Date, Time and Datetime Fields

The eXtremeDB   datetime type is a 64-bit integer value used to store the date and time in databases. The precision of datetime values is determined by the runtime parameter DATETIME_PRECISION. Numerically, the precision represents the number of ticks per second. The default value for DATETIME_PRECISION is 1, which means that the database stores a datetime value as the number of seconds since the EPOCH (i.e. 00:00:00 UTC 1 January 1970). The resolution of datetime fields can be changed by an application at runtime to a resolution ranging from 1 (to store the number of seconds) to 1000000000 (for the number of nanoseconds). (However, note that the Java Date type uses millisecond resolution and the C# Datetime uses 100-nanosecond resolution. So these limitations apply to the database values possible with these native language APIs.)

It is important to note that the value of DATETIME_PRECISION is a per-process parameter; all processes working with the same database must set the same value for DATETIME_PRECISION. Respectively, all databases accessed from a given process will have the same precision.

Arithmetic on Date, Time and Datetime Fields

When using date, time or datetime fields in SQL, if any operand of the arithmetic expression is of type date, time or datetime, then the other operand is converted to datetime and the result of expression is of type datetime. The result will be formatted for output depending on the original type. So, for example a date field day could be incremented day+5 and the result will be of type date.

However, note that outside SQL, date and time fields are uint4 values, while datetime fields are uint8. There are no special "operations" defined for these fields. The above rule is applicable to SQL only.

Native Language APIs

The APIs for managing date, time and datetime fields are specific to the programming language used. Please use the links below to view detailed explanations and examples for your development environment:

SQL	Managing date, time and datetime fields in SQL
C	Managing date, time and datetime fields in C
C++	Managing date, time and datetime fields in C++
Java	Managing Date fields in Java
Python	Managing datetime fields in Python
C#	Managing Datetime fields in C#