All matter is made of atoms. Atoms are the smallest particle of matter. They are so small that you cannot see them with your eyes or even with a standard microscope. A standard sheet of paper is about a million atoms thick.
Answer Wiki. The int type is a 4-byte signed integer. There are also tinyint (1 byte), smallint (2 bytes), and bigint (8 bytes), and unsigned versions of all of these. As Apostolos mentioned, the docs for all the numeric types are here: http://dev.mysql.com/doc/refman/...
The above both MySql table create statements with PRIMARY KEY and UNIQUE Constraint are prevent or restrict duplicate entries in a user_info table. When you do this the indexed columns must be NOT. Because the PRIMARY KEY or UNIQUE Constraint never allow NULL values in these fields. Use INSERT IGNORE instead of INSERT.