SQL Update statement is used to modify the records in table in database . We can modify either by change data or deleting data or to update the existing data .
We can modify the rows based on condition and condition come with where clause .
Syntax :

update table_name set column_name = value1 ,............column_nameN = valueN , where clause ;

Example :

Table name : Employee_Info

 Employee_name            Employee_Age          Employee _Salary
      Mukesh                  23                           100000
      Ayush                   24                           200000
      Ishan                   20                           400000
      Pranav                  35                           700000
      Abhishek                26                           800000
      Ravi                    25                           300000
      David                   40                           800000

If i want to update the salary of Mukesh then you can use below query :

update Employee_Info set Employee_Salary = ' 900000 ' where Employee_name = ' Mukesh ' ;

Output :

 Employee_name            Employee_Age          Employee _Salary
      Mukesh                  23                         **900000** // After updation
      Ayush                   24                           200000
      Ishan                   20                           400000
      Pranav                  35                           700000
      Abhishek                26                           800000
      Ravi                    25                           300000
      David                   40                           800000

Using this statement we can update multiple column also , see below :

update Employee_Info set Employee_Salary = ' 10,00000 ' , Employee_Age = ' 40 ' where Employee_name = ' Abhishek ' ;

Output :

 Employee_name            Employee_Age          Employee _Salary
      Mukesh                  23                           100000
      Ayush                   24                           200000
      Ishan                   20                           400000
      Pranav                  35                           700000
      Abhishek                **40**                     **10,00000** // After updation
      Ravi                    25                           300000
      David                   40                           800000