Error de ejecución: 
 <br>SELECT
					SUM(valor_credito) AS total,
					COUNT(*) AS cantidad
				FROM
					grt_prepagos
				WHERE
					nit = ''
				AND convenio = 
				AND linea_credito = ''SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND linea_credito = ''' at line 9