Add auto_increment to existing column in mysql

                     Auto_ increment is used to increase by 1 while insert a new data to mysql table. The auto increment column must be defined as key.

Create table with auto_increment in mysql:

                      You can add auto_increment while creating new table. The mysql query is:

                       CREATE TABLE table1 

                               (No int(5) NOT NULL AUTO_INCREMENT PRIMARY KEY, 

                                 Game_name varchar(15), Image varchar(15)) 

Now the table is created with auto increment.

Add auto_increment to existing column in mysql:

                      You created a table in which the column with specific definitions in mysql. You created table column without auto increment. Then how can you add it to existing column in mysql.  The following mysql query is used to add auto increment to existing column in mysql.

Mysql Query:

                         Alter table table_name modify column_name datatype(length) AUTO_INCREMENT PRIMARY KEY

Consider the example:
The structure of table1 in database new look like this:

                         Now we are going to add auto increment to column 'No' in mysql table 'table1'.  The mysql query is:

                     Alter table table1 modify No int(5) AUTO_INCREMENT PRIMARY KEY

Now your structure look like this:

     Now you can see the column name 'No' is auto increment. Suppose  your mysql query like below:

     Alter table table1 modify No int(5) AUTO_INCREMENT

Then you'll get error like this:

                                 So you should be add 'AUTO_INCREMENT' with 'PRIMARY KEY' in mysql table.

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Change column with NOT NULL to NULL in mysql

                       You created a table in which the column with 'NOT NULL'. Suppose you want to change mysql column definition from 'NOT NULL' to 'NULL'. Then how can you change it in mysql. The following mysql query is used to change column from 'NOT NULL' to 'NULL' in mysql.

Mysql Query:

                         Alter table table_name 
                            change column_name column_name datatype(length) definition

Change column NOT NULL to NULL in mysql:

Consider the example:
The structure of table1 in database new look like this:

       
                Where, the column name 'No' is NOT NULL. You can see the Null column value is No in above mysql table at first row.  Now we are going to change column 'NOT NULL' to 'NULL' in mysql table 'table1'.  The mysql query is:

                 
                           Alter table table1 change No No int(5) NULL

Now your structure look like this:

                            Now you can see the column name 'No' is NULL.

Change column NULL to NOT NULL in mysql:

                                         Similarly you can change the column definition from NULL to NOT NULL. The mysql query as follows as:

                                            Alter table table1 change No No int(5) NOT NULL

                        Now the column 'No' changed NULL to NOT NULL.

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Change column datatype in mysql

                       You created a table with column in specific datatype. Sometimes you need to change datatype of column. At the time, you can modify the datatype of field. It is possible in mysql. The following mysql query is used for this:

Mysql Query:

                         Alter table table_name modify column_name datatype(length)

Consider the example:
 table1 is name of this table.

When you click the structure of table in your database, it is look like this:

                          Suppose you've to change datatype of column 'Game_name'. On that time you can change the field type. The mysql query is:

                     Alter table table1 modify Game_name char(15)

Now your structure look like this:

     Now your Game_name column type is changed from varchar into char.

Changing the multiple column datatype at the time in mysql:

                      You can change multiple column datatype at a time in mysql. The mysql query as follow as:

Mysql Query:

                          Alter table table1
                                    modify No varchar(5),

                                    modify Game_name char(15),

                                    modify Image char(15)

                          Now your output look like this:

                          Now you will get output column 'No' with varchar, 'Game_name' with char and 'Image' with char in your mysql table.

Datatypes in mysql:

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Changing the column size in mysql

                       You created a table with specific size of column. Sometimes you need to increase the size of column, if the size is not enough. At the time, you can modify the size of field. It is possible in mysql. The following mysql query is used for this:

Mysql Query:

                         Alter table table_name modify column_name datatype(length)

Consider the example:
 table1 is name of this table.

When you click the structure of table in your database. It is look like this:

                          Suppose you've to add more characters to column Game_name. On that time you can change the field size. The mysql query is:
                     Alter table table1 modify Game_name varchar(40)  

Now your structure look like this:

     Now your Game_name column size is changed into 40.

Changing the multiple column size at the time in mysql:

                      You can change multiple column size at a time in mysql. The mysql query as follow as:

Mysql Query:

                          Alter table table1

                                    modify Game_name varchar(50),

                                    modify Image varchar(40)

                          Now your output look like this:

                          Now you will get output as Game_name with 50 size and Image with 40 size.

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