How to Declare Data Types in MariaDB

How do I choose the right data type in MariaDB?

Assigning the correct data type to a column so MariaDB stores values efficiently, accurately, and with optimal performance.

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Description

What are MariaDB data types used for?

Data types tell MariaDB how much space to reserve, which operations are allowed, and how to validate inserted values. Choosing correctly prevents over-allocating storage and avoids runtime casting errors.

Which integer type fits common IDs?

Use INT for up to ~2.1 billion signed values; switch to BIGINT for larger ranges.Add UNSIGNED when negative numbers are impossible, doubling the positive range without extra space.

How to store money amounts safely?

Prefer DECIMAL(p,s) for fixed-precision currency (e.g., DECIMAL(10,2) for prices up to 99 999 999.99). Avoid FLOAT/DOUBLE because binary fractions can cause rounding errors.

When should I pick VARCHAR vs. TEXT?

Choose VARCHAR(n) for variable-length strings ≤65 535 bytes; MariaDB stores only actual length, saving space.Use TEXT for longer blobs of text that rarely participate in indexed searches.

How are dates and times represented?

Use DATE for calendar dates, DATETIME for combined date & time, and TIMESTAMP when you need automatic UTC conversion or default current time.

Can I alter an existing column’s type safely?

Yes. Run ALTER TABLE table_name MODIFY column_name NEW_TYPE [...options]; in a maintenance window.Always back up first, and ensure the new type is compatible to avoid data truncation.

Best practices for ecommerce schemas?

• Use BIGINT UNSIGNED for Order IDs if you expect millions of rows.
• Store product prices as DECIMAL(10,2).
• Track stock in INT UNSIGNED.
• Record order dates with DATETIME.

How to confirm your choices?

Query INFORMATION_SCHEMA.COLUMNS to review types and sizes, then run representative inserts & aggregations to benchmark performance.

Why How to Declare Data Types in MariaDB is important

How to Declare Data Types in MariaDB Example Usage


-- Review data types chosen for critical ecommerce tables
SELECT table_name, column_name, column_type
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  table_schema = 'shop_db'
  AND  table_name IN ('Customers','Orders','Products','OrderItems');

How to Declare Data Types in MariaDB Syntax


-- Creating a table with data types
CREATE TABLE Products (
    id            BIGINT UNSIGNED PRIMARY KEY,
    name          VARCHAR(255)        NOT NULL,
    price         DECIMAL(10,2)       NOT NULL,
    stock         INT UNSIGNED        DEFAULT 0,
    created_at    DATETIME            DEFAULT CURRENT_TIMESTAMP
);

-- Altering a column's data type safely
ALTER TABLE Orders
MODIFY total_amount DECIMAL(12,2) NOT NULL;

Common Mistakes

Using FLOAT for currency: FLOAT introduces binary rounding errors that break financial totals. Fix by switching to DECIMAL with enough precision, e.g., DECIMAL(10,2).
Leaving text columns as LONGTEXT by default: Oversized types waste space and slow indexes. Define VARCHAR with realistic length limits instead.

Frequently Asked Questions (FAQs)

Can I change a column from INT to BIGINT later?

Yes, but expect table locking. Schedule downtime or use online DDL in MariaDB Enterprise.

Does VARCHAR(255) always allocate 255 bytes?

No. MariaDB stores only the actual length plus 1–2 bytes for length metadata.

When should I use ENUM?

Use ENUM for short, fixed lists such as order status ('pending','shipped','delivered'). It stores values compactly as integers but remains human-readable.