This function is used to get the character from a text field .
Syntax In MySQL :

select mid ( column_name , start [ starting_length , ending_length ] ) from table_name ;

Starting length : It is mandatory .
Ending length : It is optional . If you omit the ending length then it will return entire length of that character .
Syntax in SQL :

select substring ( column_name , start , length ) from table_name ;

Example :
Table name : Employee_Info

  Id        Employee_name          Employee_Age               Employee _Salary
  1            Mukesh                  23                           100000
  2            Ayush                   24                           200000
  3            Ishan                   20                           400000
  4            Pranav                  35                           700000
  5            Abhishek                26                           800000
  6            Ravi                    25                           300000
  7            David                   40                           800000

Query to extract substring from original string .

select mid ( Employee_name , 1 , 3 ) from Employee_Info ;

Output :

 Employee_name
  Muk
  Ayu
  Ish
  Pra
  Abh
  Rav
  Dav