如何从连接的MySQL表中进行选择？

我基本上有两张桌子：

A(id int, name varchar(10), info varchar(10))
B(id int, item varchar(10))

A
1 A Hello
2 B World
3 C Foo

B
1 apple
1 orange
1 hammer
2 glass
2 cup

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

正在使用以下查询

mysql> SELECT a.id, a.name, a.info, group_concat(b.item SEPARATOR ' ')
       FROM a
       LEFT OUTER JOIN b ON (a.id=b.id)
       GROUP BY 1,2,3;

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

我得到了期望的输出：

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

现在我想修改查询以获得一个结果表，该表包含相同的信息，但只包含以字母o开头的项目，

（如“o%”）

如何获得以下输出

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                |                        
+------+------+-------+------------------------------------+

请注意，我仍然希望显示整个字符串

'apple orange hammer'

，而不仅仅是

'orange'

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

SELECT a.id, a.name, a.info, group_concat(b.item SEPARATOR ' ')
FROM a
LEFT OUTER JOIN b ON (a.id=b.id)
WHERE a.id in (select id from b where upper(SUBSTRING(b.item,0,1)) = 'O')
GROUP BY 1,2,3

---

我怀疑这是否能很好地执行，但在我看来这似乎是合乎逻辑的。

在group by之后，您需要在group_concat上使用不得不执行的like运算符

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

Group By 1,2,3
HAVING group_concat(b.item SEPARATOR ' ') like ('%o%')

---

请注意，我正在寻找您需要调整类似声明以符合您的要求的任何o。

还有另一种方法：

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+

SELECT a.id, a.name, a.info, group_concat(b.item SEPARATOR ' ') AS items
   FROM a
   LEFT OUTER JOIN b ON (a.id=b.id)
   GROUP BY 1,2,3
   HAVING items REGEXP '[[:<:]]o';

选择a.id、a.name、a.info、group_concat（b.项目分隔符“”）作为项目
从
左外连接b打开（a.id=b.id）
按1,2,3分组
具有项REGEXP'[]：
如果在
b（item，id）

+------+------+-------+------------------------------------+
| id   | name | info  | group_concat(b.item separator ' ') |
+------+------+-------+------------------------------------+
|    1 | A    | Hello | apple orange hammer                | 
|    2 | B    | World | glass cup                          | 
|    3 | C    | Foo   | NULL                               | 
+------+------+-------+------------------------------------+