Removed duplicated sentence: "This is the core of the entire SQL layer. After a SQL statement is parsed to an abstract syntax tree (AST), the query plan is generated and optimized (including logical optimization and physical optimization) in this package."
Removed duplicated sentence: "This is the core of the entire SQL layer. After a SQL statement is parsed to an abstract syntax tree (AST), the query plan is generated and optimized (including logical optimization and physical optimization) in this package."