What purpose such a massive data is required. There are millions of posts in lakhs of units if not more. If you wish to create a data bank on that you have to conduct a survey sector/field wise, industry & unit wise. You have to compare various employers' emoluments and create a directory of bench mark. Sky is the limit for fixing salary levels as it's employees' market. For a lowest salary levels there is Minimum Wages Act to what should be right levels varies from the competence of the candidates and policies of the employers. Probably you should collect data Invitations for employment published by employers & agencies and compile them to suit your requirement, and there are lots of sites to help you.