oracle9i学习笔记

sect select col1,col2,col3 from table2_name;

/*minus 操作，集合减,它将压缩两个集合减后的重复记录, 且对数据排序*/
select col1,col2,col3 from table1_name minus select col1,col2,col3 from table2_name;

/*EXTRACT 抽取时间函数. 此例是抽取当前日期中的年*/
select EXTRACT(YEAR FROM SYSDATE) from dual;
/*EXTRACT 抽取时间函数. 此例是抽取当前日期中的月*/
select EXTRACT(MONTH FROM SYSDATE) from dual;

########################## 增强的 group by 子句 #########################

select [column,] group_function(column)...
from table
[WHERE condition]
[GROUP BY [ROLLUP] group_by_expression]
[HAVING having_expression];
[ORDER BY column]; -------ROLLUP操作字，对group by子句的各字段从右到左进行再聚合

example:
/*其结果看起来象对col1做小计*/
select col1,col2,sum(col3) from table group by rollup(col1,col2);
/*复合rollup表达式*/
select col1,col2,sum(col3) from table group by rollup((col1,col2));

select [column,] group_function(column)...
from table
[WHERE condition]
[GROUP BY [CUBE] group_by_expression]
[HAVING having_expression];
[ORDER BY column]; -------CUBE操作字，除完成ROLLUP的功能外，再对ROLLUP后的结果集从右到左再聚合

example:
/*其结果看起来象对col1做小计后，再对col2做小计，最后算总计*/
select col1,col2,sum(col3) from table group by cube(col1,col2);
/*复合rollup表达式*/
select col1,col2,sum(col3) from table group by cube((col1,col2));
/*混合rollup,cube表达式*/
select col1,col2,col3,sum(col4) from table group by col1,rollup(col2),cube(col3);

/*GROUPING(expr)函数，查看select语句种以何字段聚合，其取值为0或1*/
select [column,] group_function(column)...,GROUPING(expr)
from table
[WHERE condition]
[GROUP BY [ROLLUP] group_by_expression]
[HAVING having_expression];
[ORDER BY column];

example:
select col1,col2,sum(col3),grouping(col1),grouping(col2) from table group by cube(col1,col2);

/*grouping sets操作，对group by结果集先对col1求和，再对col2求和，最后将其结果集并在一起*/
select col1,col2,sum(col3) from table group by grouping sets((col1),(col2));

 

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