accessing record from table and storing it as variable

My table consists of fields like this

S.N. ------Customer_ID---------- Loan_taken_on(Date) ----------Payment_made_in(date)

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1 -------- 5001 ----------------------- 2013/05/12----------------------NULL------------------------

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Now as the user tries to update the table

• The "loan_taken_on" has to get retrieved and stored in a variable (suppose @entry_date)