如何格式</p> <p>在一個查詢中選擇與計數和限制的Postgres數據

Question

數據

PostgreSQL的表的表名是TBL1 TBL1

id -- RCODE -- CCODE -- LDATA 
1  123  50  p1 
2  124  51  p2 
3  126  50  p3 

....... ................ ......... ..... 。

23  116  56  p3 
24  126  50  p9 
25  126  50  p3 
26  136  56  p5 
27  126  50  p3 
28  146  52  p7 

我的問題是如何找到有RCODE =126

Answer 1

select count(*) as total 
from (
    select CCODE 
    from tbl1 
    where RCODE = 126 
    order by id desc 
    limit 7 
    ) s 
where CCODE = 50 

Answer 2

使用子查詢，生成一箇中間表a其中包含最後7所記載的CCODE =50從去年7個記錄的分貝計數據庫有RCODE = 126。然後在其上運行COUNTWHERE CCODE=50。查詢：

SELECT COUNT(*) 
FROM (
    SELECT CCODE 
    FROM tbl1 
    WHERE RCODE = 126 
    ORDER BY id DESC LIMIT 7 
) AS a 
WHERE CCODE = 50