VARCHAR型
With CHAR the same type, VARCHAR type also used data type (string type) specified storage column of the string, the string may be specified length (maximum length) by a number in parentheses. But this type of column is a variable-length string form to hold the string .
Complement fixed-length string of characters when the number has not reached the maximum length of a half-size space, but a different variable length strings, even if the number of characters has not reached the maximum length, is not made up with a half-size space. For example, we have to VARCHAR (8) of the input string type column of ' ABC ' of the time, the string is stored ' ABC ' .
The type of character string stored in the column and also CHAR types, is case-sensitive.
Set constraint
constraint other than the data type, the data stored in a column or adding a function of limiting conditions. Product table set two restrictions. 
In addition, create Product tables CREATE TABLE behind the statement, there is such a description below. 
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