单行子查询

 单行子查询：

#单行子查询：
#操作符：= ！= >   >=   <   <=

#题目：查询工资大于149号员工工资的员工信息
SELECT salary 
FROM employees
WHERE salary>(
               SELECT salary
               FROM employees
               WHERE employee_id='149'
               );
​

#返回job_id与141号员工相同，salary比143号员工多的员工姓名，job_id和工资
SELECT last_name,job_id,salary
FROM employees
WHERE job_id=(
               SELECT job_id
               FROM employees
               WHERE employee_id=141
              )
AND salary>(
           SELECT salary
           FROM employees
           WHERE employee_id=143
            );

#返回公司工资最少的员工的last_name,job_id和salary
SELECT last_name,job_id,salary
FROM employees
WHERE salary=(
             SELECT MIN(salary)
             FROM employees
             );

#查询与141号员工的manager_id和department_id相同的其他员工的employee_id， manager_id，department_id
SELECT employee_id,manager_id,department_id
FROM employees
WHERE manager_id=(
                  SELECT manager_id
                  FROM employees
                  WHERE employee_id =141
                  )
AND department_id=(
                   SELECT department_id
                   FROM employees
                   WHERE employee_id =141
                    )
AND employee_id != 141;

#查询最低工资大于50号部门最低工资的部门id和其最低工资
SELECT department_id,MIN(salary)
FROM employees
GROUP BY department_id
HAVING MIN(salary)>(
                   SELECT MIN(salary)
                   FROM employees
                   WHERE department_id=50
                   );

#显式员工的employee_id,last_name和location。
 其中，若员工department_id与location_id为1800 的department_id相同，
 则location为’Canada’，其余则为’USA’。
SELECT employee_id,last_name,
CASE department_id WHEN(SELECT department_id FROM departments WHERE location_id=1800) THEN 'Canada'                                                          

                                                                                     ELSE 'USA' END  "location"                                       
    FROM employees;