Question 21530 in Mysql Question posted in
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Why AND after a SET is not a syntax error in mysql?

I was surprised that this is not a syntax error:

UPDATE mytable  
SET deleted = 1 
AND name  = 'Cindy'

It doesn’t affect the result of the command, is there any use of adding an AND after a SET? Or mysqsl will just ignore it?

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2

Answers


  1. 0

    Because the expression:

    1 AND name  = 'Cindy'

    is a Boolean expression that evaluates to 0 for False or 1 for True
    and the value of this expression will be assigned to the column deleted, like:

    SET deleted = (1 AND (name = 'Cindy'))
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  2. 0

    The statement takes into account the operators precedence. And the query acts as

    UPDATE mytable  
SET deleted = (1 AND (name  = 'Cindy'))

    I.e. firstly the condition name = 'Cindy' is tested producing TRUE (1), FALSE (0) or NULL.

    Then the expression 1 AND {result} is evaluated.

    And finally the result of this expression evaluation is assigned into deleted column.

    DEMO fiddle

    If you receive the same result like for

    UPDATE mytable  
SET deleted = 1

    then name column value is equal to 'Cindy' using current collation.

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