atof returns its argument as a single precision floating point. If the string cannot be parsed and converted to a valid float, a value 0.0 is returned.
Single precision floating point
SQL> select atof('1.23456789');
callret
REAL
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1.234568
1 Rows. -- 5 msec.
SQL> select atof ('Cadena de los patos amarillos');
callret
REAL
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0.000000
1 Rows. -- 4 msec.
SQL> select atof (sprintf ('%f', 2.3423));
callret
REAL
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2.342300
1 Rows. -- 5 msec.