PostgreSQL的子查詢一一對多的關係搜索

Question

employee_id | first_name | last_name 
-------------------------------------- 
00001   Tim   Smith 
00002   John   Doe 

employee_id | skill_id 
-------------------------------------- 
00001   1 
00001   2 
00002   1 
00002   3 

skill_id | name 
-------------------------------------- 
1   Java 
2   PHP 
3   MySQL 

我想與Java 和 PHP技能選擇所有員工。與我上面的示例應該返回

employee_id | first_name | last_name 
-------------------------------------- 
00001   Tim   Smith 

我怎麼能在PostgrSQL中做到這一點？

Answer 1

嘗試

SELECT e.employee_id, e.first_name, e.last_name 
    FROM employee e JOIN employee_skills es 
    ON es.employee_id = e.employee_id JOIN skills s 
    ON es.skill_id = s.skill_id 
WHERE s.name IN('PHP', 'Java') 
GROUP BY e.employee_id, e.first_name, e.last_name 
HAVING COUNT(DISTINCT s.skill_id) = 2 

如果在你的UI你已經知道skill_ids你可能會做，因爲你必須參考表，那麼你甚至不需要第二個連接

SELECT e.employee_id, e.first_name, e.last_name 
    FROM employee e JOIN employee_skills es 
    ON es.employee_id = e.employee_id 
WHERE es.skill_id IN(1, 2) 
GROUP BY e.employee_id, e.first_name, e.last_name 
HAVING COUNT(DISTINCT es.skill_id) = 2 

輸出：

 
| EMPLOYEE_ID | FIRST_NAME | LAST_NAME | 
---------------------------------------- 
|   1 |  Tim |  Smith | 

這裏是SQLFiddle demo