The main type for expressing Haskell values to SQL databases.
This type is used to marshall Haskell data to and from database APIs.
HDBC driver interfaces will do their best to use the most accurate and
efficient way to send a particular value to the database server.
Values read back from the server are put in the most appropriate SqlValue
type. fromSql can then be used to convert them into whatever type
is needed locally in Haskell.
Most people will use toSql and fromSql instead of manipulating
The default representation of time values is an integer number of seconds.
Databases such as PostgreSQL with builtin timestamp types can will see
automatic conversion between these Haskell types to local types. Other
databases can just use an int or a string.
This behavior also exists for other types. For instance, many databases don't
have a Rational type, so they'll just use Haskell's show function and
store a Rational as a string.
Two SqlValues are considered to be equal if one of these hold (first one that
is true holds; if none are true, they are not equal):
* Both are NULL
* Both represent the same type and the encapsulated values are equal
* The values of each, when converted to a string, are equal.