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Implicit automatic casting

suggest change 
select '123' * 2;

To make the multiplication with 2 MySQL automatically converts the string 123 into a number.

Return value:

246

The conversion to a number starts from left to right. If the conversion is not possible the result is 0 

select '123ABC' * 2

Return value:

246 
select 'ABC123' * 2

Return value:

0
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Data Types:
* VARCHAR255 -- or not
* INT as AUTO INCREMENT
* Others
* Introduction numeric
* Integer Types
* Fixed Point Types
* Floating Point Types
* Bit Value Type
* CHARn
* DATE DATETIME TIMESTAMP YEAR and TIME
* Implicit automatic casting
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