多次 Table 搜索，使用 Limit 子句和已知结果源 Table 名称

Question

出现了一种情况，我必须从一个公共 ID 中试探性地找出一个 table 名称。 tables 具有完全相同的结构，所以我认为 union 或 union all 将按照此处一些答案的建议工作。问题是，对查询应用 limit 子句 效果不佳。如果我将它应用于 多个 select 查询 ，它会失败；如果 在一个 上，它只过滤那个 table 作为主要。即使 包装它 如下所示也没有产生所需的结果 - 即：将每个单独查询的返回结果限制为一行.

重述问题：我如何知道已知 table 的列表是否具有特定值（命名列）？

一个开放的选项提供了很好的 table 来源作为别名，但禁止多重限制；结果可能很多：

SELECT `ID`, `BATCH_NUMBER`, 'TBL1' AS 'table_one' FROM `table_one` WHERE `NAMED_ID` = '123' 
UNION ALL
SELECT `ID`, `BATCH_NUMBER`, 'TBL2' AS 'table_two' FROM `table_two` WHERE `NAMED_ID` = '123' 
UNION ALL
SELECT `ID`, `BATCH_NUMBER`, 'TBL3' AS 'table_three' FROM `table_three` WHERE `NAMED_ID` = '123'

仅在找到前 table 个结果时包装选项过滤器；我们需要所有 table 的值。

select * from (
SELECT `ID`, `BATCH_NUMBER`, 'TBL1' AS 'table_one' FROM `table_one` WHERE `NAMED_ID` = '123' 
UNION ALL
SELECT `ID`, `BATCH_NUMBER`, 'TBL2' AS 'table_two' FROM `table_two` WHERE `NAMED_ID` = '123' 
UNION ALL
SELECT `ID`, `BATCH_NUMBER`, 'TBL3' AS 'table_three' FROM `table_three` WHERE `NAMED_ID` = '123' 
) as resutl_table  
LIMIT 1

Answer 1

如果您只想要 table 个名称，那么您的每个查询都应该 return 只在第一列：

SELECT 'TBL1' AS table_name FROM `table_one` WHERE `NAMED_ID` = '123' 
UNION
SELECT 'TBL2' AS table_name FROM `table_two` WHERE `NAMED_ID` = '123' 
UNION
SELECT 'TBL3' AS table_name FROM `table_three` WHERE `NAMED_ID` = '123'

或者，获取以逗号分隔的字符串形式的结果：

SELECT GROUP_CONCAT(table_name) AS table_names
FROM (
  SELECT 'TBL1' AS table_name FROM `table_one` WHERE `NAMED_ID` = '123' 
  UNION
  SELECT 'TBL2' AS table_name FROM `table_two` WHERE `NAMED_ID` = '123' 
  UNION
  SELECT 'TBL3' AS table_name FROM `table_three` WHERE `NAMED_ID` = '123'
) t

UNION 将过滤掉重复项。

多次 Table 搜索，使用 Limit 子句和已知结果源 Table 名称

Multiple Tables Search, with Limit Clause and Known Result Source Table Names

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sql-limit