問題描述

前提 oralce，mybatis現(xiàn)在有多張表 我現(xiàn)在需要統(tǒng)計(jì)每張表里面的信息的數(shù)量,也就是count(*)

我現(xiàn)在的方法是寫了多個(gè)方法 比如 mapper里：long selectCountA;long selectCountB;long selectCountC;

這樣的話，我要去數(shù)據(jù)庫(kù)里查三次。分別獲得3個(gè)數(shù)據(jù)我想能不能 寫一句sql語(yǔ)句 直接獲得三個(gè)值

求解？

。能給我一個(gè)oracle語(yǔ)句的嗎， 咋都是mysql。。

問題解答

select 'a' name, count(1)from tableAunionselect 'b' name, count(1)from tableBunionselect 'C' name, count(1)from tableC

采用多列的寫法

with temp_a as (select count(*) num from talbeA),temp_b as (select count(*) num from tableB),temp_c as (select count(*) num from tableC)select temp_a.num, temp_b.num, temp_c.num from dual;回答2：

select A.countA,B.countB from (select count(*) as countA from t_countA) as A ,(select count(*) as countB from t_countB) as B

這樣?

Mysql

Oracle在以上語(yǔ)句后面加 from dual

Mysql的select table_rows from information_schema.TABLES where table_schema in (’schema1’,’schema2’,’scheman’) and table_name in (’tableName1’,’tableName2’,’tableNameN’)相信 oralce也有類似的系統(tǒng)表