MySQL – SQL-Abfragestatistiken

Question

![Ich muss das U und A zählen, das jeder Layer-ID entspricht. Zum Beispiel
HYD_NET_LN U 5 A 10
HYD_VAL_PT U 8 A 25
Wie schreibt man
][1]

Answer 1

简单点，不知道这样可不可以。
SELECT layerid,ChangeMold,COUNT(ChangeMold) FROM table_name
GROUP BY layerid,ChangeMold

Answer 2

select count(*),layid,changeMold from tbl group by layid,changeMold

Answer 3

SELECT 
layerid,
sum(case when changeMold='U' then 1 else 0 end) changeMold_U,
sum(case when changeMold='A' then 1 else 0 end) changeMold_A
FROM table_name 
GROUP BY layerid;

Answer 4

如果 要 统计这种大文件 的话 。还是都查出来 然后再处理数组方便点（sql比较弱 ）

Answer 5

select layerid,changeMold,count(*) as num from TABLE where layerid in (select layerid from TABLE group by layerid) group by changeMold; 这条sql的性能很不好