Shulou(Shulou.com)06/01 Report--

This article describes the basic query oracle examples usage. Share it for your reference, as follows:

Basic select statements

SELECT *|{[DISTINCT] column|expression [alias], ...} FROM table;

For example:

--Query all data select * from emp;--Query specified column data select empno,ename,sal from emp;--Arithmetic operator (+ - * /)select ename,sal,sal+30 from emp;--Use parentheses select ename,sal,12*(sal+30) from emp;--Define null value--(null is invalid, unspecified, unknown or unpredictable, null is not a space or 0)select ename,job,sal,comm from emp;--null mathematical operations--null mathematical expressions all have null values select ename,12*sal+comm from emp;--column aliases--aliases use double quotes, AS can omit select deptno as "no", NAME as "name" from emp;--connectors, connecting columns with columns, columns with characters select deptno|| '--' ||NAME from emp;--String--Date and character can only appear in single quotes select 'hello '|| ename from emp;--delete duplicate rows select distinct deptno from emp;--show table structure desc[ribe] tablename;

II. Filtering and sorting

SELECT *|{[DISTINCT] column|expression [alias], ...} FROM table[WHERE condition(s)];

For example:

--Query specified conditional data select deptno,ename from emp where deptno=10;--String and date enclosed in single quotes--String case sensitive, date format sensitive select ename,job,deptno from emp where ename='King';--Comparison operator (= >

< = !=)select ename,sal from emp where sal1500; 排序 ORDER BY 字段 [DESC|ASC] 例如： select ename,sal from emp order by sal desc;--多列排序--先按第一列排序，如果相同，则按第二列排序，以此类推select * from emp order by sal desc,hiredate desc; 三、单行函数 1、字符函数 --LOWER 转换小写--UPPER 转换大写--INITCAP 首字母大写select lower(ename) from emp;--CONCAT 接接字符串--SUBSTR 截取字符串--LENGTH 字符串长度--INSTR 查找字符串--LPAD 左边填充字符--RPAD 右边填充字符--TRIM([leading|trailing|both] 字符串1 from 字符串2) --TRIM可以删除两边空格，也可删除其他字符--REPLACE 替换字符串select concat('aa','bb') from emp;select substr('abcdefg', 2, 3) from emp;select length('test...') from emp;select instr('hello world', 'w') from emp;select lpad(sal, '10', '0') from emp;select rpad(sal, '10', '*') from emp;select trim(' test ') from emp;--从尾部删除字符串*号select trim(trailing '*' from '**1212121**') from emp;--把字符串中的22替换成88select replace('11223344', '22', '88') from emp; 2、数字函数 --ROUND 四舍五入--TRUNC 截断--MOD 求余select round(25.533,2) from dual;select trunc(25.323,2) from dual;select mod(8, 3) from dual; 3、日期 oracle中日期型数据实际含有两个值：日期和时间。 默认格式为：DD-MON-RR --返回系统时间select sysdate from dual;--两个日期相减，返回日期之间相差的天数select ename,(sysdate-hiredate) / 7 "weeks" from emp;--MONTHS_BETWEEN 两日期相差月数--ADD_MONTHS 指定日期加上若干月数--NEXT_DAY 指定日期的下一个日期--LAST_DAY 本月的最后一天--ROUND 日期四舍五入--TRUNC 日期截断select months_between(sysdate,hiredate) from emp; 4、显式数据类型转换 --TO_CHAR(date, 'format_model')--把日期转换成字符串select to_char(sysdate, 'YYYY MM DD HH:MI:SS') from dual;--TO_CHAR(number, 'format_model')select ename,sal,to_char(sal, '$99,999.00') from emp;--TO_NUMBER(char[,'format_model'])--TO_DATE(char[,'format_model']) 通用函数，适用于任何数据类型，也适用于空值 NVL(expr1,expr2)NVL2(expr1,expr2,expr3)NULLIF(expr1,expr2)COALESCE(expr1,expr2,...) 5、条件表达式 在sql语句中使用if-then-else逻辑 case表达式，sql99语法，类似basic，比较繁锁 decode函数，oracle自已语法，类似java，比较简洁 CASE expr WHEN comparison_expr1 THEN return_expr1 [WHEN comparison_expr2 THEN return_expr2 WHEN comparison_expr3 THEN return_expr3 ELSE else_expr]ENDDECODE(col|expression, search2, result1 [,search3, result2, ..., ] [,defautl])select ename,sal,decode(round(sal/1000),1, '一倍'，2, '二倍'，3, '三倍','不知倍数') from emp; 6、函数嵌套 单行函数可以嵌套，嵌套函数的执行是由内到外。 四、分组函数 分组函数作用于一组数据，并对一组数据返回一个值。 常用组函数 --AVG--COUNT--MAX--MIN--SUMselect sum(sal) as "total" from emp;select max(sal) from emp;select count(*) from emp where deptno=10;select count(distinct deptno) from emp; 分组数据 通过GROUP BY可以将数据分成若干组 select deptno,avg(sal) from emp group by deptno; (*注意：在select列表中所有未包含在组函数中的列都必须包含在group by中。) --多列分组select deptno,job,avg(sal) from emp group by deptno,job; 过滤分组 通过HAVING子句对分组进行过滤 select deptno,avg(sal) from emp group by deptno having deptno in(10,20); (*注意：不能在where子句中使用组函数，having子句中可以。) 嵌套组函数 select max(avg(sal)) from emp group by deptno; 五、多表查询 oracle的连接 sql99的连接 等值连接 cross joins 不等值连接 natural joins 外连接 using clause 自连接 full or two sided outer joins SELECT table1.column, table2.columnFROM table1,table2WHERE table1.column1=table2.column2;--等值连接select d.dname,e.ename,e.sal from emp e, dept d where e.deptno=d.deptno;--多连接条件和and操作符select d.dname,e.ename,e.sal from emp e, dept d where e.deptno=d.deptno and e.deptno=10; 表的别名 1、使用表别名可简化查询 2、使用表名前缀可以提高执行效率 3、如果使用了表的别名，则不能再使用表的真名。 --不等值连接--查询员工部门名称和工资等级select d.dname, e.ename, e.sal, s.gradefrom emp e, dept d, salgrade swhere e.deptno = d.deptnoand e.sal >

= s.losaland e.sal

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