A user-defined data types in SQL are Domain Type. You can use the domain instead of a built-in SQL data type. To know the difference between user-defined and built-in data types check our post. You can use the domain instead of a built-in SQL data type when declaring a column. That column will then be restricted only to use the same domain. Some good definitions of Domain type in SQL are found HERE.
Domain Types in SQL
Representing Numbers in SQL table.
There are Finite integers and it varies from machine to machine. The Size will contain in the database is also machine-dependent.
It’s just like a function where the first parameter P defines thenumber left to the decimal point and the second Parameter D defines the number right to the decimal point. Let’s say we have defined a table column with storing NUMERIC(2,2). We gave the number 24.65 to store It will store it correctly, But if we provide a number 233.4 or 2.343 then It will not be stored correctly.
It is just like numeric but here the parameter is only the precision to the right. For Example, if the FLOAT(2) is defined for a column and we store a 2.42 it will be stored correctly but it will not store 3.433.
User-specified length n for a fixed-length character string. For example, we defined CHAR(3) to store values in a column, The value “AHE” will be stored correctly but it will not store “AH” or “AHEE”.
It is the same as the CHAR(N) with N only defining the maximum length, not the fixed length. For example, if we define VARCHAR(3) we can store strings up to the length of 3 like “AAA”, “A”, “AA”, etc but can’t store “AAAA” because it will exceed the maximum length.
All the Floating numbers are included here with machine-dependent Precision.
a subset of the integer domain type that is machine-dependent