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MySQL/Data Types

Read a Table's Data Types

Practical lesson

Let's read exactly what DESCRIBE students; is telling us, column by column.

The id column has type int a whole number, and its Key is PRI, meaning it's the primary key, the column MySQL uses to uniquely identify each row (you'll cover primary keys properly soon).

The name column has type varchar(100) text, capped at 100 characters, and its Null is NO, meaning every row must have a name; it cannot be left empty.

The age column has type int, and its Null is YES, meaning it's allowed to be empty for a given row perhaps because a student's age wasn't recorded yet.

Notice how much this single command tells you without opening a single row of actual data: what each column stores, whether it's required, and which one uniquely identifies each record. Reading a table's structure this way, before you touch its data, is a habit worth building early.

Try it yourself
Code

Starter example

Code
DESCRIBE students;
Live preview
+-------+--------------+------+-----+---------+
| Field | Type         | Null | Key | Default |
+-------+--------------+------+-----+---------+
| id    | int          | NO   | PRI | NULL    |
| name  | varchar(100) | NO   |     | NULL    |
| age   | int          | YES  |     | NULL    |
+-------+--------------+------+-----+---------+
3 rows in set