Clear demo transactions from an Odoo database

delete from crm_lead;

delete from purchase_order_line;
delete from purchase_order;

delete from sale_order_line;
delete from sale_order;

delete from procurement_order;
delete from procurement_group;

delete from stock_move;
delete from stock_move_line;
delete from stock_pack_operation;
delete from stock_pack_operation_lot;
delete from stock_picking;
delete from stock_inventory_revaluation_quant;
delete from stock_quant;
delete from stock_production_lot;
delete from stock_inventory_line;
delete from stock_inventory;
delete from stock_landed_cost;
delete from stock_landed_cost_lines;
delete from stock_inventory_revaluation_quant;
delete from stock_inventory_revaluation;
delete from stock_valuation_adjustment_lines;
delete from stock_change_product_qty;

delete from account_partial_reconcile;
delete from account_move_line;
delete from account_invoice;
delete from account_invoice_line;
delete from account_move;
delete from account_payment;
delete from account_payment_diff_register;
delete from account_full_reconcile;
delete from account_analytic_line;

delete from mrp_production;
delete from mrp_production_product_line;
delete from product_price_history;
delete from product_barcode;
delete from mrp_bom WHERE;

delete from qc_inspection; 
delete from qc_inspection_line;

Check:
product_price_history
mail_messages
reset sequences
ir_attachment