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SELECT tb_avoir.client_id, tb_avoir.avoir, tb_avoir_utilise.avoir_utilise, SUM( IFNULL( tb_avoir.avoir, 0 ) - IFNULL( tb_avoir_utilise.avoir_utilise, 0 ) ) AS balanceFROM (SELECT invoices.client_id, invoices.type, SUM( invoice_lines.quantity * invoice_lines.unit_price * ( 1 + invoice_lines.vat /100 ) ) avoirFROM `invoice_lines`LEFT JOIN invoices ON ( invoice_lines.invoice_id = invoices.invoice_id )WHERE invoices.type =2GROUP BY `invoices`.`client_id`) AS tb_avoirLEFT JOIN (SELECT invoices.client_id, invoices.type, SUM( -1 * invoice_lines.quantity * invoice_lines.unit_price * ( 1 + invoice_lines.vat /100 ) ) avoir_utiliseFROM `invoice_lines`LEFT JOIN invoices ON ( invoice_lines.invoice_id = invoices.invoice_id )WHERE invoices.type !=2AND invoice_lines.unit_price & lt;0 GROUP BY `invoices`.`client_id`) AS tb_avoir_utilise ON tb_avoir_utilise.client_id = tb_avoir.client_id GROUP BY tb_avoir.client_id