The TRUNC function accepts two numeric value expressions (n,m) as
    arguments. The result is the first value expression n truncated
    to m places to the right of the decimal point. The value
    expression m can be negative to truncate digits to the left of
    the decimal point. The data type of m must be an unscaled numeric
    value (tinyint, smallint, integer, or bigint). If omitted, m
    defaults to zero. See the following example.

    SQL> select avg (salary_amount)
    cont> from salary_history
    cont> where employee_id = '00164';

      3.857350000000000E+004
    1 row selected

    SQL> select trunc (avg (salary_amount)) as SAL edit using 'sz(9).99'
    cont> from salary_history
    cont> where employee_id = '00164';
               SAL
          38574.00
    1 row selected

    Usage Notes

    o  The function TRUNC for numeric values is supported as a native
       function in Oracle Rdb.

    o  Fixed point values are truncated and rounded correctly.
       Floating values, while supported by TRUNC, may not always
       return the expected results. Please review usage of TRUNC in
       such contexts.

    o  The result type for TRUNC will match the data type of the
       input source parameter.

    o  The implementation of TRUNC for DATE values requires the use
       of the OCI Services for Rdb library (also know as SQL*net for
       Rdb). These functions will now accept DATE ANSI, TIMESTAMP and
       DATE VMS values.

    o  Attempts to use TRUNC on a database that is not setup for OCI
       Services will receive errors similar to these:

       SQL> select TRUNC (current_date) from rdb$database;
       %RDB-E-OBSOLETE_METADA, request references metadata objects that no longer exist
       -RDMS-F-BAD_SYM, unknown routine symbol - TRUN2
       SQL> select ROUND (current_date) from rdb$database;
       %RDB-E-OBSOLETE_METADA, request references metadata objects that no longer exist
       -RDMS-F-BAD_SYM, unknown routine symbol - ROUN2

                                      NOTE

          The special functions ROUN2 and TRUN2 are internal
          routines to deal with DATE types.

    o  TRUNC supports the data types REAL, FLOAT and DOUBLE PRECISION
       for both parameter and results. However, due to the imprecise
       nature of floating point arithmetic this may cause unexpected
       results. A value such as 4.185 will not round to 4.19 as
       expected because the internal (and approximate) representation
       of the number is something like 4.184999942780E+000 and
       therefore does not appear to require rounding to the second
       decimal place according to the rounding rules.

       The following example shows this problem.

       SQL> select cast(round (4.185,2) as integer(2)) from rdb$database;

                 4.18
       1 row selected
       SQL> select cast(round (4.175,2) as integer(2)) from rdb$database;

                 4.18
       1 row selected
       SQL>

                                      NOTE

          The result of a divide operation (/) or the AVG, STDDEV,
          VARIANCE statistical functions are floating point values,
          so applying TRUNC or ROUND to those results, even if
          performed on integer sources, will also be affected by
          the intermediate floating point type.

    o  If you use SQL to access older versions of Rdb (such as via
       remote access) then SQL will revert to the previous behavior
       and use the SQL functions provided by the SQL_FUNCTIONS
       library.