-- 子查詢
-- 先根據"湯姆"查詢出對應的部門編號！
select dept_id from tb_emp where emp_name = '湯姆';
-- 在部門資訊表，根據部門編號查詢部門名稱！
select dept_name from tb_dept where dept_id = 101;
-- 組合
select dept_name from tb_dept where dept_id = (
        select dept_id from tb_emp where emp_name = '湯姆'
);
-- 查詢“cat”在10月份工資情況！
-- 先根據"cat"查詢對應的員工編號
 

select emp_id from tb_emp where emp_name = 'cat';
-- 根據員工編號2查詢工資情況
select * from tb_salary where s_put_time = '2022-10-10' and emp_id = 2;
-- 組合
select * from tb_salary where s_put_time = '2022-10-10' and emp_id = (
        select emp_id from tb_emp where emp_name = 'cat'
);
-- 查詢“湯姆”和“cat”相同部門的員工資訊！
-- 根據“湯姆”和“cat”查詢對應的部門編號
 

select dept_id from tb_emp where emp_name = '湯姆' or emp_name ='cat';
-- 根據部門編號查詢員工資訊
select * from tb_emp where dept_id = 101;
-- 當子查詢返回是多個結果集！ 使用in
select * from tb_emp where dept_id in (
        select dept_id from tb_emp where emp_name = '湯姆' or emp_name ='cat'
);

-- 子查詢當做臨時表來使用！
select * from tb_emp e, tb_salary s where
 
 e.emp_id = s.s_id order by dept_id;
select * from (
        select e.*,s.s_put_time,s.s_salary,s.s_state from tb_emp e, tb_salary s where e.emp_id = s.s_id
)tab where tab.s_put_time > '2022-10-01';
-- 檢視每個部門最高工資的員工資訊
-- 根據部門來分組，獲取最高工資
select e.dept_id,max(s.s_salary) from tb_emp e, tb_salary s where e.emp_id = s.emp_id
group by e.dept_id;
-- 根據部門編號和工資查詢員工資訊
select e.* from tb_emp e, tb_salary s where e.emp_id = s.emp_id
and e.dept_id = 101 and s.s_salary = 60000;
-- 合併
select e.* from tb_emp e, tb_salary s,(
        select e.dept_id,max(s.s_salary) maxsal from tb_emp e, tb_salary s where e.emp_id = s.emp_id
        group by e.dept_id
)tab where e.emp_id = s.emp_id and e.dept_id = tab.dept_id and s.s_salary = tab.maxsal;
-- 檢視每個部門最高工資的員工資訊 --> any
select e.* from tb_emp e, tb_salary s where e.emp_id = s.emp_id
and (e.dept_id,s.s_salary) = any (
        select e.dept_id,max(s.s_salary) from tb_emp e, tb_salary s where e.emp_id = s.emp_id
        group by e.dept_id
);

-- 臨時列使用
select e.*,(
        select dept_name from tb_dept where dept_id = e.dept_id) deptName
from tb_emp e;