DESC employees;
SELECT * FROM employees;
SELECT last_name,salary*(1+IFNULL(commission_pct,0))*12 "ANUAL SALARY"
FROM employees;
SELECT DISTINCT job_id
FROM employees;
SELECT last_name , salary
FROM employees
WHERE salary>12000;
SELECT last_name,department_id
FROM employees
WHERE employee_id=176;
SELECT 12%5,12%3,12 MOD -5 ,12%-5
FROM DUAL;
SELECT employee_id,last_name , salary
FROM employees
WHERE employee_id%2=0;
SELECT 1<>2, 2=2,0='a',2<3,4>2,4>=4
FROM DUAL;
SELECT 1=NULL
FROM DUAL;
SELECT NULL=NULL
FROM DUAL;
SELECT NULL <=> NULL
FROM DUAL;
SELECT 'a'='b','ab'='ab'
FROM DUAL;
SELECT last_name,salary,department_id
FROM employees
WHERE salary=6000;
#① IS NULL \ IS NOT NULL \ ISNULL
SELECT last_name,salary,commission_pct
FROM employees
WHERE commission_pct <=> NULL
SELECT last_name,salary,commission_pct
FROM employees
WHERE commission_pct IS NULL
SELECT last_name,salary,commission_pct
FROM employees
WHERE commission_pct IS NOT NULL
#③ BETWEEN 条件下界1 AND 条件上界2 （查询条件1和条件2范围内的数据，包含边界）
SELECT last_name,salary,commission_pct,department_id
FROM employees
WHERE salary BETWEEN 6000 AND 8000;
SELECT last_name ,salary,commission_pct,department_id
FROM employees
WHERE salary>=6000 && salary <=8000;
#查询工资不在6000 到 8000的员工信息
SELECT last_name ,salary ,commission_pct,department_id
FROM employees
WHERE salary NOT BETWEEN 6000 AND 8000;
SELECT last_name ,salary,commission_pct,department_id
FROM employees
WHERE salary <6000 || salary > 8000;
#练习：查询部门为10,20,30部门的员工信息
SELECT last_name ,salary,commission_pct,department_id
FROM employees
WHERE department_id=10 OR department_id=20 OR department_id=30
#④ in (set)\ not in (set)
SELECT last_name,salary,commission_pct,department_id
FROM employees
WHERE department_id IN (10,20,30);
#练习：查询工资不是6000,7000,8000的员工信息
SELECT last_name,salary
FROM employees
WHERE salary NOT IN (6000,7000,8000);
#⑤ LIKE :模糊查询
# % : 代表不确定个数的字符 （0个，1个，或多个）
#练习：查询last_name中包含字符'a'的员工信息
SELECT last_name FROM employees
WHERE last_name LIKE '%a%';
#查询last_name中以字符'a'开头的员工信息\
SELECT last_name
FROM employees
WHERE last_name LIKE 'a%';
#练习：查询last_name中包含字符'a'且包含字符'e'的员工信息
SELECT last_name
FROM employees
WHERE last_name LIKE '%a%' AND last_name LIKE '%e%';
# _ ：代表一个不确定的字符
#练习：查询第3个字符是'a'的员工信息
SELECT last_name ,salary,department_id
FROM employees
WHERE last_name LIKE '__a%';
#练习：查询第2个字符是_且第3个字符是'a'的员工信息
SELECT last_name
FROM employees
WHERE last_name LIKE '_\_a%';
#⑥ REGEXP \ RLIKE :正则表达式
SELECT last_name
FROM employees
WHERE last_name REGEXP '^Ki';
SELECT last_name
FROM employees
WHERE last_name RLIKE 'a$';
#3. 逻辑运算符： OR || AND && NOT ! XOR
#查找部门ids是10或者20的员工信息
SELECT last_name ,department_id
FROM employees
WHERE department_id=10 OR department_id=20;
SELECT last_name ,department_id
FROM employees
WHERE department_id=10 || department_id=20;
#查找部门里面ID 50 ,且薪资大于6000的员工信息
SELECT last_name ,department_id
FROM employees
WHERE department_id=50 AND salary >6000;
SELECT last_name ,department_id
FROM employees
WHERE department_id=50 && salary >6000;
