Some useful commands of MySql

• Add a column to an existing MySQL table : MySQL tables are easy to extend with additional columns. To add a column called email to table type the following command:

ALTER TABLE tablename ADD email VARCHAR(20);

• To insert the new column after a specific column, such as name, use this statement:

ALTER TABLE tablename ADD email VARCHAR(20) AFTER name;

• If you want the new column to be first, use this statement:

ALTER TABLE tablename ADD email VARCHAR(20) FIRST;

• Query to alter column data type of the table: The Alter Query redefine the table  and change the data type of column ’empid’.

mysql> alter table tablename change empid empid varchar(100);

• To see what types and values you specify for each field. You give the following command. The describe employee describe the field name ,data type ,null ,key etc in table.

mysql> describe tablename;

• To see myql version:

select version();

or

SHOW VARIABLE LIKE “%version%”;

• To load data from a file in Mysql

LOAD DATA LOCAL INFILE ‘form.txt’ INTO TABLE form;

• Column delete:

alter table tablename drop column rollno;

• Multiple Column delete:

ALTER TABLE tablename Drop (column1,column2,column3);