How to include count equal to 0 on this query?

问题

My query

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

which return

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

but sometime when I have no 'cancel' task in my table

state   count
done    794
open    560
pending 4
draft   8

I would like to include count = 0 in the result, what is the best query ?

回答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

回答2:

You can also do this, if you only want to be sure that cancel is in the list:

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

This might be handy if the list of states is long or if you only want to be sure that one particular value is included.

回答3:

Simpler with a VALUES expression:

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);

回答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);

this is a completed code to contruct a JSON object to be returned to the JavaScript. ps. this code included some custom functions which are not important, you may guess the values of them.

来源：https://stackoverflow.com/questions/13576402/how-to-include-count-equal-to-0-on-this-query

标签

sql

postgresql

postgresql-9.1