Question

我有一个名为ngAfterViewInit() { postscribe('#adv', `<script type="text/javascript" language="javascript"> var aax_size='728x90'; var aax_pubname = 'XXXXXXXX'; var aax_src='302'; </script> <script type="text/javascript" language="javascript" src="http://c.amazon-adsystem.com/aax2/assoc.js"></script>`);}的postgres 9.6表，其中一个名为selected_media的列设置为_type或book。

我想在1行中选择每种类型的movie，如下所示：

COUNT

要做到这一点，我有这个问题：

25 | 715

问题是2折：

如果该列中的总和恰好为0（未选中），我希望每列都显示该<_>的总计数。这是因为UI / UX声明＆＃34;选择0本书或电影与选择所有书籍或＃34; 相同。
它需要很快，这个表中会有数百万行

Answer 1

您可以将COUNT与FILTER子句一起使用：

SELECT 
COUNT(*) FILTER (WHERE _type = 'book') AS books_count,
COUNT(*) FILTER (WHERE _type = 'movie') AS movies_count
FROM selected_media
WHERE subscriber_id = $1;

更多信息here。

<小时/> 的修改

使用嵌套子查询来满足您的第一需求：

SELECT
    CASE books_count WHEN 0 THEN (SELECT COUNT(*) FROM selected_media WHERE _TYPE = 'book') ELSE books_count END AS books_count_final,
    CASE movies_count WHEN 0 THEN (SELECT COUNT(*) FROM selected_media WHERE _TYPE = 'movie') ELSE movies_count END AS movies_count_final   
FROM 
    (
    SELECT 
        COUNT(*) FILTER (WHERE _type = 'book') AS books_count,
        COUNT(*) FILTER (WHERE _type = 'movie') AS movies_count
    FROM 
        selected_media
    WHERE 
        subscriber_id = $1
    ) AS sub_query

或使用CTE：

WITH selected_media_sub AS (
    SELECT 
        COUNT(*) FILTER (WHERE _type = 'book') AS books_count,
        COUNT(*) FILTER (WHERE _type = 'movie') AS movies_count
    FROM 
        selected_media
    WHERE 
        subscriber_id = $1
 )

SELECT
    CASE books_count WHEN 0 THEN (SELECT COUNT(*) FROM selected_media WHERE _TYPE = 'book') ELSE books_count END AS books_count_final,
    CASE movies_count WHEN 0 THEN (SELECT COUNT(*) FROM selected_media WHERE _TYPE = 'movie') ELSE movies_count END AS movies_count_final   
FROM selected_media_sub;

顺便说一句，如果您只需要一个非零计数，您可以执行以下操作：

SELECT 
    COALESCE(NULLIF(COUNT(*) FILTER (WHERE _type = 'book'), 0), 1) AS books_count,
    COALESCE(NULLIF(COUNT(*) FILTER (WHERE _type = 'movie'), 0), 1) AS movies_count
FROM 
    selected_media
WHERE 
    subscriber_id = $1

PG：如果结果为0，如何显示此查询的总计数

1 个答案: