如何在此查询中包含等于 0 的计数？答案

【问题标题】：How to include count equal to 0 on this query?如何在此查询中包含等于 0 的计数？
【发布时间】：2012-11-27 13:25:08
【问题描述】：

我的查询

select state,count(*) from crm_lead group by state;

state   count
done    794
open    560
pending 3
draft   8
cancel  1

但有时我的表中没有“取消”任务

state   count
done    794
open    560
pending 4
draft   8

我想在结果中包含 count = 0，最好的查询是什么？

【问题讨论】：

你有另一个包含所有州名的表吗？

标签： sql postgresql postgresql-9.1

【解决方案1】：

SELECT  a.STATE , 
        COALESCE(b.count, 0) AS Count
FROM 
    (
        SELECT 'done' AS STATE
        UNION
        SELECT 'open' AS STATE
        UNION
        SELECT 'pending' AS STATE
        UNION
        SELECT 'draft' AS STATE
        UNION
        SELECT 'cancel' AS STATE
    ) a LEFT JOIN 
    (
        SELECT  STATE , 
                count(*) AS count
        FROM    crm_lead
        GROUP BY STATE
    ) b ON a.STATE = b.STATE

【讨论】：

从行组成一个集合而不介意重复使用UNION ALL。不过，只有五行并不重要。

【解决方案2】：

如果您只想确保取消在列表中，您也可以这样做：

select coalesce(t.state, const.state) as state, coalesce(t.cnt, const.cnt) as cnt
from (select state, count(*) as cnt
      from crm_lead
      group by state
     ) t full outer join
     (select 'cancel' as state, 0 as cnt
     ) const
     on t.state = const.state

如果状态列表很长，或者您只想确保包含一个特定值，这可能会很方便。

【讨论】：

【解决方案3】：

VALUES 表达式更简单：

SELECT a.state, COALESCE(b.ct, 0) AS ct
FROM (VALUES('done'), ('open'), ('pending'), ('draft'), ('cancel')) a (state)
LEFT JOIN (
   SELECT state, count(*) AS ct
   FROM   crm_lead
   GROUP  BY state
 ) b USING (state);

【讨论】：

【解决方案4】：

$jsonb = array();
foreach($em as $k => $v) {  
    $q = "
        SELECT  a.STATE , 
        COALESCE(b.count, 0) AS Count
    FROM 
    (
        SELECT 'done' AS STATE
        UNION
        SELECT 'open' AS STATE
        UNION
        SELECT 'pending' AS STATE
        UNION
        SELECT 'draft' AS STATE
        UNION
        SELECT 'cancel' AS STATE
    ) a LEFT JOIN 
    (
        SELECT  STATE , 
                count(*) AS count
        FROM    crm_lead
        WHERE (create_date, create_date) OVERLAPS ('2012-{$nn}-01'::DATE, '2012-{$nn}-{$num}'::DATE)
        GROUP BY STATE
    ) b ON a.STATE = b.STATE
        ";
        $result = retrieve($q);

        $jsona = array();
        $values = array();
        $ev = array();
        foreach($result as $key => $val) {
            $ev[] = $val['count'];
        }

    $jsonb[] = array("label" => $v,"values" =>$ev);
}

$jsona[] = array("label" => array(done,open,pending,draft,cancel),"values" => $jsonb);

这是一个完整的代码，用于构造要返回给 JavaScript 的 JSON 对象。附言。这段代码包含了一些不重要的自定义函数，你可能会猜到它们的值。

【讨论】：