Question

我需要从表格中选择一行,具体地说,但如果增长没有,我需要选择第一行。在单一询问中是可能的?

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

我需要选择第一行,如果说<条码>。 exist Else 用背书4选择行。

Answer 1

为此:

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

想法是首先投入使用,并首先投入使用。如果没有所希望的行文,将首先选定一条。

Answer 2

SELECT * FROM (
   SELECT * FROM table1 WHERE [..your criteria...] LIMIT 1
   UNION
   SELECT * FROM table1 LIMIT 1    
) LIMIT 1

Answer 3

Here there is another way that may be considered

SELECT * FROM table1  
WHERE [criteria 1] AND [criteria 2]  

UNION 

SELECT * FROM table1  
WHERE [criteria 1] AND NOT EXISTS 
(
   SELECT * FROM table1  
   WHERE [criteria 1] AND [criteria 2]    
)

LIMIT 1;

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