笛卡爾積錯誤:多表查詢必須有連線條件，否則會產生笛卡爾積錯誤，得到資料條數=每個表資料條數的積
select last_name,employees.department_id, department_name from employees, departments內連線：合併具有同一列的兩個以上的表的行, 結果集中不包含乙個表與另乙個表不匹配的行
等值連線（兩個表）
select last_name,e.department_id, department_name from employees e, departments d where e.department_id = d.department_idselect last_name,e.department_id, department_name,l.city from employees e, departments d, locations l where e.department_id = d.department_id and d.location_id = l.location_id非等值連線：
select employee_id,last_name,salary,grade_level from employees e,job_grades j where e.salary between j.lowest_sal and j.highest_sal查詢公司中員工『chen』的manager資訊：
select emp.last_name,manager.last_name,manager.salary,manager.email from employees emp, employees manager
where emp.manager_id = manager.employee_id and lower(emp.last_name)
='chen'
左外連線：
select last_name,e.department_id, department_name from employees e, departments d where e.department_id = d.department_id(
+)
select last_name,e.department_id, department_name from employees e, departments d where e.department_id(+)
= d.department_id
自然連線(natural join)：自動連線兩個表中所有相同的字段，查詢的欄位名不能使用限定詞
select last_name,department_id, department_name from employees e natural
join departments d
select last_name,department_id, department_name from employees e join departments d using
(department_id)
select last_name,e.department_id, department_name from employees e join departments d on e.department_id = d.department_idselect last_name,e.department_id, department_name,l.city from employees e
join departments d on e.department_id = d.department_id
join locations l on d.location_id = l.location_id
左外關聯：
select last_name,e.department_id, department_name from employees e left
outer
join departments d on e.department_id = d.department_id
select last_name,e.department_id, department_name from employees e right
outer
join departments d on e.department_id = d.department_id
select last_name,e.department_id, department_name from employees e full
outer
join departments d on e.department_id = d.department_id
顯示所有員工的姓名，部門號和部門名稱。
select last_name,e.department_id,department_name
from employees e, departments d
where e.department_id = d.department_id(+)
;
select
distinct job_id,location_id
from employees e left
join departments d
on e.department_id = d.department_id
where d.department_id =
90
select last_name,department_name,d.location_id,city
from employees e
join departments d on e.department_id = d.department_id
join locations l on d.location_id = l.location_id
where e.commission_pct is
notnull
;
select last_name,job_id,e.department_id,department_name
from employees e
join departments d on e.department_id = d.department_id
join locations l on d.location_id = l.location_id
where l.city =
'toronto'
;
select e1.last_name "employees"
,e1.employee_id "emp#"
,e2.last_name "manager"
,e2.employee_id "mgr#"
from employees e1,employees e2
where e1.manager_id = e2.employee_id(+)
;
多表查詢 多表查詢 多表查詢
查詢語法 select 列表名稱 from 表明列表 where 笛卡爾積 有兩個集合a，b，取這兩個集合的所有組成情況 要完成多表查詢，需要消除無用的資料 多表查詢分類 1 內連線查詢 1 隱式內連線 使用where消除無用的資料 例子 select t1.name,t1.gender,t2.na...
mysql 多表查詢or MySQL 多表查詢
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此時你得使用鏈結條件。通過存在於相對應列中的公共值，乙個表中的資料可以被另乙個表的資料鏈結，通常都是主鍵和外來鍵進行鏈結。一般鏈結條件寫在where子句裡。select empno,emp.deptno,loc from emp,dept where emp.deptno dept.deptno 對...