SELECT COUNT(*) AS COUNT,REQUEST,METHOD FROM REQUESTMETH GROUP BY
REQUEST,METHOD HAVING (REQUEST ='FC.OCEAN.JOB.SERVER.CBIZOZBKHEADER' OR REQUEST='FC.Ocean.Job.Server.CBizOzDocHeader')
AND COUNT(*) >3
ORDER BY REQUEST
如上语句的注意事项
HAVING后的条件不能用别名COUNT>3 必须使用COUNT(*) >3，否则报：列名 'COUNT' 无效。
having 子句中的每一个元素并不一定要出现在select列表中，如上面的语句可以写成：
SELECT REQUEST,METHOD FROM REQUESTMETH GROUP BY
REQUEST,METHOD HAVING (REQUEST ='FC.OCEAN.JOB.SERVER.CBIZOZBKHEADER' OR REQUEST='FC.Ocean.Job.Server.CBizOzDocHeader')
AND COUNT(*) >3
ORDER BY REQUEST
SELECT COUNT(*) AS COUNT,REQUEST,METHOD FROM REQUESTMETH GROUP BY
REQUEST,METHOD ORDER BY REQUEST
如果把该语句写成：
SELECT COUNT(*) AS COUNT,REQUEST,METHOD FROM REQUESTMETH GROUP BY
REQUEST ORDER BY REQUEST
那么将报：
选择列表中的列 'REQUESTMETH.method' 无效，因为该列没有包含在聚合函数或 GROUP BY 子句中。
注意：
1、使用GROUP BY 子句时，SELECT 列表中的非汇总列必须为GROUP BY 列表中的项。
2、分组时，所有的NULL值分为一组。
3、GROUP BY 列表中一般不允许出现复杂的表达试、显示标题以及SELECT列表中的位置标号。
如：SELECT REQUEST,METHOD, COUNT(*) AS COUNT FROM REQUESTMETH GROUP BY
REQUEST,2 ORDER BY REQUEST 是错误的。
错误信息为：每个 GROUP BY 表达式都必须包含至少一个列引用。
SELECT COUNT(*) AS COUNT, MAX(BOOKID) AS MAXBOOKID,CATEGORYID FROM BOOK
WHERE DOTNUMBER >10 GROUP BY CATEGORYID
HAVING MAX(BOOKID) < 50
ORDER BY CATEGORYID
以上语句：先过滤出点击率大于10的，然后按类型(CATEGORYID )进行分组，再过滤出每组的最大值小于50个
行，最后进行按CATEGORYID进行排序。
GROUP BY 中使用 ORDER BY注意事项：
SELECT COUNT(*) AS COUNT FROM REQUESTMETH GROUP BY REQUEST,METHOD ORDER BY REQUEST,METHOD
--这样是允许的, ORDER BY后面的字段包含在GROUP BY 子句中
SELECT COUNT(*) AS COUNTS FROM REQUESTMETH GROUP BY REQUEST ORDER BY COUNT(*) DESC
--这样是允许的，ORDER BY后面的字段包含在聚合函数中，结果集同下面语句一样
SELECT COUNT(*) AS COUNTS FROM REQUESTMETH GROUP BY REQUEST ORDER BY COUNTS DESC
--这样是允许的，区别于HAVING，HAVING后不允许跟聚集函数的别名作为过滤条件
SELECT COUNT(*) AS COUNTS FROM REQUESTMETH GROUP BY REQUEST ORDER BY METHOD
--这样是错误的：ORDER BY 子句中的列 "REQUESTMETH.method" 无效，因为该列没有包含在聚合函数或 GROUP BY 子句中。
SELECT DISTINCT 中使用 ORDER BY注意事项：
SELECT DISTINCT BOOKID FROM BOOK ORDER BY BOOKNAME
以上语句将报：
--如果指定了SELECT DISTINCT，那么ORDER BY 子句中的项就必须出现在选择列表中。
因为以上语句类似
SELECT BOOKID FROM BOOK GROUP BY BOOKID ORDER BY BOOKNAME
其实错误信息也为：
--ORDER BY子句中的列"BOOK.BookName" 无效，因为该列没有包含在聚合函数或GROUP BY 子句中。
应该改为：SELECT DISTINCT BOOKID,BOOKNAME FROM BOOK ORDER BY BOOKNAME
SELECT DISTINCT BOOKID,BOOKNAME FROM BOOK
SELECT BOOKID,BOOKNAME FROM BOOK GROUP BY BOOKID,BOOKNAME
以上两句查询结果是一致的，DISTINCT的语句其实完全可以等效的转换为GROUP BY语句