Optimizing datatypes

You should define tables such that they occupy minimum space on disk while accommodating all possible values.

If the size is smaller:

• Less data is written to or read from the disk, which makes queries faster.
• The contents on the disk are loaded to the main memory while processing queries. So, smaller tables occupy less space in the main memory.
• Less space is occupied by indexes.

How to do it...

1. If you want to store an employee number, for which the maximum possible value is 500,000, the optimum datatype is MEDIUMINT UNSIGNED (which occupies 3 bytes). If you are storing it as INT, which occupies 4 bytes, you are wasting a byte for each row.
2. If you want to store the first name, for which the length is varying and the maximum possible value is 20, it is optimal to declare it as varchar(20). If you are storing it as char(20), and just a few names are 20 characters long while the remaining are less than 10 characters long, you are wasting space of 10 characters.
3. While declaring varchar...