create temporary table classname
select 1 as cid, '小一班' as cid_name
union all select 2, '小二班'
union all select 3, '小三班'
union all select 4, '中一班'
union all select 5, '中二班'
union all select 6, '中三班'
union all select 7, '大一班'
union all select 8, '大二班';
create temporary table temp2
select 1 as sid, '張一' as sid_name, 2 as cid
union all select 2, '張二', 1
union all select 3, '張三', 1
union all select 4, '張四', 3
union all select 5, '張五', 2
union all select 6, '張六', 5
union all select 7, '張七', 6
union all select 8, '張八', 6;
MYSQL 統計每個班有多少個學生
uj5u.com熱心網友回復：
select cid,cid_name,(select count(*) from temp2 where cid=classname.cid)
from classname
uj5u.com熱心網友回復：
select a.cid_name ,count(*) c from classname a inner join temp2 b on a.cid=b.cidgroup by a.cid,a.cid_name
uj5u.com熱心網友回復：
最好不要用相關子查詢，每條記錄都執行一次子查詢，效率相當慢uj5u.com熱心網友回復：
如果為0的也要統計，那用 ：select a.cid_name ,count(b.cid) c from classname a left join temp2 b on a.cid=b.cid
group by a.cid,a.cid_name
uj5u.com熱心網友回復：
Select Select Sid ,count (1) num from temp2 group by sid轉載請註明出處，本文鏈接：https://www.uj5u.com/shujuku/30054.html
標籤：MySQL
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