SQL语句学习积累笔记

1.Oracle数据库查询某一时间段内的数据
eg.查询T_TABLE_NAME中过去一周的数据总和，时间字段为date

SELECT count(ID)
FROM T_TABLE_NAME
WHERE date
BETWEEN TRUNC(sysdate -7) and TRUNC(sysdate)

2.Oracle数据库查询/删除同一张表中的重复记录
（1）查找表中多余的重复记录，重复记录是根据单个字段来判断
eg.查询T_TABLE_NAME中字段id重复的记录

SELECT *
FROM 
	T_TABLE_NAME
GROUP BY
	id 
HAVING
	count( id ) > 1

（2）查找表中多余的重复记录，重复记录是根据多个字段来判断
eg.查询T_TABLE_NAME中字段id和字段name同时重复的记录，并根据id进行降序排序

SELECT * 
FROM
	T_TABLE_NAME 
WHERE
	( T_TABLE_NAME.id, T_TABLE_NAME.name ) IN ( SELECT id, name T_TABLE_NAME GROUP BY id, name HAVING count( * ) > 1 )
ORDER BY id DESC

（3）查找表中多余的重复记录，重复记录是根据多个字段来判断，只留有rowid最小的记录
eg.查询T_TABLE_NAME中字段id和字段name同时重复的记录，只留number最小的记录

SELECT * 
FROM
	T_TABLE_NAME
WHERE
	( T_TABLE_NAME.id, T_TABLE_NAME.name ) IN ( SELECT id, name FROM T_TABLE_NAME GROUP BY id, name HAVING count( * ) > 1 ) 
	AND number NOT IN ( SELECT min( number ) FROM T_TABLE_NAME GROUP BY id, name HAVING count( * ) > 1 )

（4）删除表中多余的重复记录，重复记录是根据多个字段来判断，只留有rowid最小的记录
eg.删除T_TABLE_NAME中字段id和字段name同时重复的记录，只留number最小的记录

DELETE 
FROM
	T_TABLE_NAME 
WHERE
	(  T_TABLE_NAME.id, T_TABLE_NAME.name  ) IN ( SELECT id, name FROM T_TABLE_NAME GROUP BY id, name HAVING count( * ) > 1 ) 
	AND number NOT IN ( SELECT min( number ) FROM T_TABLE_NAME GROUP BY id, name HAVING count( * ) > 1 )

3.Oracle数据库中查询不重复数据
eg.查询T_TABLE_NAME中字段id和字段name同时均不重复的记录

SELECT DISTINCT id,name
FROM T_TABLE_NAME