SQL count()函数与sum()函数
count():
COUNT() 函数返回匹配指定条件的行数。SELECT COUNT(column_name) FROM table_name
COUNT(column_name) 函数返回指定列的值的数目(NULL 不计入)
1.SELECT COUNT(Customer) AS CustomerNilsen FROM Orders 返回CustomerNilsen表中customer字段有值的行数的统计数
2.SELECT COUNT(Customer) AS CustomerNilsen FROM Orders WHERE Customer='Carter' 返回CustomerNilsen表中customer字段有值的行数的统计数,并且值是'Carter'
3.SELECT age,name,COUNT(1) AS CustomerNilsen FROM Orders
WHERE name='张三' group by age,name 返回CustomerNilsen表中customer字段有值的行数的统计数,并且值是'张三',但是为什么要加,group by column_name
原因如下:
一步一个脚印,方便自己复习,欢迎大家指正,非常感谢,共同进步!
posted on 2012-06-01 10:08 lovebeauty 阅读(21196) 评论(0) 编辑 收藏 举报