1.使用sys对scott用户进行解锁和重置密码：
alter user scott identified by tiger account unlock;
2.书写sql语句
1）sql语句不区分大小写
2）sql语句可以分成一行或者多行写
3）关键字不可以简写或者多行分写
4）子句通常分行写
5）使用缩进提高可读性
6）关键字通常用大写，其他的词像表名或者列名用小写
3.可以将显示的结果直接进行算术运行，产生的结果不改变数据库中的值，称为伪列
SQL> select ename,sal*1.1 from emp; //将工资乘以1.1倍显示 ENAME SAL*1.1 -------------------- ---------- SMITH 880 ALLEN 1760 WARD 1375 JONES 3272.5 MARTIN 1375 BLAKE 3135 CLARK 2695 SCOTT 3300 KING 5500 TURNER 1650 ADAMS 1210 ENAME SAL*1.1 -------------------- ---------- JAMES 1045 FORD 3300 MILLER 1430 14 rows selected.
4.连接操作符
1）将多列连接在一起显示
USER is "SCOTT" SQL> select ename||job from emp; //将ename列和job列连接在一起显示 ENAME||JOB -------------------------------------- SMITHCLERK ALLENSALESMAN WARDSALESMAN JONESMANAGER MARTINSALESMAN BLAKEMANAGER CLARKMANAGER SCOTTANALYST KINGPRESIDENT TURNERSALESMAN ADAMSCLERK ENAME||JOB -------------------------------------- JAMESCLERK FORDANALYST MILLERCLERK 14 rows selected
2）将多列连接在一起显示，中间可以插入其它字符
SQL> select ename|| ' is a ' || job from emp; //两列中间插入 is a ENAME||'ISA'||JOB -------------------------------------------------- SMITH is a CLERK ALLEN is a SALESMAN WARD is a SALESMAN JONES is a MANAGER MARTIN is a SALESMAN BLAKE is a MANAGER CLARK is a MANAGER SCOTT is a ANALYST KING is a PRESIDENT TURNER is a SALESMAN ADAMS is a CLERK ENAME||'ISA'||JOB -------------------------------------------------- JAMES is a CLERK FORD is a ANALYST MILLER is a CLERK 14 rows selected.
3）善用连接符。如生成删除表的命令，可以放到脚本中运行。
SQL> select 'drop table ' ||tname||';'from tab; //删除表 'DROPTABLE'||TNAME||';' -------------------------------------------------------------------------------- drop table BONUS; drop table DEPT; drop table EMP; drop table SALGRADE;
4.压缩重复的行。只有查询的列中每一行都重复的情况下，才会压缩显示。
SQL> select distinct deptno from emp; DEPTNO ---------- 30 20 10 SQL> select distinct deptno,job from emp; DEPTNO JOB ---------- ------------------ 20 CLERK 30 SALESMAN 20 MANAGER 30 CLERK 10 PRESIDENT 30 MANAGER 10 CLERK 10 MANAGER 20 ANALYST 9 rows selected.
5.限制返回的行信息
1）where 条件： 对条件进行判断，如果值为true 则执行，否则不执行。这里的条件可以是逻辑语句。与 and、或 or、非 not，这几个逻辑词可一起使用。
SQL> select job from emp where not sal<1000; //工资大于等于1000的工作。 JOB ------------------ SALESMAN SALESMAN MANAGER SALESMAN MANAGER MANAGER ANALYST PRESIDENT SALESMAN CLERK ANALYST CLERK 12 rows selected.
2）where 条件：条件是字符串的时候，大小写敏感。条件是日期的时候，格式敏感，且这两者都要放到单引号中。
SQL> select * from emp where hiredate='17-nov-81'; //查询日期的时候，大小写不区分，但是格式敏感。 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7839 KING PRESIDENT 17-NOV-81 5000 10
3）where 条件：between 1000 and 3000，闭区间，大于等于1000小于等于3000。
SQL> select job from emp where sal between 1000 and 3000; //选出工资在1000到3000之间的工作 JOB ------------------ SALESMAN SALESMAN MANAGER SALESMAN MANAGER MANAGER ANALYST SALESMAN CLERK ANALYST CLERK 11 rows selected.
4）where 条件：in {' ',' '}，是一个枚举型，括号里面跟随的是集合列表，可以跟随多个元素，但是类型必须一致。
SQL> select * from emp where job in ('CLERK','SALESMAN'); //查看clerk和salesman职员的详细信息 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7369 SMITH CLERK 7902 17-DEC-80 800 20 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7934 MILLER CLERK 7782 23-JAN-82 1300 10 8 rows selected.
5）where 条件：is null，对值是否为空值进行判断
SQL> select * from emp where comm is null; //查看奖金为空值的信息 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7369 SMITH CLERK 7902 17-DEC-80 800 20 7566 JONES MANAGER 7839 02-APR-81 2975 20 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7788 SCOTT ANALYST 7566 19-APR-87 3000 20 7839 KING PRESIDENT 17-NOV-81 5000 10 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7934 MILLER CLERK 7782 23-JAN-82 1300 10 10 rows selected. SQL> select * from emp where comm is not null; //查看奖金为非空值的信息 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
6）where 条件：like 模糊匹配
SQL> select * from emp where ename like 'A%'; //%匹配所有的意思 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 SQL> select * from emp where ename like '_O%'; //'_'单个通配符 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7566 JONES MANAGER 7839 02-APR-81 2975 20 7902 FORD ANALYST 7566 03-DEC-81 3000 20 SQL> select * from emp where ename like '_/_%'escape'/'; //escape，可以将任意字符定义转义字符，这里是将/定义为转义字符。 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7788 X_SCOTT ANALYST 7566 19-APR-87 3000 20
7）结果集中有一个oracle隐藏的伪列 ，称为结果集的编号列rownum列。
scott@TEST>select ename,sal from(select * from emp order by sal desc) where rownum < 4; //对工资进行排序 ENAME SAL -------------------- ---------- KING 5000 SCOTT 3000 FORD 3000 scott@TEST>select ename,sal from (select rownum bb,ename,sal from (select rownum ,ename,sal from emp order by sal desc))where bb=2; //找出第二名工资 ENAME SAL -------------------- ---------- FORD 3000
6.order by 子句来进行排序操作
默认是升序 asc
降序时指定 desc
这里也可以进行多列排序，按照先后顺序进行排序。
SQL> select * from emp order by sal; //对工资进行升序排序 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7369 SMITH CLERK 7902 17-DEC-80 800 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7934 MILLER CLERK 7782 23-JAN-82 1300 10 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7566 JONES MANAGER 7839 02-APR-81 2975 20 7788 X_SCOTT ANALYST 7566 19-APR-87 3000 20 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7839 KING PRESIDENT 17-NOV-81 5000 10 14 rows selected. SQL> select * from emp order by sal desc; //对工资进行降序排序 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- -------------------- ------------------ ---------- ------------ ---------- ---------- ---------- 7839 KING PRESIDENT 17-NOV-81 5000 10 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7788 X_SCOTT ANALYST 7566 19-APR-87 3000 20 7566 JONES MANAGER 7839 02-APR-81 2975 20 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7934 MILLER CLERK 7782 23-JAN-82 1300 10 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7369 SMITH CLERK 7902 17-DEC-80 800 20 14 rows selected. SQL> select sal,comm*2 from emp order by comm*2,sal; //先按照奖金的顺序排序，然后在按照工资的顺序进行排序 SAL COMM*2 ---------- ---------- 1500 0 1600 600 1250 1000 1250 2800 800 950 1100 1300 2450 2850 2975 3000 3000 5000 14 rows selected.