Oracle 11g Release 2

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create table TestReplace (Description varchar2(500),
                          ParamValue1 number,
                          ParamValue2 number,
                          ParamValue3 number);
INSERT ALL
  into TestReplace (Description) values ('This sentence has no parameteres, and it should be shown like this')
  into TestReplace (Description, ParamValue1) values ('This sentence has only one parametere, and it should be shown right here {param} with rest of text', 100)
  into TestReplace (Description, ParamValue1, ParamValue2) values ('This sentence has two parameteres, one here {param} and one here {param}, show full sentence', 100, 200)
  into TestReplace (Description, ParamValue1, ParamValue2, ParamValue3) values ('This sentence has all parameteres, here {param} and here {param} and there {param}', 100, 200, 300)
  SELECT * FROM DUAL;  
4 rows affected

SELECT * FROM TESTREPLACE;


DESCRIPTION
PARAMVALUE1
PARAMVALUE2
PARAMVALUE3


This sentence has no parameteres, and it should be shown like this
null
null
null

This sentence has only one parametere, and it should be shown right here {param} with rest of text
100
null
null

This sentence has two parameteres, one here {param} and one here {param}, show full sentence
100
200
null

This sentence has all parameteres, here {param} and here {param} and there {param}
100
200
300


SELECT REGEXP_REPLACE(REGEXP_REPLACE(REGEXP_REPLACE(DESCRIPTION,
                                                    '{param}', PARAMVALUE1, 1, 1),
                                     '{param}', PARAMVALUE2, 1, 1),
                      '{param}', PARAMVALUE3, 1, 1)
  FROM TESTREPLACE


REGEXP_REPLACE(REGEXP_REPLACE(REGEXP_REPLACE(DESCRIPTION,'{PARAM}',PARAMVALUE1,1,1),'{PARAM}',PARAMVALUE2,1,1),'{PARAM}',PARAMVALUE3,1,1)


This sentence has no parameteres, and it should be shown like this

This sentence has only one parametere, and it should be shown right here 100 with rest of text

This sentence has two parameteres, one here 100 and one here 200, show full sentence

This sentence has all parameteres, here 100 and here 200 and there 300

DESCRIPTION	PARAMVALUE1	PARAMVALUE2	PARAMVALUE3
This sentence has no parameteres, and it should be shown like this	null	null	null
This sentence has only one parametere, and it should be shown right here {param} with rest of text	100	null	null
This sentence has two parameteres, one here {param} and one here {param}, show full sentence	100	200	null
This sentence has all parameteres, here {param} and here {param} and there {param}	100	200	300