Time Queries
To make best use of Time Queries, it is a good idea to review the
time-related SQL data types, such as TIMESTAMP, DATE, TIME,
and INTERVAL.
These are covered in the SQL Data Types section.
It is also a good idea to review Endb's other time-related functions, in case they are helpful to you:
Note on SQL:2011 closed-open period model
All Endb temporal predicates (CONTAINS, OVERLAPS, PRECEDES,
SUCCEEDS, IMMEDIATELY PRECEDES, and IMMEDIATELY SUCCEEDS)
follow the SQL:2011 standard's "closed-open period model".
This means that a period represents all times starting from (and including)
the start time up to (but excluding) the end time.
Note on timezones
Endb currently only supports times encoded as UTC.
Now
Endb provides access to the current value of the clock "now" in multiple date/time configurations.
CURRENT_TIMESTAMP
CURRENT_TIMESTAMP gets the current date and time in UTC.
SELECT CURRENT_TIMESTAMP;
CURRENT_TIME
CURRENT_TIME gets the current time in UTC.
SELECT CURRENT_TIME;
CURRENT_DATE
CURRENT_DATE gets the current date in UTC.
Note that this may be different from your local date,
depending on the time of day when your query is run.
SELECT CURRENT_DATE;
System Time
All states an Endb database has ever seen are recorded, immutably.
Accessing these prior states is accomplished by querying System Time.
System Time is encoded in a special column, which is normally invisible to most queries,
named system_time (lower case).
Because system_time is invisible by default, it must be retrieved explicitly:
SELECTT *, system_time FROM products;
AS OF (Time Travel)
Endb permits time-traveling queries with the SQL:2011-compatible
AS OF operator.
The query will treat the DATE or TIMESTAMP supplied after AS OF
as if it were that time now.
SELECT * FROM products FOR SYSTEM_TIME AS OF 2023-08-25T00:00:00;
ALL (Time Omniscience)
Endb permits time-omniscient queries with the SQL:2011-compatible
ALL operator.
All states, across the entire history of the relevant tables, are
visible to a query suffixed with FOR SYSTEM_TIME ALL:
SELECT * FROM products FOR SYSTEM_TIME ALL;
BETWEEN
The syntax for time-aware BETWEEN is the same as the
normal BETWEEN operator.
Inspect System Time with the form FOR SYSTEM_TIME BETWEEN x AND y.
SELECT * FROM products FOR SYSTEM_TIME BETWEEN 2023-08-24T00:00:00 AND 2023-08-25T00:00:00;
FROM ... TO
Selects rows which fall between the two times, similar to BETWEEN,
but is exclusive of both the start and end times.
SELECT * FROM products FOR SYSTEM_TIME FROM 2023-08-24T00:00:00 TO 2023-08-30T00:00:00;
Period Predicates
The standard SQL:2011 period predicates are available.
CONTAINS
Returns TRUE if the second period is contained within the first.
SELECT {start: 2001-01-01, end: 2001-04-01} CONTAINS {start: 2001-02-01, end: 2001-04-01};
OVERLAPS
Returns TRUE if any part of the first period is found within the second.
SELECT {start: 2001-01-01, end: 2001-03-01} OVERLAPS {start: 2001-02-01, end: 2001-04-01};
PRECEDES
Returns TRUE if the first period ends before the second period begins.
SELECT 2001-03-01 PRECEDES [2001-04-01T00:00:00Z, 2001-05-01];
SUCCEEDS
Returns TRUE if the first period begins after the second period ends.
SELECT 2001-06-01 SUCCEEDS [2001-04-01T00:00:00Z, 2001-05-01];
IMMEDIATELY PRECEDES
Returns TRUE if the first period ends exactly as the second period begins.
SELECT 2001-04-01 IMMEDIATELY PRECEDES [2001-04-01T00:00:00Z, 2001-05-01];
IMMEDIATELY SUCCEEDS
Returns TRUE if the first period begins exactly as the second period ends.
SELECT 2001-05-01 IMMEDIATELY SUCCEEDS [2001-04-01T00:00:00Z, 2001-05-01];