first_name請用兩種方式：
1.查詢員工表中所有員工名字及員工工資並按從小到大的順序排列
select first_name,salary from s_emp order by salary;
select first_name ,salary from s_emp order by 2;
select first_name ,salary from s_emp order by 1;
2.查詢員工表中所有員工名字及員工工資並按從大到小的順序排列
select first_name,salary from s_emp order by 2 desc;
3.查詢員工表中所有員工名字及員工工資並按名字從大到小的順序排列
select first_name,salary from s_emp order by 1;
select first_name,salary from s_emp order by first_name desc;
4.查詢員工表中所有員工名字及員工工資並按工資從小到大，名字從大到小的順序排列
select first_name ,salary from s_emp order by salary,first_name desc;
select first_name ,salary from s_emp order by 2,1 desc;
5.查詢員工表中編號為14的員工(標題為stock clerk)
select * from s_emp;
select *from s_emp where id=14;
select *from s_emp where id>14;
select *from s_emp where id<14;
select *from s_emp where id>=14;
select *from s_emp where id<=14;
select *from s_emp where id<>14;
select *from s_emp where id!=14;
select *from s_emp where id^=14;
select * from s_emp where title = 'stock clerk';
6.查詢員工表中編號在12到24之間的記錄
select * from s_emp where id between 12 and 24;
7.查詢員表中編號為1,3,8的記錄
select * from s_emp where id in(1,3,8);
8.查詢員工表中姓名包含a字母的員工資訊
select * from s_emp where first_name like '%a%';
select * from s_emp where first_name like '_a_';
9.查詢員工表中提成為空的所有員工資訊
select * from s_emp where commission_pct is null;
10.查詢員工表中編號不在12到24之間的記錄
select *from s_emp where id not between 12 and 24;
11.查詢員表中編號不為1,3,8的記錄
select * from s_emp where id not in (1,3,8);
12.查詢員工表中姓名不包含a字母的員工資訊
select *from s_emp where first_name not like '%a%';
13.查詢員工表中提成不為空的所有員工資訊
select * from s_emp where commission_pct is not null;
14.查詢員工表中id為11並且工資為1400的記錄
select * from s_emp where id=11 and salary=1400;
15.查詢員工表中id為11或者工資為1400的記錄
select * from s_emp where id=11 or salary=1400;
16.邏輯運算子多個混合使用
select* from s_emp wheresalary >= 1000 anddept_id = 44 ordept_id = 42 ;
select* from s_emp wheresalary >= 1000 and(dept_id = 44 ordept_id = 42 );
17.lower轉換為小寫
select lower('oracel') from dual;
18.upper轉換為大寫
select upper('oracel') from dual;
19.initcap轉換為首字母大寫
select initcap(' oh my ladygaga ') from dual;
20.concat字串連線 ||
select concat(first_name ,last_name) from s_emp;
select first_name ||'.'||last_name "姓名" from s_emp;
select concat(concat(first_name,'.'),last_name) from s_emp;
21.substr(原字串,起始值,返回子串的長度)返回子串
"my ladygaga" *****=>"lady"
select substr('my ladygaga',4,4) from dual ;
22.length(字串)返回長度
select first_name ,length(first_name) from s_emp;
23.round四捨五入
select round (45.923, 2) from dual;
select round (45.923, 0) from dual;
select round (45.923, -1) from dual;
24.trunc擷取
select trunc(45.923, 2) from dual;
select trunc(45.923, 0) from dual;
select trunc(45.923, -1) from dual;
25.檢視系統日期
select sysdate from dual;
26.查詢當前時間五天後的日期
select sysdate+5 from dual;
27.months_between 兩個日期中做計算(為毫秒數)
select months_between(sysdate,sysdate+30) from dual;
28.add_months當前時間增加（按月增加）
select add_months(sysdate,2) from dual;
29.next_day當前時間的下乙個時間
select next_day(sysdate,'星期一') from dual;
30.last_day本月的最後一天
select last_day(sysdate) from dual;
31.巢狀(sysdate,值)值可為 正 負
select last_day(add_months(sysdate,-1)) from dual;
32.to_char 轉換為字串
select to_char(1234) from dual;
select to_number(45678) from dual;
33.轉換為固定格式
select to_char(123456789,'fm$999,999,999') from dual;
34.to_date 轉換為日期
select to_date('04-3月 -90') from dual;
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