Question

我有两张桌子。

表db1 AND db2

DB1
+-----------+------------+
|    id     |    nameDb  |
+-----------+------------+
|    1      |    name1   |
+-----------+------------+
|    2      |    name2   |
+-----------+------------+
|    3      |    name3   |
+-----------+------------+

DB2

+------------+------------+-------------+----------------------+
|    id      |   name     |   id_db1    |          date        |
+------------+------------+-------------+----------------------+
|    1       |   test1    |      1      |  2013-05-10 10:00:00 |
+------------+------------+-------------+----------------------+
|    2       |   test2    |      1      |  2013-05-10 11:00:00 |
+------------+------------+-------------+----------------------+
|    3       |   test3    |      1      |  2013-05-10 11:10:00 |
+------------+------------+-------------+----------------------+
|    4       |   test4    |      1      |  2013-05-10 11:40:00 |
+------------+------------+-------------+----------------------+

我的疑问是：

SELECT a.nameDb, b.name FROM db1 a 
LEFT JOIN db2 b ON b.id_db1 = a.id 
WHERE DATE_FORMAT(b.name, '%Y-%m-%d') = '2013-05-10'

我需要返回与当天相关的所有内容，这些相关内容也必须出现......

喜欢的东西

+------------+------------+
|    nameDb  |   name     |
+------------+------------+
|    name1   |   test1    |
+------------+------------+
|    name1   |   test2    |
+------------+------------+
|    name1   |   test3    |
+------------+------------+
|    name1   |   test4    |
+------------+------------+
|    name2   |   NULL     |
+------------+------------+
|    name3   |   NULL     |
+------------+------------+

任何想法？

Answer 1

试试这个

SELECT a.nameDb, b.name FROM db1 a 
LEFT JOIN db2 b ON b.id_db1 = a.id 
and DATE_FORMAT(b.date, '%Y-%m-%d') = '2013-05-10'

如果在where子句中使用左外连接表中的列，则其行为类似于内连接

Answer 2

你想要一个outer join。这里有不同连接及其输出的良好描述：What is the difference between "INNER JOIN" and "OUTER JOIN"?

Answer 3

您应该只需要一个RIGHT JOIN或交换表格就可以使用LEFT JOIN

SELECT a.nameDb, b.name 
FROM db1 a 
  RIGHT JOIN db2 b ON b.id_db1 = a.id AND DATE_FORMAT(b.name, '%Y-%m-%d') = '2013-05-10'

Answer 4

您应该将WHERE更改为AND，以便将日期检查作为连接条件的一部分：

SELECT a.nameDb, b.name FROM db1 a 
LEFT JOIN db2 b ON b.id_db1 = a.id 
AND DATE_FORMAT(b.name, '%Y-%m-%d') = '2013-05-10'

在mysql中的子句

4 个答案: