Practical SQL

3UNDERSTANDING DATA TYPES

Whenever I dig into a new database, I check the data type specified for each column in each table. If I’m lucky, I can get my hands on a data dictionary: a document that lists each column; specifies whether it’s a number, character, or other type; and explains the column values. Unfortunately, many organizations don’t create and maintain good documentation, so it’s not unusual to hear, “We don’t have a data dictionary.” In that case, I try to learn by inspecting the table structures in pgAdmin.

It’s important to understand data types because storing data in the appropriate format is fundamental to building usable databases ...