SQL Data Types Explained: Text, Numbers, Dates, and Better Questions

A table tells you where data lives. Data types tell you what the values mean. That distinction sounds small, but it is one of the reasons SQL can do more than display rows on a screen.

In SQL for Files, you can practice this idea without setting up a database server. Load sample lesson data or bring your own CSV, JSON, or Parquet file into the browser, inspect the inferred columns, and run SQL locally with DuckDB WASM.

Most beginner SQL examples start with three everyday categories: text, numbers, and dates. They look obvious in a small table, but SQL treats them differently because they support different kinds of questions.

• Text stores words and characters, such as employee names, departments, product codes, or regions.
• Numbers store quantities and measures, such as salaries, prices, counts, and percentages.
• Dates store calendar or time values, such as hire dates, order dates, timestamps, and event times.

id          INTEGER
name        VARCHAR
department  VARCHAR
salary      DECIMAL
hire_date   DATE

A salary is not just characters on a screen. Because SQL understands it as a number, you can calculate a minimum, maximum, average, or total. A hire date is not just a label. Because SQL understands it as a date, you can sort chronologically or filter people hired after a certain day.

SELECT
  AVG(salary) AS average_salary,
  MIN(hire_date) AS earliest_hire_date
FROM employees;

Text has its own strengths. You can search for names, group by departments, match patterns, and label results. The important part is not that one type is better than another. The important part is that SQL chooses behavior based on type.

A common beginner surprise is that a value can look right but behave wrong. The value 2026 might be a number, part of a date, or text inside an ID. SQL needs the type to know whether it should add it, sort it alphabetically, compare it as a date, or preserve it exactly as written.

The second Learn SQL lesson introduces data types using a simple employee table. It shows why names, departments, salaries, and hire dates are not interchangeable, even when they all sit side by side in one row.

1. Open the related Data Types lesson below.
2. Notice which columns are text, numbers, and dates.
3. Then continue toward SELECT queries, where those types start to affect real results.