PostgresQL date and time
Published: 2023-04-24 14:28:11

##PostgreSQL's Date and Time Data Types
PostgreSQL provides several built-in data types for representing date and time values, including date, time, timestamp, interval, timetz, and timestamptz. These data types allow you to store and manipulate various aspects of date and time information, such as year, month, day, hour, minute, second, and time zone. Let's take a closer look at how PostgreSQL handles these data types internally.

##Date and Time Storage
PostgreSQL uses a fixed-length storage format for date and time values. The date data type occupies 4 bytes of storage and represents a date without a time or time zone component. The time data type also takes up 4 bytes of storage and represents a time of day without a date or time zone component. The timestamp data type requires 8 bytes of storage and represents a date and time with optional fractional seconds. The interval data type, used to represent time intervals, requires 16 bytes of storage.

PostgreSQL uses a combination of Julian day numbers and time since midnight to represent dates and times internally. Julian day numbers are integer values that represent the number of days since November 24, 4714 BC, according to the Gregorian calendar. Time since midnight is represented as the number of microseconds (or fractions thereof) elapsed since midnight.

##Time Zone Handling
Handling time zones can be complex, but PostgreSQL provides two data types to deal with time zone information: timetz and timestamptz. The timetz data type represents a time of day with a time zone offset, while the timestamptz data type represents a timestamp with a time zone offset. Both timetz and timestamptz store the date, time, and time zone offset information.

PostgreSQL internally stores all timetz and timestamptz values in Coordinated Universal Time (UTC). When a value is entered or retrieved, PostgreSQL automatically converts it to the specified time zone based on the time zone offset information stored in the data type. This ensures that date and time values are stored and retrieved accurately, regardless of the time zone in which the database server is located or the client application is running.

##Date and Time Functions
PostgreSQL provides a rich set of functions for manipulating date and time values, allowing you to perform various operations, such as arithmetic, comparison, formatting, and extraction, on date and time data. These functions are implemented using the internal storage format and handling mechanisms described above, ensuring accurate and efficient manipulation of date and time values.

For example, the date_trunc function allows you to truncate a date or timestamp value to a specified precision, such as year, month, day, hour, minute, or second. This function uses the Julian day number and time since midnight representation to perform the truncation operation accurately.

Another example is the interval data type, which allows you to represent and perform arithmetic operations on time intervals. The interval data type internally stores the interval as the number of months, days, hours, minutes, and seconds, allowing you to perform arithmetic operations, such as addition and subtraction,