SELECT ... WHERE column LIKE parameter||'%'

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I have a database containing alot of procedures with this kind of coding logic:


BigTable
column1 varchar2(40);


Procedure SomeProcedure (in_parameter varchar2)
SELECT column1
FROM BigTable
WHERE column1 LIKE in_parameter||' %';
END;


The procedure is called like this:

SomeProcedure(' abc');


Although this coding logic selects the correct rows, there is a big problem - it does not use the index on BigTable.
But if you do perform at little test and change the procedure like this:


Procedure SomeProcedure (in_parameter varchar2)
SELECT column1
FROM BigTable
WHERE column1 LIKE 'abc'||'%';
END;

Then it uses the index. But ofcourse now there is not the desired flexibility of using a parameter.


QUESTIONS:
1. Why does Oracle not use the index when a parameter is used in the LIKE-statement?