US Patent 9519774 Systems and methods for SQL query constraint solving

The present invention relates to systems and methods for analyzing SQL queries for constraint violations, which may indicate injection attacks. The systems and methods tokenize a SQL query to generate a token stream. Next, lexical nodes are generated by iterating over the token stream. Then, a parse tree can be constructed by iterating over the lexical nodes. The parse tree may be compared to a SQL schema and access configuration for a database in order to analyze the SQL query for constraint violations, including determining the number of queries in the parse tree, identifying invalid fields and table access, identifying invalid field type comparisons and pattern matches, and identifying early statement termination.