**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**

**INT:**

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.

**NUMERIC(P,D)**:

It’s just like a function where the first parameter** P **defines the** **number 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.

**Fl0AT(N)**:

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**.

**CHAR(N)**:

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”.**

**VARCHAR(N)**:

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.

**DOUBLE PRECISION**:

All the Floating numbers are included here with machine-dependent Precision.

**SMALLINT**:

a subset of the integer domain type that is machine-dependent

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