Answers for "how to add column in existing table mysql"

mysql alter table add column

ALTER TABLE vendors ADD COLUMN phone VARCHAR(15) AFTER name;

alter table add column

ALTER TABLE table
ADD COLUMN column VARCHAR (255) NOT NULL AFTER column;

mysql add column

-- ALTER TABLE tbl_name ADD COLUMN column_name column_definition 
--		[FIRST|AFTER existing_column];
ALTER TABLE office ADD COLUMN phone VARCHAR(200) DEFAULT '000' AFTER name;
ALTER TABLE office ADD COLUMN flag INT(1) FIRST;
ALTER TABLE office ADD COLUMN last_col INT(2);	-- Last column is default position
-- ↓ Test it (Fiddle)

change data type in mysql

ALTER TABLE table_name

CHANGE COLUMN column_name column_name datatype;