How can i get a database of all diseases, sicknesses ,ailments etc and all its associated symptoms?
Have a look at Bioportal, which is gives a comprehensive listing of openly available coding systems in the biomedical domain. Coding systems of interest for you - among others - are:
- SNOMED-CT (Standard Nomenclature of Medicine - Clincal Terms)
- MeSH (Medical Subject Headings)
- MedDRA (Medical Dictionary for Regulatory Affairs)
- ICD9, ICD10 and upcoming ICD11
All of these are work in progress (kind-of).
Which of these is best, depends on an analysis of your requirements. I would also recommend to have a look here: http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1004743