Oracle 中的sql函數以及分頁
SELECT LPAD(‘Page 1‘,15,‘*.‘) "LPAD example" FROM DUAL;
1.分頁查詢
(1)方法一:使用 between and 來實現分頁
select * from ( select emp.*,rownum rn from emp ) where rn between 4 and 6
(2)方法二:使用 rownum 來實現分頁
select * from ( select emp.*,rownum rn from emp where rownum<=6 ) where rn>=4
(3)方法三:使用rownum 三層來實現分頁
select * from ( select emp.*,rownum rn from ( select * from emp )emp where rownum<=6 ) where rn >=4
得到的結果如下:
2.分析函數
(1)rank() :rank()函數返回一個唯一的值,當遇到相同的數據時,所有相同數據的排名是一樣的,
同時會在最後一條相同記錄和下一條不同記錄之間空出排名。
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
結果:
(2)dense_rank() :dense_rank()函數返回一個唯一的值,當遇到相同數據時,所有相同的數據的排名都是一樣的。
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()函數返回一個唯一的值,當遇到相同數據時,排名按照記錄集中記錄的順序依次遞增。
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)合並結果:
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函數
(1)字符函數
1.大小寫控制函數
lower():全部小寫
SELECT LOWER(‘MR. SCOTT MCMILLAN‘) "Lowercase" FROM DUAL;
upper():全部大寫
SELECT UPPER(‘abc‘) "Uppercase" FROM dual;
initcap():首字母大寫
SELECT initcap(‘MR. SCOTT MCMILLAN‘) "initcap" FROM DUAL;
2.字符控制函數
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) 說明:位置從1開始
select substr(‘HappyBoy‘,4) from dual;
substr(‘要截取的字符,起始位置,取幾個字符)
select substr(‘HappyBoy‘,2,3) from dual;
length(‘字符串‘):字符個數統計
lengthb(‘字符串‘):字節個數統計
select length(‘快樂‘) 字符數,lengthb(‘快樂‘) as 字節數 from dual;
instr(‘大字符串‘,‘小字符串‘)返回小字符串在大字符串中出現的位置
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)日期函數
1.日期函數
months_between()兩個日期相差的月數
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幹月數
SELECT TO_CHAR(ADD_MONTHS(hiredate, 1), ‘DD-MON-YYYY‘) "Next month" FROM emp WHERE ename = ‘JONES‘;
2.日期相減
兩個日期相差的天數
select floor(sysdate-to_date(‘2015-12-12‘,‘yyyy-MM-dd‘)) from dual;
兩個日期相差的月數
select months_between(sysdate,to_date(‘20151212‘,‘yyyyMMdd‘)) from dual;
(3)轉換函數
1.隱式轉換
select * from emp where hiredate=‘17-12月-80‘;
2.顯式轉換
to_char()對日期的轉換
select to_char(sysdate,‘yyyy-MM-dd hh24:mi:ss‘) from dual;
to_char()對數字的轉換
select to_char(sal,‘L9999.99‘) from emp;
(4)數字函數
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)通用函數
1.nvl()濾空函數
SELECT SAL*12 工資,comm 獎金,sal*12+nvl(comm,0) from emp;
2.nvl2()濾空函數
SELECT SAL*12 工資,comm 獎金,sal*12+nvl2(comm,comm,0) from emp;
3.不用濾空函數
SELECT SAL*12 工資,comm 獎金,sal*12 from emp;
(6)decode函數
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";
Oracle 中的sql函數以及分頁