select count (1)V_COUNT := 0;SELECT COUNT(1) INTO V_COUNT FROM CUST WHERE CUST_ID = ARG_CUST_ID;IF V_COUNT = 0 THEN我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思?

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select count (1)V_COUNT := 0;SELECT COUNT(1) INTO V_COUNT FROM CUST WHERE CUST_ID = ARG_CUST_ID;IF V_COUNT = 0 THEN我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思?
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select count (1)V_COUNT := 0;SELECT COUNT(1) INTO V_COUNT FROM CUST WHERE CUST_ID = ARG_CUST_ID;IF V_COUNT = 0 THEN我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思?
select count (1)
V_COUNT := 0;
SELECT COUNT(1) INTO V_COUNT
FROM CUST
WHERE CUST_ID = ARG_CUST_ID;
IF V_COUNT = 0 THEN
我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思?

select count (1)V_COUNT := 0;SELECT COUNT(1) INTO V_COUNT FROM CUST WHERE CUST_ID = ARG_CUST_ID;IF V_COUNT = 0 THEN我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思?
count(1),其实就是计算一共有多少符合条件的行.
1并不是表示第一个字段,而是表示一个固定值.
其实就可以想成表中有这么一个字段,这个字段就是固定值1,count(1),就是计算一共有多少个1.
同理,count(2),也可以,得到的值完全一样,count('x'),count('y')都是可以的.一样的理解方式.在你这个语句理都可以使用,返回的值完全是一样的.就是计数.
count(*),执行时会把星号翻译成字段的具体名字,效果也是一样的,不过多了一个翻译的动作,比固定值的方式效率稍微低一些.

select count(1) from emp select count和select count的区别 select Count(0) from MbrMember where 1=1Count(0)where 1=1 select count(*)count 什么意思和select * 有什么区别 select count(*) from 怎么使用 and select 4718 fromselect count select count (1)V_COUNT := 0;SELECT COUNT(1) INTO V_COUNT FROM CUST WHERE CUST_ID = ARG_CUST_ID;IF V_COUNT = 0 THEN我是个初学者,今有如上这么一段程序,里面select count(1)是什么意思? select id from (select id from pedigree group by number having count(name)>1)as a; 为啥用as a 这个能合并成一句吗?select count(ITEMKIND) from ITEM where ITEMKIND='1' ; select count(ITEMKIND) from ITEM where ITEMKIND='2 ;select count(ITEMKIND) from ITEM where ITEMKIND='3' ;select count(ITEMKIND) from ITEM where ITEMKIND='4' ; select co mysql_query(select Count(1) from account 怎么判断设置 输出数值?我要输出下面这一段 让収条件 不成立$check_query = mysql_query(select Count(1) from account where username='$username' and sha_pass_hash ='$password';); if 这 SELECT sum(1) FROM table;和SELECT count(1) FROM table;SELECT sum(1) FROM table;----------------累加'1'列的总和;SELECT count(1) FROM table;--------------统计'1'列的总条数;这里总和与总条数有何不同?应该是这样：如果：SE select count(*)和select (1)select count(*)返回所有满足条件的记录数,此时同select sum(1) 但是sum()可以传任意数字,负数、浮点数都可以,返回的值是传入值n*满足条件记录数m1、可以解释下这段话的含 SQL语句理解 select * from B where (select count(1) as num from A where A.ID = B.ID) = 0select * from B where (select count(1) as num from A where A.ID = B.ID) = 0请问如何理解,为什么 可以在B表中 排除A表的数据 select telnum,count(0),count(distinct othertelnum) from nmk.ljdx_cdr_temp group by telnum 下面这段代码什么意思,主要是后面条件delete from ware where ware_wareid in （select ware_wareid from ware where ware_deleted is null group by ware_wareid having count（ware_wareid） > 1） and rowid not in （select min（ select a.* from test a where 1 > (select count(*) from test where name = a.name and val > a.val )sql语句,按name分组显示最大的val值的字段,不明白具体意思, com.accp.dao.impl.StudentsDAOImpl@1ba92dbHibernate:select top 2 students0_.id as id0_,students0_.class_id as class2_0_,students0_.name as name0_,students0_.age as age0_ from students students0_ order by students0_.id descHibernate:select count(*) as SQL里的DISTINCT什么意思SELECT Sno,AVG(Grade)FROM SCGROUP BY SnoHAVING COUNT(DISTINCT(Sno))>1;既然已经按Sno分类了,再用DISTINCT那HAVING COUNT(DISTINCT(Sno))的值岂不是只能为1?