Update command in SQL is used to change any record in the table. Records are to be manipulated or updated using update command. Conditional update is the most common type of update command used in MySQL also. You are requested to go through the SQL WHERE command before using update command as both are to be used in proper combinations. Here is one simple command but before trying this please understand the implication of this. Without using any where command (or without using any restriction) the command will change all the records of the table. So let us start with the simple command.
UPDATE student SET class='Five'
This command will change all the records of the table student and will change all the class field to Five. This is not what is required in common cases so we will be changing records based on some conditions. Now we will change all the class four students to class five. Our command should selectively update those records for which class is equal to four and will update them to five. We will use one where clause along with update command for updating the records.
UPDATE student SET class='Five' WHERE class='Four'
This command will update only those records for which class is equal to 'Four'. So this way we can update records selectively. Now let us move one more step and change the records selectively based on some value in some other field. We will change records for which class is equal to 'Four' and mark is more than 70. We will promote those students only who has got more than or equal to 70 mark.
UPDATE student SET class='Five' WHERE class='Four' and mark >= 70
This will only change the records for which class=four and mark is more than or equal to 70. We have added two conditions by using AND as a logical operator. This way we can continue with adding more AND combinations to the query. Depending on the logic requirement OR combination can be added to the WHERE clause to UPDATE the records.
Updating a password field using md5 encryption
We can update the password field with md5 encryption. To store this data we will change the length of field to 32 char. Here is a command to update password field with new md5 encrypted password.