Choosing the Right Date/Time Storage in MySQL and PostgreSQL

Storing time information is a fundamental requirement in software development. The choice of MySQL date‑time types directly affects data accuracy, storage efficiency, query performance, and system stability.

Avoid storing dates as strings. Using VARCHAR for dates wastes space, makes comparisons inefficient, limits the use of built‑in date functions, and results in poor index performance.

DATETIME vs TIMESTAMP. DATETIME stores the literal date‑time value without any time‑zone information. TIMESTAMP converts the input to UTC on write and converts back to the session time‑zone on read, making it suitable for multi‑time‑zone applications.

CREATE TABLE `time_zone_test` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `date_time` datetime NULL,
  `time_stamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Inserting a row with the session time‑zone set to UTC+0:

INSERT INTO time_zone_test(date_time,time_stamp) VALUES(NOW(), NOW());

Querying the data in the same session returns identical values for both columns. After changing the session time‑zone to UTC+8:

SET time_zone = '+8:00';

the time_stamp column is automatically displayed in the new zone, while date_time remains unchanged.

PostgreSQL equivalents. PostgreSQL does not have a DATETIME type. TIMESTAMP WITHOUT TIME ZONE behaves like MySQL DATETIME , and TIMESTAMP WITH TIME ZONE (or TIMESTAMPTZ ) corresponds to MySQL TIMESTAMP , handling UTC conversion automatically.

Comparison summary. Roughly:

DATETIME: 5‑8 bytes, no time‑zone, range 1000‑01‑01 ~ 9999‑12‑31.

TIMESTAMP: 4‑7 bytes, includes time‑zone, range 1970‑01‑01 ~ 2038‑01‑19.

Numeric Unix timestamp: 4 bytes, no time‑zone, range from 1970‑01‑01 onward.

Selection recommendations.

Use TIMESTAMP when the application needs automatic time‑zone handling and the 2038 limitation is acceptable.

Choose DATETIME for scenarios without time‑zone conversion or when dates beyond 2038 are required.

Consider a numeric Unix timestamp for maximum comparison performance and cross‑system compatibility, accepting reduced readability.

There is no one‑size‑fits‑all solution; developers should pick the type that best matches their specific business requirements.