CAST allows you to convert from one type to another.
Often a CAST is implicit - for example if you concatenate
a string with a number the number will be automatically changed to
a string. However sometimes you need to make the CAST explicit.
CAST(expr TO type)
In this example we get the population in millions by casting
the floating point value to DECIMAL(8,1) - this ensures one
decimal place of accuracy.
You can also CAST a date to a string to extract components using
SUBSTRING or make up another date.
