8.4. Date and Time Functions

8.4.1. DATEADD()

Available inDSQL, PSQL

Changed in2.5

Syntax 

   |DATEADD (<args>)
   | 
   |<args> ::=
   |    <amount> <unit> TO <datetime>
   |  | <unit>, <amount>, <datetime>
   | 
   |<amount> ::= an integer expression (negative to subtract)
   |<unit> ::=
   |    YEAR | MONTH | WEEK | DAY
   |  | HOUR | MINUTE | SECOND | MILLISECOND
   |<datetime> ::= a DATE, TIME or TIMESTAMP expression

Table 8.45. DATEADD Function Parameters
ParameterDescription

amount

An integer expression of the SMALLINT, INTEGER or BIGINT type. A negative value is subtracted

unit

Date/time unit

datetime

An expression of the DATE, TIME or TIMESTAMP type

Result typeDATE, TIME or TIMESTAMP

DescriptionAdds the specified number of years, months, weeks, days, hours, minutes, seconds or milliseconds to a date/time value. (The WEEK unit is new in 2.5.)

  • The result type is determined by the third argument.

  • 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.

Examples 

  |dateadd (28 day to current_date)
  |dateadd (-6 hour to current_time)
  |dateadd (month, 9, DateOfConception)
  |dateadd (-38 week to DateOfBirth)
  |dateadd (minute, 90, time 'now')
  |dateadd (? year to date '11-Sep-1973')

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

8.4.2. DATEDIFF()

Available inDSQL, PSQL

Changed in2.5

Syntax 

   |DATEDIFF (<args>)
   | 
   |<args> ::=
   |    <unit> FROM <moment1> TO <moment2>
   |  | <unit>, <moment1>, <moment2>
   | 
   |<unit> ::=
   |    YEAR | MONTH | WEEK | DAY
   |  | HOUR | MINUTE | SECOND | MILLISECOND
   |<momentN> ::= a DATE, TIME or TIMESTAMP expression

Table 8.46. DATEDIFF Function Parameters
ParameterDescription

unit

Date/time unit

moment1

An expression of the DATE, TIME or TIMESTAMP type

moment2

An expression of the DATE, TIME or TIMESTAMP type

Result typeBIGINT

DescriptionReturns 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.

Examples 

  |datediff (hour from current_timestamp to timestamp '12-Jun-2059 06:00')
  |datediff (minute from time '0:00' to current_time)
  |datediff (month, current_date, date '1-1-1900')
  |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

Syntax 

  |EXTRACT (<part> FROM <datetime>)
  | 
  |<part> ::=
  |    YEAR | MONTH | WEEK
  |  | DAY | WEEKDAY | YEARDAY
  |  | HOUR | MINUTE | SECOND | MILLISECOND
  |<datetime> ::= a DATE, TIME or TIMESTAMP expression

Table 8.47. EXTRACT Function Parameters
ParameterDescription

part

Date/time unit

datetime

An expression of the DATE, TIME or TIMESTAMP type

Result typeSMALLINT or NUMERIC

DescriptionExtracts and returns an element from a DATE, TIME or TIMESTAMP expression. This function was already added in InterBase 6, but not documented in the Language Reference at the time.

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 8.48. Types and ranges of EXTRACT results
PartTypeRangeComment

YEAR

SMALLINT

1-9999

 

MONTH

SMALLINT

1-12

 

WEEK

SMALLINT

1-53

 

DAY

SMALLINT

1-31

 

WEEKDAY

SMALLINT

0-6

0 = Sunday

YEARDAY

SMALLINT

0-365

0 = January 1

HOUR

SMALLINT

0-23

 

MINUTE

SMALLINT

0-59

 

SECOND

NUMERIC(9,4)

0.0000-59.9999

includes millisecond as fraction

MILLISECOND

NUMERIC(9,1)

0.0-999.9

broken in 2.1, 2.1.1

8.4.3.2. MILLISECOND

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

ⓘ
Note

If you extract the millisecond from Section 9.4, “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 9.5, “CURRENT_TIMESTAMP” to get milliseconds precision.

8.4.3.3. WEEK

DescriptionFirebird 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