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使用到的表，ORACLE数据库HR用户

查看整张表 查看指定的列（指出列名就行） SELECT department_id,department_name FROM departments; 使用算术表达式 SELECT employee_id,first_name,salary,salary+100,salary+(salary*0.1) from employees; 定义列别名（重命名列标题） SELECT last_name, last_name as xing, last_name shixing , last_name “hai shi XING” from employees; 连接运算符| |链接列或字符 first_name||last_name “xingming”：把姓名连接到一块，显示成一列。修改列名 first_name||’ ‘||last_name “shiyongkongge”：把姓名连接到一块，中间有空格。显示成一列 SELECT first_name,last_name, first_name||last_name “xingming” , first_name||’ '||last_name “shiyongkongge” from employees; 把两列连接成一列，中间加上自定义的内容 取消重复的值 有许多重复的值 不显示重复的值 SELECT distinct department_id from employees; SELECT distinct department_id,job_id from employees; 显示表的结构 desc 空值是未分配的或不适用的值, 空不等于零或空格 SELECT last_name,job_id,salary,commission_pct from employees; 包含空值进行计算结果为空

WHERE带条件的查询，用来限制选定的行

select * from employees where department_id=90; 字符串和数据值用单引号括起来 字符值区分大小写，日期值区分大小写 select employee_id,first_name,last_name,job_id from employees where first_name=‘Steven’; 没区分大小写，无法查询到 不加引号，报错 查询日期 select * from employees where hire_date = ‘24-12月-05’; 使用比较运算符 select first_name,last_name,salary from employees where salary>=15000; 查询在指定范围内的数值BETWEEN AND select first_name,last_name,salary from employees where salary BETWEEN 13000 AND 20000; 不能返着写，不然没结果 select first_name,last_name,salary from employees where salary BETWEEN 20000 AND 13000; varcher列中使用运算符 in运算符：查找指定的值 select first_name,last_name,salary from employees where salary in (10000,250000,17000); like运算符 select first_name,last_name,salary from employees where first_name like ‘S%’; 查询S开头的 select first_name,last_name,salary from employees where first_name like ‘%s’; 查询S结尾的 select first_name,last_name,salary from employees where first_name like ‘%am%’; select first_name,last_name,salary from employees where first_name like ‘_d%’; 前面匹配任意一个字符，第二个字第是d 前面匹配任意两个字符，第三个字第是d select first_name,last_name,salary from employees where first_name like ‘__s%’; 查询为null select first_name,last_name,commission_pct from employees where commission_pct is null; 查询非空 select first_name,last_name,commission_pct from employees where commission_pct is not null; employee_id不是100和101的 select first_name,last_name,employee_id,commission_pct from employees where employee_id not in (100,101); 只有它两不显示 显示不是以S开头的名 select first_name,last_name,salary from employees where first_name not like ‘S%’; 使用逻辑运算符定义条件 And同时满足两个条件 select email,last_name,salary,department_id from employees where salary >= 10000 and department_id=90; or:要求不高，只要满足一个条件就好 select email,last_name,salary,department_id from employees where salary >= 10000 or department_id=90; AND的优先级大于OR select last_name, job_id,salary from employees where job_id = ‘SA_REP’ OR job_id=‘AD_PRES’ and salary > 15000; select last_name, job_id,salary from employees where ( job_id = ‘SA_REP’ OR job_id=‘AD_PRES’ ) and salary > 15000;

ORDER BY排序

select last_name,first_name,hire_date from employees ORDER BY hire_date; 同上面一样 select last_name,first_name,hire_date from employees ORDER BY hire_date asc; 返着查询 查询后在排序 select last_name,first_name,department_id,employee_id from employees where department_id=90 ORDER BY employee_id; select last_name,first_name,department_id,employee_id from employees where department_id=90 ORDER BY employee_id desc; 默认空值排在最后 select last_name,first_name,commission_pct from employees ORDER BY commission_pct; 让空值排在前面 select last_name,first_name,commission_pct from employees ORDER BY commission_pct nulls FIRST; 列别名进行排序 select last_name,first_name m ,commission_pct from employees ORDER BY m; 使用表达式排序 select last_name,first_name,salary,salary+100 from employees ORDER BY salary+100; 多个列排序（先排序ID列，在排序first_name列，在按字母排序） select last_name,first_name,salary,department_id from employees ORDER BY department_id,first_name; 一个升序，一个降序（这两我不分） select last_name,first_name,salary,department_id from employees ORDER BY department_id asc ,first_name desc; 在select中按列号排序 select last_name,first_name,salary,department_id from employees ORDER BY 3; select last_name,first_name,salary,department_id from employees ORDER BY 4.3; 返回前几行 select employee_id,last_name,first_name from employees ORDER BY employee_id FETCH first 5 ROWS ONLY; 返回百分之n行 select employee_id,last_name,first_name from employees ORDER BY employee_id FETCH first 10 percent rows only;

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