mysql兩表聯合查詢的四種情況
阿新 • • 發佈:2019-01-03
一般來說,我們為了得到更完整的結果,我們需要從兩個或更多的表中獲取結果,我一般都是用select xxx,xxx from 表1,表2 where 表1.xxx=表2.xxx,我們一般都是進行的是這般的操作,其實mysql中還有一種操作,那就是join的操作,例如底下有兩個表:
請看 "Persons" 表:
Id_P | LastName | FirstName | Address | City |
---|---|---|---|---|
1 | Adams | John | Oxford Street | London |
2 | Bush | George | Fifth Avenue | New York |
3 | Carter | Thomas | Changan Street | Beijing |
接下來請看 "Orders" 表:
Id_O | OrderNo | Id_P |
---|---|---|
1 | 77895 | 3 |
2 | 44678 | 3 |
3 | 22456 | 1 |
4 | 24562 | 1 |
5 | 34764 | 65 |
以上的這兩個表,然後我們把它們進行連線查詢
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons, Orders
WHERE Persons.Id_P = Orders.Id_P
結果集:
LastName | FirstName | OrderNo |
---|---|---|
Adams | John | 22456 |
Adams | John | 24562 |
Carter | Thomas | 77895 |
Carter | Thomas | 44678 |
如果使用關鍵詞JOIN來從兩個表中獲取資料
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON Persons.Id_P = Orders.Id_P
ORDER BY Persons.LastName
結果集:
LastName | FirstName | OrderNo |
---|---|---|
Adams | John | 22456 |
Adams | John | 24562 |
Carter | Thomas | 77895 |
Carter | Thomas | 44678 |
不同的 SQL JOIN
- JOIN: 如果表中有至少一個匹配,則返回行
- LEFT JOIN: 即使右表中沒有匹配,也從左表返回所有的行
- RIGHT JOIN: 即使左表中沒有匹配,也從右表返回所有的行
- FULL JOIN: 只要其中一個表中存在匹配,就返回行
LEFT JOIN 關鍵字語法
"Persons" 表:
Id_P | LastName | FirstName | Address | City |
---|---|---|---|---|
1 | Adams | John | Oxford Street | London |
2 | Bush | George | Fifth Avenue | New York |
3 | Carter | Thomas | Changan Street | Beijing |
"Orders" 表:
Id_O | OrderNo | Id_P |
---|---|---|
1 | 77895 | 3 |
2 | 44678 | 3 |
3 | 22456 | 1 |
4 | 24562 | 1 |
5 | 34764 | 65 |
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo FROM Persons LEFT JOIN Orders ON Persons.Id_P=Orders.Id_P ORDER BY Persons.LastName
結果集:
LastName | FirstName | OrderNo |
---|---|---|
Adams | John | 22456 |
Adams | John | 24562 |
Carter | Thomas | 77895 |
Carter | Thomas | 44678 |
Bush | George |
SQL RIGHT JOIN 關鍵字
"Persons" 表:
Id_P | LastName | FirstName | Address | City |
---|---|---|---|---|
1 | Adams | John | Oxford Street | London |
2 | Bush | George | Fifth Avenue | New York |
3 | Carter | Thomas | Changan Street | Beijing |
"Orders" 表:
Id_O | OrderNo | Id_P |
---|---|---|
1 | 77895 | 3 |
2 | 44678 | 3 |
3 | 22456 | 1 |
4 | 24562 | 1 |
5 | 34764 | 65 |
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo FROM Persons RIGHT JOIN Orders ON Persons.Id_P=Orders.Id_P ORDER BY Persons.LastName
結果集:
LastName | FirstName | OrderNo |
---|---|---|
Adams | John | 22456 |
Adams | John | 24562 |
Carter | Thomas | 77895 |
Carter | Thomas | 44678 |
34764 |
SQL FULL JOIN 關鍵字
"Persons" 表:
Id_P | LastName | FirstName | Address | City |
---|---|---|---|---|
1 | Adams | John | Oxford Street | London |
2 | Bush | George | Fifth Avenue | New York |
3 | Carter | Thomas | Changan Street | Beijing |
"Orders" 表:
Id_O | OrderNo | Id_P |
---|---|---|
1 | 77895 | 3 |
2 | 44678 | 3 |
3 | 22456 | 1 |
4 | 24562 | 1 |
5 | 34764 | 65 |
全連線(FULL JOIN)例項
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo FROM Persons FULL JOIN Orders ON Persons.Id_P=Orders.Id_P ORDER BY Persons.LastName
結果集:
LastName | FirstName | OrderNo |
---|---|---|
Adams | John | 22456 |
Adams | John | 24562 |
Carter | Thomas | 77895 |
Carter | Thomas | 44678 |
Bush | George | |
34764 |