On the basis of introducing substitution principle and its functions briefly, the thesis discusses important positions and applications of substitution principle in appraisal of real estate, It is pointed out that substitution principle is a general principle in guiding appraisal of real estate and an essential principle, it is widely used in appraisal of real estate.

This article first introduced SQL injection principle, explained the general idea of SQL injection, followed by a number of ways to introduce the hazards of SQL injection on the hospital website.