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SQL has several main **data types**, used to store information in tables. They can be grouped as follows:

### 1. Numeric types

- `INT` / `INTEGER`, integers, e.g. 10, 200
- `SMALLINT`, small integers
- `BIGINT`, large integers
- `DECIMAL(p, s)` / `NUMERIC(p, s)`, exact fixed-point numbers (p is the total number of digits, s is the number of digits after the decimal point), e.g. 123.45
- `FLOAT` / `REAL` / `DOUBLE`, floating-point numbers, suited to approximate calculations

### 2. Character types

- `CHAR(n)`, a fixed-length string of n characters, e.g. `CHAR(10)`
- `VARCHAR(n)`, a variable-length string up to n characters
- `TEXT`, large text data

### 3. Date & Time

- `DATE`, a date in YYYY-MM-DD format
- `TIME`, a time, e.g. HH:MM:SS
- `DATETIME` / `TIMESTAMP`, a date and time together
- `YEAR`, a year

### 4. The boolean type

- `BOOLEAN`, takes the values `TRUE` / `FALSE`

### 5. Other types

- `BLOB`, binary data (files, images)
- `JSON`, storing data in JSON format (supported by some DBMSs, e.g. MySQL, PostgreSQL)

Put simply, **a data type determines which values can be stored in a field**, and affects both the memory it uses and the operations that can be performed on that data.

If you'd like, I can put together **a table of every data type with examples**, to make it easier for a trainee to understand and remember. Should I?

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