What is the difference between DATETIME and TIMESTAMP?

DATETIME stores the literal value you give it, independent of time zone, with a wide range up to year 9999. TIMESTAMP is converted to UTC on write and back to the session time zone on read, but only spans 1970 to 2038.

Should I use VARCHAR or TEXT?

Use VARCHAR for short, bounded strings that you may want to index fully; it is stored inline in the row. Use TEXT for long content — it can be stored off-page and has length limits up to 4 GB for LONGTEXT, but indexes need a prefix length.

Why use DECIMAL for money instead of FLOAT?

FLOAT and DOUBLE are binary floating point and cannot represent many decimal fractions exactly, causing rounding errors. DECIMAL(M,D) stores the exact value, so it is the correct choice for currency and other exact figures.

What does UNSIGNED do?

UNSIGNED removes the negative half of an integer type's range and doubles the positive maximum. For example INT UNSIGNED goes from 0 to about 4.29 billion instead of roughly negative to positive 2.1 billion.

What happens to out-of-range values?

In the default STRICT SQL mode, inserting an out-of-range or wrongly typed value raises an error and the statement fails. Without strict mode, MySQL would silently clamp or truncate the value and emit a warning.

MySQL Data Types Reference

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Choose the right MySQL column type

MySQL and MariaDB provide integer, fixed and floating-point, string, binary, date/time and JSON types, each with its own storage cost and range. This reference lets you search those types by name or range and filter by category, so you can size each column correctly. It runs entirely in your browser.

How it works

Each entry shows the type, its category, the on-disk storage size and the value range, plus a note for types whose behaviour depends on time zone or SQL mode. Integer types come in five widths from TINYINT (1 byte) to BIGINT (8 bytes) and may be UNSIGNED. String and binary types split into inline CHAR/VARCHAR and off-page TEXT/BLOB families. A typical table uses several:

CREATE TABLE orders (
  id        BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  total     DECIMAL(12,2) NOT NULL,
  status    ENUM('new','paid','shipped') NOT NULL,
  created   DATETIME NOT NULL,
  payload   JSON
);

Tips and examples

Prefer the smallest integer type that fits expected values — narrower columns mean smaller indexes and faster scans.
VARCHAR(255) was historically common because of an index-prefix limit; with modern utf8mb4 and larger key lengths you can size it to the real maximum.
Add UNSIGNED to auto-increment primary keys to double the available id space.
When ordering by a TEXT/BLOB column you must specify a prefix length on the index, e.g. INDEX (body(100)).