Basic Data Types of SQL

As previously mentioned, each column in a table has a data type. We review the major data types here.

Numeric

Numeric data types are data types that represent numbers. The following figure provides an overview of some of the major types:

Figure 1.33: Major numeric data types

Character

Character data types store text information. The following figure summarizes character data types:

Figure 1.34: Major character data types

Under the hood, all of the character data types use the same underlying data structure in PostgreSQL and many other SQL databases, and most modern developers do not use char(n).

Boolean

Booleans are a data type used to represent True or False. The following table summarizes values that are represented as Boolean when used in a query with a data column type of Boolean:

Figure 1.35: Accepted Boolean values

While all of these values are accepted, the values of True and False are considered to be compliant with best practice. Booleans can also take on NULL values.

Datetime

The datetime data type is used to store time-based information such as dates and times. The following are some examples of datetime data types:

Figure 1.36: Popular datetime data types

We will discuss this data type more in Chapter 5, Analytics Using Complex Data Types.

Data Structures: JSON and Arrays

Many versions of modern SQL also support data structures such as JavaScript Object Notation (JSON) and arrays. Arrays are simply lists of data usually written as members enclosed in square brackets. For example, ['cat', 'dog', 'horse'] is an array. A JSON object is a series of key-value pairs that are separated by commas and enclosed in curly braces. For example, {'name': 'Bob', 'age': 27, 'city': 'New York'} is a valid JSON object. These data structures show up consistently in technology applications and being able to use them in a database makes it easier to do many kinds of analysis work.

We will discuss data structures in more detail in Chapter 5, Analytics Using Complex Data Types.

We will now look at the basic operations in an RDBMS using SQL.