dpkajqd31574096 2014-03-24 22:19
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MySql或语句在功能上没有意义

Why is it that the MySql "or" operator behaves like an "and" operator?

Example:

mysql>SELECT * FROM employee_tbl 
    ->WHERE daily_typing_pages= 250 OR  
    ->daily_typing_pages= 220 OR  daily_typing_pages= 170; 
+------+------+------------+--------------------+
| id   | name | work_date  | daily_typing_pages |
+------+------+------------+--------------------+
|    1 | John | 2007-01-24 |                250 |
|    2 | Ram  | 2007-05-27 |                220 |
|    3 | Jack | 2007-05-06 |                170 |
|    4 | Jill | 2007-04-06 |                220 |
+------+------+------------+--------------------+

why does it select all 3 records. Shouldn't it return the first match and be done with it? My mind right now is telling me that the "and" operator is the one that should by nature return all 3 rows. This behavior is different than how programming languages like PHP work. Any references to official documentation would be helpful or links to how the OR and the AND work would help too.

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  • dongxixia6399 2014-03-24 22:21
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    No, just read the query out loud like this.

    I want everything from my employee table if daily typing pages is 250, or if daily typing pages is 220, or if daily typing pages is 170.

    If you told me to get you all drinks from 7-11 that are either orange, blue, or green. I'd bring you back all those drinks.

    If you want to limit, you need to explicitly state it:

    SELECT * FROM employee_tbl 
        ->WHERE daily_typing_pages= 250 OR  
        ->daily_typing_pages= 220 OR  daily_typing_pages= 170 LIMIT 1; 
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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