Using If else in SQL Select statement

SELECT CASE WHEN IDParent < 1 
            THEN ID 
            ELSE IDParent 
       END AS colname 
FROM yourtable

Here, using CASE Statement and find result:

select (case when condition1 then result1
             when condition2 then result2
             else result3
             end) as columnname from tablenmae:

For example:

select (CASE WHEN IDParent< 1 then ID 
             else IDParent END) as columnname
from tablenmae

you can use CASE

SELECT   ...,
         CASE WHEN IDParent < 1 THEN ID ELSE IDPArent END AS ColumnName,
         ...
FROM     tableName