何在 postgresql 中合並多個 select 語句？

Question

我剛開始學習如何編碼。 我想知道如何在一個查詢中組合多個 SELECT 語句。

SELECT count(*) AS "SENT" FROM message_items WHERE status = 'SENT';

SELECT count(*)  AS "NOT SENT" FROM message_items WHERE status = 'NOT SENT';

SELECT count(*) AS "INVALID NUMBER" FROM message_items WHERE status = 'INVALID NUMBER';

Answer 1

使用條件聚合：

SELECT
    COUNT(*) FILTER (WHERE status = 'SENT') AS "SENT",
    COUNT(*) FILTER (WHERE status = 'NOT SET') AS "NOT SENT",
    COUNT(*) FILTER (WHERE status = 'INVALID NUMBER') AS "INVALID NUMBER"
FROM message_items;

如果您想在整個表上生成計數，那么上面的方法是合適的。 相反，如果您想為每個其他列生成計數，則只需將該列添加到上面的 select 子句中，然后使用GROUP BY按該列聚合。

Answer 2

您可以使用GROUP BY

SELECT count(*), status FROM message_items GROUP BY status;