MyBatis explore the difference between the symbols $ and # ----- interface class mapping XML file

   1. The difference between the $ and #

• $ # {} {} And can get the value in the map object property value or pojo
• # {}: Is pre-compiled form, set the parameter to the sql statement, preventing sql injection
• $ {}: Value taken directly assembled in the sql statement; poses security issues

   2. $ # and usage

2.1 table, sorting as a variable, you must use $ {}

select * from ${year}_salary where xxx;

select * from tbl_employee order by ${f_name} ${order}

# {2.2} can be used to place a # {}

Interface mapping file SQL statement: select * from t_employee where empId = $ {empId} and empName = # {empName}
execute precompiled SQL statement: select * from t_employee where empId = 2 and empName =?