MySQL选择另一行(如果不存在)

问题描述：

我需要从表中选择具有特定ID的行，但是如果该行不存在，则需要选择第一行.可以在单个查询中做到吗?

I need to select a row from the table with the specific id, but if the row doesn't exist I need to select the first row. is it possible to do it in a single query?

示例: 我有一个带有ID和文本字段的表格.我在表中有3行

example: I have a table with an id and text fields. and I have 3 rows in the table

id    txt
----------------
1     text1
2     text2
3     text3

如果说SELECT * FROM myTable WHERE id = 4不存在，我需要选择第一行，否则请选择ID为4的行.

I need to select the first row if say SELECT * FROM myTable WHERE id = 4 doesn't exist Else select the row with id 4.

答

尝试一下:

SELECT * FROM 
   (SELECT * FROM your_table
      WHERE id = your_id
      LIMIT 1
    UNION
    SELECT * FROM your_table
      LIMIT 1) a
LIMIT 1

想法是先取得所需的行，然后追加到这一行，最后取得第一行.如果所需的行不存在，将选择第一个...

The idea is to take first desired row and appending to this very first row, finally taking first one. If desired row does not exists, first one will be selected...

MySQL选择另一行(如果不存在)

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