SELECT SI.customer as cname,SI.invoicing_type,M.name,
M.supply_id,M.zone,M.area,
SI.customer_name as customerName,
M.meter_type as meter_type,
SI.invoicing_type as invoicing_type,
SI.name As invoiceName,
SI.grand_total AS 'totalBilled',
SI.paid_amount AS 'totalPaid',
SI.outstanding_amount AS 'outstandingBalance',
SI.modified AS 'modified',
SI.owner AS 'created_by',
SI.status AS 'invoiceStatus',
SI.posting_date AS 'posting_date'
FROM `tabSales Invoice` SI 
Left join tabMeter M on M.name=SI.meter_name where SI.meter_name IS NULL