Oracle 中的sql函数以及分页
Posted 刘二雄
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SELECT LPAD(\'Page 1\',15,\'*.\') "LPAD example" FROM DUAL;
1.分页查询
(1)方法一:使用 between and 来实现分页
select * from ( select emp.*,rownum rn from emp ) where rn between 4 and 6
(2)方法二:使用 rownum 来实现分页
select * from ( select emp.*,rownum rn from emp where rownum<=6 ) where rn>=4
(3)方法三:使用rownum 三层来实现分页
select * from ( select emp.*,rownum rn from ( select * from emp )emp where rownum<=6 ) where rn >=4
得到的结果如下:
2.分析函数
(1)rank() :rank()函数返回一个唯一的值,当遇到相同的数据时,所有相同数据的排名是一样的,
同时会在最后一条相同记录和下一条不同记录之间空出排名。
select ename,deptno,sal, rank() over(partition by deptno order by sal desc) "RANK" --dense_rank() over(partition by deptno order by sal desc)"dense_rank" --row_number() over(partition by deptno order by sal desc)"row_number" from emp
结果:
(2)dense_rank() :dense_rank()函数返回一个唯一的值,当遇到相同数据时,所有相同的数据的排名都是一样的。
select ename,deptno,sal, --rank() over(partition by deptno order by sal desc) "RANK" dense_rank() over(partition by deptno order by sal desc)"dense_rank" --row_number() over(partition by deptno order by sal desc)"row_number" from emp
(3)row_number():row_number()函数返回一个唯一的值,当遇到相同数据时,排名按照记录集中记录的顺序依次递增。
select ename,deptno,sal, --rank() over(partition by deptno order by sal desc) "RANK" --dense_rank() over(partition by deptno order by sal desc)"dense_rank" row_number() over(partition by deptno order by sal desc)"row_number" from emp
(4)合并结果:
select ename,deptno,sal, rank() over(partition by deptno order by sal desc) "RANK", dense_rank() over(partition by deptno order by sal desc)"dense_rank", row_number() over(partition by deptno order by sal desc)"row_number" from emp
3.SQL函数
(1)字符函数
1.大小写控制函数
lower():全部小写
SELECT LOWER(\'MR. SCOTT MCMILLAN\') "Lowercase" FROM DUAL;
upper():全部大写
SELECT UPPER(\'abc\') "Uppercase" FROM dual;
initcap():首字母大写
SELECT initcap(\'MR. SCOTT MCMILLAN\') "initcap" FROM DUAL;
2.字符控制函数
concat:拼接字符串
select concat(\'Happy\',\'Boy\') from dual;
substr:截取字符串
substr(\'要截取的字符串\',起始位置) 说明:位置从1开始
select substr(\'HappyBoy\',4) from dual;
substr(\'要截取的字符,起始位置,取几个字符)
select substr(\'HappyBoy\',2,3) from dual;
length(\'字符串\'):字符个数统计
lengthb(\'字符串\'):字节个数统计
select length(\'快乐\') 字符数,lengthb(\'快乐\') as 字节数 from dual;
instr(\'大字符串\',\'小字符串\')返回小字符串在大字符串中出现的位置
SELECT INSTR(\'CORPORATE FLOOR\',\'OR\', 3, 2) "Instring" FROM DUAL;
lpad()和rpad()
SELECT LPAD(\'Page 1\',15,\'*.\') "LPAD example" FROM DUAL;
SELECT ename, RPAD(\' \', sal/1000/1, \'*\') "Salary" FROM emp WHERE deptno=20 ORDER BY ename, "Salary";
trim()
select trim(\'a\' from \'ahappy\') from dual;
(2)日期函数
1.日期函数
months_between()两个日期相差的月数
SELECT MONTHS_BETWEEN (TO_DATE(\'02-02-1995\',\'MM-DD-YYYY\'),TO_DATE(\'01-01-1995\',\'MM-DD-YYYY\') ) "Months" FROM DUAL;
add_months():向指定日期中加上若干月数
SELECT TO_CHAR(ADD_MONTHS(hiredate, 1), \'DD-MON-YYYY\') "Next month" FROM emp WHERE ename = \'JONES\';
2.日期相减
两个日期相差的天数
select floor(sysdate-to_date(\'2015-12-12\',\'yyyy-MM-dd\')) from dual;
两个日期相差的月数
select months_between(sysdate,to_date(\'20151212\',\'yyyyMMdd\')) from dual;
(3)转换函数
1.隐式转换
select * from emp where hiredate=\'17-12月-80\';
2.显式转换
to_char()对日期的转换
select to_char(sysdate,\'yyyy-MM-dd hh24:mi:ss\') from dual;
to_char()对数字的转换
select to_char(sal,\'L9999.99\') from emp;
(4)数字函数
1.round():四舍五入
select round(12.45,1) from dual;
2.trunc
SELECT TRUNC(TO_DATE(\'2015-12-12\',\'yyyy-MM-dd\'), \'YEAR\') "New Year" FROM DUAL;
select trunc(15.71,1) "trunc" from dual;
(5)通用函数
1.nvl()滤空函数
SELECT SAL*12 工资,comm 奖金,sal*12+nvl(comm,0) from emp;
2.nvl2()滤空函数
SELECT SAL*12 工资,comm 奖金,sal*12+nvl2(comm,comm,0) from emp;
3.不用滤空函数
SELECT SAL*12 工资,comm 奖金,sal*12 from emp;
(6)decode函数
SELECT product_id, DECODE (warehouse_id,
1, \'Southlake\', 2, \'San Francisco\', 3, \'New Jersey\', 4, \'Seattle\', \'Non domestic\') "Location" FROM inventories WHERE product_id < 1775 ORDER BY product_id, "Location";
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