SQL> drop table sam_800
  2  /
drop table sam_800
           *
ERROR at line 1:
ORA-00942: table or view does not exist


Elapsed: 00:00:00.36
SQL> create table sam_800(a number(5,2)) tablespace warehouse_small_data;

Table created.

Elapsed: 00:00:00.18
SQL> insert into sam_800 values(100.00);

1 row created.

Elapsed: 00:00:00.18
SQL> insert into sam_800 values(-100.00);

1 row created.

Elapsed: 00:00:00.18
SQL> insert into sam_800 values(-100.585);

1 row created.

Elapsed: 00:00:00.18
SQL> select * from sam_800;

         A
----------
       100
      -100
   -100.59

Elapsed: 00:00:00.36

orclz> select case sign(a) when -1 then -1*a else a end from sam_800;

CASESIGN(A)WHEN-1THEN-1*AELSEAEND
---------------------------------
                              100
                              100
                           100.59

orclz> select sqrt(a*a) from sam_800;

 SQRT(A*A)
----------
       100
       100
    100.59

orclz>

SQL> WITH test AS (SELECT 100 col FROM DUAL
  2                UNION
  3                SELECT -200 FROM DUAL
  4                UNION
  5                SELECT -0.343 FROM DUAL)
  6  SELECT col,
  7         DECODE (SUBSTR (TO_CHAR (col), 1, 1),
  8                 '-', to_number(SUBSTR (TO_CHAR (col), 2)),
  9                 col)
 10            result
 11    FROM test;

       COL     RESULT
---------- ----------
      -200        200
     -,343       ,343
       100        100

SQL>

orclz> select case when a+a > a then a else -1*a end from sam_800;

CASEWHENA+A>ATHENAELSE-1*AEND
-----------------------------
                          100
                          100
                       100.59

orclz>

SQL> with tbl as 
       (select 100 a from dual 
        union all 
        select -100 from dual
        union all
        select 0.5 from dual
        union all
        select -0.5 from dual)
      select a, case when exp(a)<1 then -1*a else a end from tbl;

         A CASEWHENEXP(A)<1THEN-1*AELSEAEND
---------- --------------------------------
       100                              100
      -100                              100
        .5                               .5
       -.5                               .5

SQL>

orclz> select a,to_number(replace(to_char(a),'-')) from sam_800;

         A TO_NUMBER(REPLACE(TO_CHAR(A),'-'))
---------- ----------------------------------
       100                                100
      -100                                100
   -100.59                             100.59

orclz>

SQL> with tbl as
  2         (select 100 a from dual
  3          union all
  4          select -100 from dual
  5          union all
  6          select 0.5 from dual
  7          union all
  8          select -0.5 from dual)
  9  SELECT LTRIM(a,'-') FROM tbl;
 
LTRIM(A,'-')
----------------------------------------
100
100
.5
.5