8.4 Date and Time Functions

8.4.1 DATEADD()

Available inDSQL, PSQL

Result typeDATE, TIME or TIMESTAMP

Syntax

1. DATEADD (<args>)

3. <args> ::=
4. <amount> <unit> TO <datetime>
5. | <unit>, <amount>, <datetime>

7. <amount> ::= an integer expression (negative to subtract)
8. <unit> ::=
9. YEAR | MONTH | WEEK | DAY
10. | HOUR | MINUTE | SECOND | MILLISECOND
11. <datetime> ::= a DATE, TIME or TIMESTAMP expression

Table 8.4.1.1 DATEADD Function Parameters

Adds the specified number of years, months, weeks, days, hours, minutes, seconds or milliseconds to a date/time value.

• The result type is determined by the third argument.
• With TIMESTAMP and DATE arguments, all units can be used.
• With TIME arguments, only HOUR, MINUTE, SECOND and MILLISECOND can be used.

8.4.1.1 Examples of DATEADD

1. dateadd (28 day to current_date)
2. dateadd (-6 hour to current_time)
3. dateadd (month, 9, DateOfConception)
4. dateadd (-38 week to DateOfBirth)
5. dateadd (minute, 90, cast('now' as time))
6. dateadd (? year to date '11-Sep-1973')

1. select
2. cast(dateadd(-1 * extract(millisecond from ts) millisecond to ts) as varchar(30)) as t,
3. extract(millisecond from ts) as ms
4. from (
5. select timestamp '2014-06-09 13:50:17.4971' as ts
6. from rdb$database
7. ) a

1. T                        MS
2. ------------------------ ------
3. 2014-06-09 13:50:17.0000  497.1

See alsoSection 8.4.2, DATEDIFF(), Operations Using Date and Time Values

8.4.2 DATEDIFF()

Available inDSQL, PSQL

Result typeBIGINT

Syntax

1. DATEDIFF (<args>)

3. <args> ::=
4. <unit> FROM <moment1> TO <moment2>
5. | <unit>, <moment1>, <moment2>

7. <unit> ::=
8. YEAR | MONTH | WEEK | DAY
9. | HOUR | MINUTE | SECOND | MILLISECOND
10. <momentN> ::= a DATE, TIME or TIMESTAMP expression

Table 8.4.2.1 DATEDIFF Function Parameters

Returns the number of years, months, weeks, days, hours, minutes, seconds or milliseconds elapsed between two date/time values. (The WEEK unit is new in 2.5.)

• DATE and TIMESTAMP arguments can be combined. No other mixes are allowed.
• With TIMESTAMP and DATE arguments, all units can be used. (Prior to Firebird 2.5, units smaller than DAY were disallowed for DATEs.)
• With TIME arguments, only HOUR, MINUTE, SECOND and MILLISECOND can be used.

Computation

• DATEDIFF doesn’t look at any smaller units than the one specified in the first argument. As a result,

• datediff (year, date '1-Jan-2009', date '31-Dec-2009') returns 0, but

• datediff (year, date '31-Dec-2009', date '1-Jan-2010') returns 1

• It does, however, look at all the bigger units. So:

• datediff (day, date '26-Jun-1908', date '11-Sep-1973') returns 23818

• A negative result value indicates that moment2 lies before moment1.

8.4.2.1 DATEDIFF Examples

1. datediff (hour from current_timestamp to timestamp '12-Jun-2059 06:00')
2. datediff (minute from time '0:00' to current_time)
3. datediff (month, current_date, date '1-1-1900')
4. datediff (day from current_date to cast(? as date))

See alsoSection 8.4.1, DATEADD(), Operations Using Date and Time Values

8.4.3 EXTRACT()

Available inDSQL, ESQL, PSQL

Result typeSMALLINT or NUMERIC

Syntax

1. EXTRACT (<part> FROM <datetime>)

3. <part> ::=
4. YEAR | MONTH | WEEK
5. | DAY | WEEKDAY | YEARDAY
6. | HOUR | MINUTE | SECOND | MILLISECOND
7. | TIMEZONE_HOUR | TIMEZONE_MINUTE
8. <datetime> ::= a DATE, TIME or TIMESTAMP expression

Table 8.4.3.1 EXTRACT Function Parameters

Extracts and returns an element from a DATE, TIME or TIMESTAMP expression.

