How Can I Select Perticular Id From Table In If Else Condition

Instead of IF-ELSE you need to use CASE[^]
Here is a CodeProject article on the subject A Simple Use of SQL CASE Expression[^].

Member 10694442 said:

& i want to do this for all 4000 rows

Be aware that if you don't filter your SQL query using a WHERE[^] clause then it will affect every row on the table - more information here[^].

In your case this would work:

select CASE WHEN [close] > [ref] THEN 'Buy' ELSE 'Sell' END
from YourTable

Notice that I have surrounded the column names with square brackets because close is one of SQL Server's reserved words[^]. It is best practise to avoid using reserved words as column or variable names.