Question

我继承了一个数据库，该数据库已被用来挖掘数据。有2个表是松散关联的-atm和dslams。 atm表包含与dslams“主机名”字段相关的“远程名”，“ rst”和“ CardNumber”字段。 atm表包含dslam卡的端口信息，而dslams表包含有关dslam卡本身的信息。我的任务是打印出所有具有特定类型卡（dslams.model =“ 6256”）的位置（dslams.name）以及该卡上具有特定服务水平的所有端口的数量（ atm.speed LIKE“ RI _％％09”或atm.speed LIKE“ RI ％％1 ％”）。我精心制作了以下几乎可以奏效的语句...

SELECT distinct(dslams.name) AS Remote, Count(atm.speed) AS Customers, dslams.model
FROM dslams
LEFT JOIN atm
ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
GROUP BY dslams.name
HAVING dslams.model="6256"
ORDER BY dslams.name;

这会精确打印出我需要的位置（除了1个位置）。

即。

MariaDB [dsl]> SELECT distinct(dslams.name) AS Remote, Count(atm.speed) AS Customers, dslams.model
    -> FROM dslams
    -> LEFT JOIN atm
    -> ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
    -> GROUP BY dslams.name
    -> HAVING dslams.model="6256"
    -> ORDER BY dslams.name;
+---------+-----------+-------+
| Remote  | Customers | model |
+---------+-----------+-------+
| ANTH-C2 |         1 | 6256  |
| BETY-C2 |         1 | 6256  |
| BHOT-C2 |         6 | 6256  |
| BNSH-C2 |         1 | 6256  |
| BUG2-C2 |         1 | 6256  |
| CCRK-C2 |         0 | 6256  |
...
| STLN-C2 |         1 | 6256  |
| SUMR-C2 |         2 | 6256  |
...
| WGRV-C2 |         0 | 6256  |
+---------+-----------+-------+
63 rows in set (0.34 sec)

由于某种原因，其中一个位置未被计数-STWL-C2。

MariaDB [dsl]> SELECT distinct(name), model FROM dslams WHERE model="6256" order by name;
+---------+-------+
| name    | model |
+---------+-------+
| ANTH-C2 | 6256  |
| BETY-C2 | 6256  |
| BHOT-C2 | 6256  |
| BNSH-C2 | 6256  |
| BUG2-C2 | 6256  |
| CCRK-C2 | 6256  |
...
| STWL-C2 | 6256  |
...
| WGRV-C2 | 6256  |
+---------+-------+
64 rows in set (0.00 sec)

STWL-C2位置与其他位置之间的表没有区别，因此应打印为0。

有人可以帮我弄清楚为什么错过这1个位置吗？

任何帮助或指导都将不胜感激，因为我是一名菜鸟SQL程序员，她试图尽我所能来理解这一点。

最好的问候，乔

Answer 1

不要使用HAVING dslams.model = '6256'，将其放在WHERE子句中。当您使用HAVING时，它将过滤之后分组。按name分组时，结果可以包含该分组中任何行的model，并且不一定选择model = '6256'。

SELECT dslams.name AS Remote, Count(atm.speed) AS Customers, dslams.model
FROM dslams
LEFT JOIN atm
ON (dslams.hostname = CONCAT(atm.remotename,'-',atm.rst,'-S',atm.CardNumber)) AND (atm.speed LIKE "RI_%_%09" OR atm.speed LIKE "RI_%_%1_%")
WHERE dslams.model = '6256'
GROUP BY dslams.name
ORDER BY dslams.name;

mysql语句的99％工作行为需要为100％

1 个答案: