你的字段别名和你的表别名重复了
select count(a.ka_id) as n ,count(b.Ka_id) as m,c.Ka_Name from table1 a,table2 b,table3 c
where a.Ka_id=c.Ka_id and b.Ka_id=c.Ka_id
group by c.Ka_Name
select count(a.ka_id) as n ,count(b.Ka_id) as m,c.Ka_Name from table1 a,table2 b,table3 c
where a.Ka_id=c.Ka_id and b.Ka_id=c.Ka_id
group by c.Ka_Name
where a.Ka_id=c.Ka_id and b.Ka_id=c.Ka_id
group by c.Ka_Name
你這樣寫 根本沒意義吧?因為 你這樣得出的count(a.ka_id) 和count(b.ka_id)的結果一定是相同的
原因我是這樣認為的:我認為查詢"相當於"是把我們要的數據先放在一個虛表中,查詢完畢後自動釋放掉
對同一個表,相同一個條件,查詢count應該都是一樣的就象count(1)=count(2)=count(a.ka_id)=count(b.ka_id)