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Beginner Topic 17 of 51 Databases

Data Types in SQL

Column types like INT, VARCHAR and DATE.

How it works

SQL columns have types that define the allowed values, storage and operations. Common ones are INTEGER and BIGINT, DECIMAL or NUMERIC for exact numbers, FLOAT and DOUBLE for approximate ones, CHAR and VARCHAR and TEXT for strings, DATE, TIME and TIMESTAMP, BOOLEAN, BLOB for binary data, and JSON and UUID in many systems. Choosing the smallest suitable type saves space and speeds comparisons and indexes.

Step-by-step walkthrough

  1. INT stores whole numbers.
  2. DECIMAL stores exact numbers, perfect for money.
  3. VARCHAR stores variable length text.
  4. DATE and TIMESTAMP store times.
  5. Choosing the right type saves space and prevents invalid data.

Where it is used

Storing money as DECIMAL, dates as DATE or TIMESTAMP WITH TIME ZONE and flags as BOOLEAN gives correct sorting, arithmetic and validation.

Common pitfall

Using FLOAT for currency produces rounding errors. Storing numbers or dates as strings breaks sorting and comparisons. VARCHAR lengths and character sets matter for Unicode. Time zone handling is a frequent source of bugs, so store UTC. Implicit conversions can stop indexes from being used, so compare like with like.

Where it fits in the course

Data Types in SQL is topic 17 of 51 in Databases, rated Beginner. It follows Entity-Relationship Modeling. The next topic is Subqueries.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Databases quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Data Types in SQL?
Column types like INT, VARCHAR and DATE. It belongs to Databases and is a beginner-level topic.
Where do people use Data Types in SQL?
Storing money as DECIMAL, dates as DATE or TIMESTAMP WITH TIME ZONE and flags as BOOLEAN gives correct sorting, arithmetic and validation.
What is the most common mistake with Data Types in SQL?
Using FLOAT for currency produces rounding errors.
What should I learn before this topic?
Start with Entity-Relationship Modeling, the topic just before it in Databases.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Databases quiz.
Is Data Types in SQL hard to learn?
It is a Beginner topic, so it works as an entry point. If the terms are new, read the explanation twice and try the visualizer before the quiz.
How long does it take to learn Data Types in SQL?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Data Types in SQL?
Entity-Relationship Modeling, Subqueries, Inner and Outer Joins are closely connected. The full list is in the related topics section of this page.
What should I study after Data Types in SQL?
Continue with Subqueries, the next topic in Databases.

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