Question

我是一名软件开发人员。我有一个问题：如何使用select和join访问多个表？

主表的名称如下：

logs_0215
logs_0315

logs_mmyy  ->  m = month; y = year

时间戳表的名称如下：

timestamp_0215
timestamp_0315

timestamp_mmyy  ->  m = month; y = year

我的查询仅适用于一个表格，如：

SELECT a.id, b.stamp, c.name AS portal, d.name AS company, e.name AS protocol, a.value
FROM logs_0315 AS a
LEFT JOIN timestamp_0315 AS b ON a.time_id = b.id
LEFT JOIN portale AS c ON a.portal_id = c.id
LEFT JOIN companies AS d ON a.comp_id = d.id
LEFT JOIN proocols AS e ON a.prot_id = e.id
WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'

如何访问包含logs_mmyy及其时间戳的所有表？

提前感谢您的帮助。

你诚挚的 t.koelpin

Answer 1

您必须明确标识每个表格;必须在FROM子句中按名称标识每个表。 SQL不支持标识符（表名，列名等）的通配符模式匹配。

根据您发布的内容，看起来您可以使用UNION ALL集合运算符将多个SELECT语句的结果合并为一个查询：

  SELECT a.id, ...
    FROM logs_0315 a 
    LEFT JOIN timestamp_0315 AS b ON a.time_id = b.id
         ...
   WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'
  UNION ALL
  SELECT a.id, ...
    FROM logs_0415 a 
    LEFT JOIN timestamp_0415 AS b ON a.time_id = b.id
         ...
   WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'
  UNION ALL
  SELECT a.id, ...
    FROM logs_0515 a 
    LEFT JOIN timestamp_0515 AS b ON a.time_id = b.id
         ...
   WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'

如果您需要对合并结果ORDER BY，则可以将每个SELECT语句括在parens中。像这样：

 ( SELECT a.id, ...
     FROM logs_0315 a 
     LEFT JOIN timestamp_0315 AS b ON a.time_id = b.id
          ...
    WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'
 )
 UNION ALL
 ( SELECT a.id, ...
     FROM logs_0415 a 
     LEFT JOIN timestamp_0415 AS b ON a.time_id = b.id
          ...
    WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'
 )
 UNION ALL
 ( SELECT a.id, ...
     FROM logs_0515 a 
      LEFT JOIN timestamp_0515 AS b ON a.time_id = b.id
          ...
    WHERE b.stamp BETWEEN '2015-05-01' AND '2015-06-25'
 )
 ORDER BY ...

为了使其动态化，要获取模式logs_mmyy的所有表，您可以查询information_schema.tables并获取表的列表，然后使用它来动态生成上述语句。此方法需要（至少）两个单独的SQL语句。在单个SQL语句中无法实现此类型的结果。

MySQL具有月度表和每月联接

1 个答案: