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Unix Timestamp in PostgreSQL
PostgreSQL can convert between timestamps and Unix-style epoch seconds using extract(epoch) and to_timestamp(). PostgreSQL also distinguishes timestamp values with and without timezone semantics, so the database type matters.
Working example
extract(epoch from ...) returns a numeric epoch value. to_timestamp() converts epoch seconds to a timestamp with timezone. Be explicit about timezone information at the application boundary so a plain local timestamp is not mistaken for an absolute instant.
Unit and timezone checks
In PostgreSQL, separate the database’s native timestamp types from the integer epoch representation used by external systems. This makes SQL-side date operations easier while keeping API conversions explicit.
- Confirm whether the API expects seconds or milliseconds.
- When interpreting a local calendar time in SQL, confirm its timezone before converting it to an epoch value; an offset mistake changes the represented instant.
- Keep UTC as the reference when comparing distributed logs.
- Do not infer the unit solely from digit count.
Common mistakes in PostgreSQL
- Passing milliseconds where an API expects seconds.
- Formatting a local time as if it were UTC.
- Dropping fractional seconds when the application requires millisecond precision.
- Using manual UTC offsets instead of the runtime's timezone-aware facilities.
When to use Unix timestamps
PostgreSQL is well suited to retaining timestamp types internally while exposing Unix numbers only where a protocol or downstream application requests them.
Related Timestamp Tools
Unix Timestamps in PostgreSQL: SQL at the Time Boundary
PostgreSQL can convert between timestamps and Unix seconds using EXTRACT(EPOCH FROM ...) and to_timestamp(...). This is useful when a database must exchange epoch values with an API while still using PostgreSQL's richer timestamp types internally.
Keep native timestamps internally when practical
A native PostgreSQL timestamp can be easier to query, compare, index, and format than a raw integer. At an API boundary, convert to Unix seconds when the external contract calls for it. For milliseconds, multiply the epoch seconds by 1,000 while preserving enough precision for the target system.
Example code
Quick reference
Practical checks
- Use TIMESTAMPTZ when timezone-aware instants are required.
- Document the unit of numeric API fields.
- Test both directions with a known UTC instant.
- Be careful when mixing timestamp values with local-time business rules.
Frequently Asked Questions: Practical Details
What does EXTRACT(EPOCH...) return?
It returns the number of seconds relative to the Unix Epoch for the supplied timestamp value.
How do I convert PostgreSQL epoch seconds back to a timestamp?
Use to_timestamp() with the numeric epoch value.
Should every database timestamp be stored as an integer?
No. PostgreSQL native timestamp types can be preferable for database-side date/time operations; use integers when an external protocol specifically needs them.
Frequently Asked Questions
How does PostgreSQL represent the current Unix time?
Use the extract(epoch) facilities shown on this page and confirm the returned unit in the language documentation.
How should PostgreSQL expose epoch precision to an API?
Choose the precision required by the API and document it explicitly. PostgreSQL can calculate epoch seconds while application code can scale the value when finer precision is required.
How should PostgreSQL handle timezone consistency?
For cross-service PostgreSQL comparisons, use a consistent UTC-oriented representation and keep local business time rules explicit.