Ben Becker created DRILL-262:
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Summary: Implement support for DATETIME and TIMESTAMP types
Key: DRILL-262
URL: https://issues.apache.org/jira/browse/DRILL-262
Project: Apache Drill
Issue Type: Task
Reporter: Ben Becker
Many functions and operators in Drill need to handle DATETIME and TIMESTAMP
types. This may require two formats; the most important of which is an
expanded format for use during processing:
{code}
struct pg_tm
{
int tm_sec;
int tm_min;
int tm_hour;
int tm_mday;
int tm_mon; /* origin 0, not 1 */
int tm_year; /* relative to 1900 */
int tm_wday;
int tm_yday;
int tm_isdst;
long int tm_gmtoff;
const char *tm_zone;
};
{code}
Note that:
- Fractions of seconds are stored in an auxiliary 32-bit integer (thus internal
time functions usually take both pg_tm and fsec_t arguments).
- Resolution is guaranteed to the microsecond, with a date range of 4713 BC -
294276 AD.
- MySQL stores datetime values as simple unix time format (second resolution,
1970 - 2038 date range)
In Postgres, the TIMESTAMP type is encoded into 64 bits for storage as follows:
- The date portion is packed in the upper 28 bits as the delta of years, months
and days since postgres epoch (1/1/2000).
- The time portion is packed in the lower 36 bits as hours, minutes, seconds
and fsecs (fractions of a second).
- The specific encoding logic can be found in
{{src/backend/utils/adt/timestamp.c}} in {{tm2timestamp()}}, {{date2j()}} and
{{time2t()}}.
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