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。
[email protected]>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
[email protected]>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.
转载于:https://www.cnblogs.com/sangmu/p/6753196.html