優化我的日志報告查詢

Question

我正在做一個日志報告，其中我編寫了一個查詢來從數據庫中獲取結果，但是它太慢了，結果來得很慢。 有人為我優化了它，還告訴我一些有關優化的鏈接。 查詢在這里：

select '$variable' as cell,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-01')) as jan,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-02')) as feb,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-03')) as mar,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-04')) as apr,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-05')) as may,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-06')) as jun,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-07')) as jul,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-08')) as aug,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-09')) as sep,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-10')) as oct,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-11')) as nov,
COALESCE(( SELECT count(distinct cellno) FROM smsreports s WHERE s.cellno = '$variable' AND fmonth = '2015-12')) as dec

優化此查詢以獲取結果，請記住我想要這里的月度結果。

Answer 1

您要進行條件聚合：

select '$variable' as cell,
        count(distinct case when fmonth = '2015-01' then cellno end) as jan,
        count(distinct case when fmonth = '2015-02' then cellno end) as feb,
        . . . 
        count(distinct case when fmonth = '2015-12' then cellno end) as dec
FROM smsreports s
WHERE s.cellno = '$variable';