There are several Oracle functions that allow you to convert to a preset data type (TO_DATE, TO_CHAR, TO_NUMBER).
There's also a function that allows you to specify the data type. This is the CAST function.
If, for some reason, you need to convert to a specific data type (and length or precision), you can use CAST. For example:
SELECT CAST(salary_request AS NUMBER(8)) FROM employee_feedback;
This will convert the salary_request column into a NUMBER(8) column.
You can do this with many different data types, so it's a very useful function.
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