出現了一種情況，我必須啟發式地從公共 ID 中找出表名。這些表具有相同的確切結構，所以我認為union或union all會按照這里的一些答案的建議作業。問題是，對查詢應用限制子句效果不佳。如果我將其應用于多個選擇查詢，則會失敗；如果在 one 上，它只會將該表作為主要過濾器進行過濾。即使如下所示包裝它也不會產生所需的結果 - 即：將每個單獨查詢的回傳結果限制為一行。
重申問題：我如何知道已知表的串列是否具有特定值（命名列）？
開放選項提供了良好的表源作為別名，但禁止多重限制；結果可能很多：
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'
僅在第一個表結果上找到包裝選項過濾器；我們需要所有具有該值的表。
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
uj5u.com熱心網友回復：
如果您只想要表名，那么您的每個查詢都應該只回傳第一列：
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，以逗號分隔的字串形式獲取結果：
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 將過濾掉重復項。
轉載請註明出處，本文鏈接：https://www.uj5u.com/caozuo/394501.html