8.4.3.1 Returned Data Types and Ranges

The returned data types and possible ranges are shown in the table below. If you try to extract a part that isn’t present in the date/time argument (e.g. SECOND from a DATE or YEAR from a TIME), an error occurs.

Table 8.4.3.1.1 Types and ranges of EXTRACT results

8.4.3.1.1 MILLISECOND

Firebird 2.1 and up support extraction of the millisecond from a TIME or TIMESTAMP. The data type returned is NUMERIC(9,1).

Note

If you extract the millisecond from Section 11.4, CURRENT_TIME, be aware that this variable defaults to seconds precision, so the result will always be 0. Extract from CURRENT_TIME(3) or Section 11.5, CURRENT_TIMESTAMP to get milliseconds precision.

8.4.3.1.2 WEEK

Firebird 2.1 and up support extraction of the ISO-8601 week number from a DATE or TIMESTAMP. ISO-8601 weeks start on a Monday and always have the full seven days. Week 1 is the first week that has a majority (at least 4) of its days in the new year. The first 1-3 days of the year may belong to the last week (52 or 53) of the previous year. Likewise, a year’s final 1-3 days may belong to week 1 of the following year.

Caution

Be careful when combining WEEK and YEAR results. For instance, 30 December 2008 lies in week 1 of 2009, so extract(week from date '30 Dec 2008') returns 1. However, extracting YEAR always gives the calendar year, which is 2008. In this case, WEEK and YEAR are at odds with each other. The same happens when the first days of January belong to the last week of the previous year.

Please also notice that WEEKDAY is not ISO-8601 compliant: it returns 0 for Sunday, whereas ISO-8601 specifies 7.

See alsoData Types for Dates and Times

8.4.4 FIRST_DAY()

Available inDSQL, PSQL

Result TypeDATE, TIMESTAMP (with or without time zone)

Syntax

1. FIRST_DAY(OF <period> FROM date_or_timestamp)

3. <period> ::= YEAR | MONTH | WEEK

Table 8.4.4.1 FIRST_DAY Function Parameters

FIRST_DAY returns a date or timestamp (same as the type of date_or_timestamp) with the first day of the year, month or week of a given date or timestamp value.

Note

• The first day of the week is considered as Sunday, following the same rules as for Section 8.4.3, EXTRACT() with WEEKDAY.
• When a timestamp is passed, the return value preserves the time part.

8.4.4.1 Examples of FIRST_DAY

1. select first_day(of month from current_date) from rdb$database;
2. select first_day(of year from current_timestamp) from rdb$database;
3. select first_day(of week from date '2017-11-01') from rdb$database;

8.4.5 LAST_DAY()

Available inDSQL, PSQL

Result TypeDATE, TIMESTAMP (with or without time zone)

Syntax

1. LAST_DAY(OF <period> FROM date_or_timestamp)

3. <period> ::= YEAR | MONTH | WEEK

Table 8.4.5.1 LAST_DAY Function Parameters

LAST_DAY returns a date or timestamp (same as the type of date_or_timestamp) with the last day of the year, month or week of a given date or timestamp value.

Note

• The last day of the week is considered as Saturday, following the same rules as for Section 8.4.3, EXTRACT() with WEEKDAY.
• When a timestamp is passed, the return value preserves the time part.

8.4.5.1 Examples of LAST_DAY

1. select last_day(of month from current_date) from rdb$database;
2. select last_day(of year from current_timestamp) from rdb$database;
3. select last_day(of week from date '2017-11-01') from rdb$database;