Example of mysql alter statement usage

/ / the primary key
ALTER TABLE tablename add new_field_id int(5) UNSIGNED DEFAULT 0 NOT NULL anto_increment,ADD PRIMARY KEY (new_field_id);

// add a new column
mysql > ALTER TABLE tablename ADD fieldname fieldtype
Such as:
ALTER TABLE t2 ADD d TIMESTAMP;
ALTER TABLE infos ADD ex TINYINT NOT NULL DEFAULT '0';

/ / delete columns
mysql > ALTER TABLE table_name DROP field_name
Such as:
ALTER TABLE t2 DROP COLUMN c;

// modify the original field name and type
mysql > ALTER TABLE tablename CHANGE old_field_name new_field_name field_type;
Such as:

// rename the column
ALTER TABLE t1 CHANGE a b INTEGER;

// change the type of the column
ALTER TABLE t1 CHANGE b b BIGINT NOT NULL;
ALTER TABLE infos CHANGE list list TINYINT NOT NULL DEFAULT '0';

// rename the table
ALTER TABLE t1 RENAME t2;

/ / add index
mysql > ALTER TABLE tablename CHANGE depno depno int(5) NOT NULL;
mysql > ALTER TABLE tablename ADD INDEX index name (field name 1[, field name 2...] );
mysql > ALTER TABLE tablename ADD INDEX emp_name(name);

// plus the search of the main keyword
mysql > ALTER TABLE tablename ADD PRIMARY KEY(id);

// plus index with only 1 constraint
mysql > ALTER TABLE tablename ADD UNIQUE emp_name2(cardnumber);

// drop an index
mysql > ALTER TABLE tablename DROP INDEX emp_name;