Check out example codes for "my sql alter table". It will help you in understanding the concepts better.

Code Example 1

ALTER TABLE contacts
  ADD last_name varchar(40) NOT NULL
    AFTER contact_id,
  ADD first_name varchar(35) NULL
    AFTER last_name;

Code Example 2

ALTER TABLE nom_table
MODIFY nom_colonne type_donnees

Code Example 3

ALTER TABLE nom_table
DROP nom_colonne

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