Unapply Credit Memo

In the below update statement if the PREVIOUS_CUSTOMER_TRX_ID is given as ''  it will unapply the application

update RA_CUSTOMER_TRX_ALL set
PREVIOUS_CUSTOMER_TRX_ID = ''
where CUSTOMER_TRX_ID = XCMIDX;

update RA_CUSTOMER_TRX_LINES_ALL set
PREVIOUS_CUSTOMER_TRX_ID = ''
where CUSTOMER_TRX_ID = XCMIDX;

update RA_CUSTOMER_TRX_LINES_ALL set
PREVIOUS_CUSTOMER_TRX_LINE_ID = ''
where CUSTOMER_TRX_ID = XCMIDX;