| Oracle9i SQL Reference Release 2 (9.2) Part Number A96540-02  | 
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trunc_number::=
 The TRUNC (number) function returns n truncated to m decimal places. If m is omitted, then n is truncated to 0 places. m can be negative to truncate (make zero) m digits left of the decimal point.
The following example truncate numbers:
SELECT TRUNC(15.79,1) "Truncate" FROM DUAL; Truncate ---------- 15.7
SELECT TRUNC(15.79,-1) "Truncate" FROM DUAL; Truncate ---------- 10