普通查询
- 实际开发慎用
SELECT * FROM EMP;
查询指定列
SELECT EMPNO,ENAME,JOB,SAL FROM EMP;
查询指定行
SELECT EMPNO,ENAME,JOB,SAL,DEPTNO FROM EMP WHERE DEPTNO=10;
查询部门号为20的员工信息，且工资大于1500
SELECT * FROM EMP WHERE DEPTNO=20 AND SAL>1500;
别名的使用
SELECT EMPNO 员工号,ENAME 姓名,JOB 职位,SAL 薪资 FROM EMP;
SELECT EMPNO AS 员工号,ENAME AS 姓名 FROM EMP;
SELECT E.ENAME,E.JOB FROM EMP E;
查询中使用NULL
- 0不是NULL
SELECT * FROM EMP WHERE COMM IS NULL;
使用常量
SELECT EMPNO,ENAME,'潭州' 工作单位 FROM EMP;
伪列
- 建立时按顺序，使用条件将始终为1
- 等于和大于超过1将失效
SELECT ROWNUM,E.* FROM EMP E;
SELECT ROWNUM,EMPNO,ENAME FROM EMP WHERE ROWNUM<5;
SELECT ROWNUM,EMPNO,ENAME FROM EMP WHERE ROWNUM>5;
SELECT ROWNUM,EMPNO,ENAME FROM EMP WHERE ROWNUM=5;
SELECT ROWNUM,E.* FROM EMP E ORDER BY SAL;
排序
- ORDER BY
- ASC(默认)升序，DESC 降序
SELECT * FROM EMP ORDER BY SAL ASC;
SELECT * FROM EMP ORDER BY SAL DESC;
SELECT * FROM EMP ORDER BY HIREDATE; --(时间类型排序)
SELECT * FROM EMP ORDER BY HIREDATE DESC;
SELECT * FROM EMP ORDER BY ENAME; --(字符串排序)
查询员工信息，按照工资额升序，如果工资一致就安照入职时间降序
SELECT * FROM EMP ORDER BY SAL,HIREDATE ASC;
分页查询
SELECT S.* FROM
(SELECT ROWNUM R,E.* FROM
(SELECT * FROM EMP ORDER BY SAL) E) S
WHERE R>5 AND R<=10;
查询工资大于2000的员工进行排序
SELECT * FROM EMP WHERE SAL>2000 ORDER BY SAL;
使用别名进行年薪排序
SELECT EMPNO,ENAME,JOB,SAL*12 年薪 FROM EMP ORDER BY 年薪;
范围查询
- BETWEEN..AND 范围查找
- IN 包含查找
- LIKE 正则表达式模糊查找
BETWEEN
SELECT * FROM EMP WHERE SAL BETWEEN 2000 AND 3000;
SELECT * FROM EMP WHERE SAL>=2000 AND SAL<=3000;
IN
SELECT * FROM EMP WHERE DEPTNO IN(10,20);
SELECT * FROM EMP WHERE DEPTNO=20 OR DEPTNO=10;
LIKE
SELECT * FROM EMP WHERE ENAME LIKE '%A%';
SELECT * FROM EMP WHERE ENAME LIKE 'A%';
SELECT * FROM EMP WHERE ENAME LIKE '_A%';
拓展
查询当前登录用户
SELECT USER FROM DUAL; --DUAL 虚表
查询表的约束
SELECT * FROM USER_CONSTRAINTS WHERE TABLE_NAME='EMP';
查询表结构
SELECT * FROM USER_TAB_COLS WHERE TABLE_NAME='EMP';
查看当前用户下所有表
SELECT TABLE_NAME FROM USER_TABLES;