Question

我有以下3个SQL表：

    mysql> select * FROM borrower;
+--------+------------+---------+--------------+
| cardno | name       | address | phone        |
+--------+------------+---------+--------------+
|      1 | A          | nj,usa  | 111-222-333 |
|      2 | B          | NY,USA  | 444-555-666 |
|      3 | C          | nj,usa  | 777-888-999 |
+--------+------------+---------+--------------+
3 rows in set (0.00 sec)

mysql> select * FROM bookloans;
+--------+----------+--------+------------+------------+
| bookid | branchid | cardno | dateout    | duedate    |
+--------+----------+--------+------------+------------+
|      1 |        1 |      1 | 2014-04-01 | 2014-08-01 |
|      2 |        1 |      1 | 2014-04-02 | 2014-08-02 |
|      3 |        2 |      2 | 2014-04-04 | 2014-07-05 |
+--------+----------+--------+------------+------------+
1 row in set (0.00 sec)

    mysql> select * FROM books;
+--------+------------+---------+------
| bookid | title      | publishername | 
+--------+------------+---------+------
|      1 | Atitle     | tmh           |
|      2 | Btitle     | tmh           |
|      3 | Ctitle     | tmh           |
+--------+------------+---------+-----+
3 rows in set (0.00 sec)

mysql> select * FROM librarybranch;
+----------+------------+--------+
| branchid | branchname | address|
+--------+----------+--------+---+
|        1 | abc loc    | nj,usa  |
|        2 | def loc    | NY,USA  |
+----------+------------+---------+
2 rows in set (0.00 sec)

现在我想执行一个查询，显示书名，借用人姓名，借款人地址每本书由“def loc”分支借出，其分支是今天（2014-07-05）。我上来了有两个可能的查询：

1.基于联接的查询：

select books.title,borrower.name,librarybranch.branchname from (( bookloans inner join  
borrower on bookloans.cardno = borrower.cardno) inner join books on bookloans.bookid = 
books.bookid inner join librarybranch on bookloans.branchid=librarybranch.branchid) 
where duedate='2014-07-05' and branchname="def loc";

2.基于多个ands的查询：

select b.title,r.name,r.address from books b,borrower r,bookloans bl,librarybranch lb 
where lb.branchname='def loc' and lb.branchid = bl.branchid and bl.duedate='2014-07-05' 
and bl.cardno=r.cardno and bl.bookid=b.bookid;

对我来说，基于联接的查询是最直观的，我们正在创建一个巨型表，其中来自不同表的所有行连接在一起，然后基于来自多个表的列查询这个巨型表。但是我发现基于多个ands的查询给出相同的结果令人惊讶。我的问题是上面的选项2（一个基于多个ands）完全等同于选项1（执行内部联接）。如果没有，有什么区别？在这种情况下，它们似乎给出了相同的结果。

内连接与多个ands之间的区别

0 个答案: