GR -- AC
SQL> select greatest('啊','安','天') from dual; GR -- 天
56.LEAST
返回一组表达式中的最小值
SQL> select least('啊','安','天') from dual; LE -- 啊
57.UID
返回标识当前用户的唯一整数 SQL> show user
USER 为\
SQL> select username,user_id from dba_users where user_id=uid;
USERNAME USER_ID ------------------------------ ---------
GAO 25
58.USER
返回当前用户的名字
SQL> select user from dual;
USER
------------------------------ GAO
59.USEREVN
返回当前用户环境的信息,opt可以是:
ENTRYID,SESSIONID,TERMINAL,ISDBA,LABLE,LANGUAGE,CLIENT_INFO,LANG,VSIZE ISDBA 查看当前用户是否是DBA如果是则返回true
SQL> select userenv('isdba') from dual;
USEREN ------ FALSE
SQL> select userenv('isdba') from dual;
USEREN ------ TRUE SESSION
返回会话标志
SQL> select userenv('sessionid') from dual;
USERENV('SESSIONID') --------------------
152 ENTRYID
返回会话人口标志
SQL> select userenv('entryid') from dual;
USERENV('ENTRYID') ------------------
0 INSTANCE
返回当前INSTANCE的标志
SQL> select userenv('instance') from dual;
USERENV('INSTANCE') -------------------
1 LANGUAGE
返回当前环境变量
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
---------------------------------------------------- SIMPLIFIED CHINESE_CHINA.ZHS16GBK LANG
返回当前环境的语言的缩写
SQL> select userenv('lang') from dual;
USERENV('LANG')
----------------------------------------------------
ZHS
TERMINAL
返回用户的终端或机器的标志
SQL> select userenv('terminal') from dual;
USERENV('TERMINA ---------------- GAO VSIZE(X)
返回X的大小(字节)数
SQL> select vsize(user),user from dual;
VSIZE(USER) USER
----------- ------------------------------ 6 SYSTEM
60.AVG(DISTINCT|ALL)
all表示对所有的值求平均值,distinct只对不同的值求平均值 SQLWKS> create table table3(xm varchar(8),sal number(7,2)); 语句已处理。
SQLWKS> insert into table3 values('gao',1111.11); SQLWKS> insert into table3 values('gao',1111.11); SQLWKS> insert into table3 values('zhu',5555.55); SQLWKS> commit;
SQL> select avg(distinct sal) from gao.table3;
AVG(DISTINCTSAL) ----------------
3333.33
SQL> select avg(all sal) from gao.table3;
AVG(ALLSAL) ----------- 2592.59
61.MAX(DISTINCT|ALL)
求最大值,ALL表示对所有的值求最大值,DISTINCT表示对不同的值求最大值,相同的只取一次 SQL> select max(distinct sal) from scott.emp;
MAX(DISTINCTSAL) ----------------
5000
62.MIN(DISTINCT|ALL)
求最小值,ALL表示对所有的值求最小值,DISTINCT表示对不同的值求最小值,相同的只取一次 SQL> select min(all sal) from gao.table3;
MIN(ALLSAL) ----------- 1111.11
63.STDDEV(distinct|all)
求标准差,ALL表示对所有的值求标准差,DISTINCT表示只对不同的值求标准差 SQL> select stddev(sal) from scott.emp;
STDDEV(SAL) ----------- 1182.5032
SQL> select stddev(distinct sal) from scott.emp;
STDDEV(DISTINCTSAL) -------------------
1229.951
64.VARIANCE(DISTINCT|ALL) 求协方差
SQL> select variance(sal) from scott.emp;
VARIANCE(SAL) -------------
1398313.9
65.GROUP BY
主要用来对一组数进行统计
SQL> select deptno,count(*),sum(sal) from scott.emp group by deptno;
DEPTNO COUNT(*) SUM(SAL) --------- --------- ---------
10 3 8750 20 5 10875 30 6 9400
66.HAVING
对分组统计再加限制条件
SQL> select deptno,count(*),sum(sal) from scott.emp group by deptno having count(*)>=5;
DEPTNO COUNT(*) SUM(SAL) --------- --------- ---------
20 5 10875 30 6 9400
SQL> select deptno,count(*),sum(sal) from scott.emp having count(*)>=5 group by deptno ;
DEPTNO COUNT(*) SUM(SAL) --------- --------- ---------
20 5 10875 30 6 9400
67.ORDER BY
用于对查询到的结果进行排序输出
SQL> select deptno,ename,sal from scott.emp order by deptno,sal desc;
DEPTNO ENAME SAL --------- ---------- ---------
10 KING 5000 10 CLARK 2450 10 MILLER 1300 20 SCOTT 3000 20 FORD 3000 20 JONES 2975 20 ADAMS 1100 20 SMITH 800 30 BLAKE 2850 30 ALLEN 1600 30 TURNER 1500 30 WARD 1250 30 MARTIN 1250 30 JAMES 950
