In OpenERP first, install the sale and account module and then create the own module.

Follow these step given below:

Step1- Create your own module and then create merge_partner file and then pass this file in __init__.py file in your own module. Then create the function and pass this function in button.

Use this function given below:

import time
from lxml import etree
import decimal_precision as dp
from tools.translate import _
import netsvc
import pooler
from osv import fields, osv, orm
import datetime
from datetime import datetime
from datetime import date, timedelta
import types


class merge_partner(osv.osv):
    _name = 'merge.partner'    
    _columns ={
                'name1':fields.many2one('res.partner','Partner to Merge'),
                'name2':fields.many2one('res.partner','Partner on Merge'),              
                
            }

    def merge_on_partner(self, cr, uid, ids, context=None):
        res = {}
        for partners in self.browse(cr,uid,ids,context=None):
            print "===partners====",partners
            if partners:
                pid1 = partners.name1.id
                pid2 = partners.name2.id
                cr.execute('update sale_order set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update sale_order_line set order_partner_id = %s where order_partner_id = %s',(pid2,pid1))
                cr.execute('update account_invoice set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update account_invoice_line set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update account_move set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update account_move_line set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update account_voucher set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update crm_claim set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update stock_move set partner_id = %s where partner_id = %s',(pid2,pid1))
                cr.execute('update stock_picking set partner_id = %s where partner_id = %s',(pid2,pid1))
      
        return res

merge_partner()
 

Step2- Then create merge_partner.xml file in your own module and pass this file in __openerp__.py file.

Use this code given below:

<?xml version="1.0" ?>
<openerp>
    <data>
        
        <record id="view_merge_partner_form" model="ir.ui.view">
            <field name="name">merge.partner.form</field>
            <field name="model">merge.partner</field>
            <field name="type">form</field>
            <field name="arch" type="xml">
                <form string="Merge Partner Entries" >
					<field name="name1"/>
					<field name="name2"/>
					<separator colspan="4" string="Actions" col="2"/>
                    <button name="merge_on_partner" string="Merge Partner" icon="gtk-execute" type="object"/>
					<button name="delete_partner" string="Delete" icon="gtk-execute" type="object"/>
									
                </form>
            </field>
        </record>
		
		<record model="ir.actions.act_window" id="action_merge_partner_form">
			<field name="name">Merge Partners</field>
			<field name="res_model">merge.partner</field>
		</record>
		 
<menuitem name="Merge Partners" id="menu_merge_partner"/>
<menuitem name="Merge Partner" id="menu_merge" parent="merge_partner.menu_merge_partner" action="action_merge_partner_form" sequence="1"/>
	</data>
</openerp>