MySQL table field adjustment

New field format ：
ALTER TABLE Table name ADD Field name Field type （ Field length - optional ） CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL（ Can't be empty ） DEFAULT 0（ The default value is ） COMMENT ' remarks '  AFTER After specifying the field ( No default last );
 
New examples ：
ALTER TABLE table_name ADD COLUMN age varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL DEFAULT 0  COMMENT ' Age ' AFTER name;
 
Modify field format :
ALTER TABLE table_name MODIFY COLUMN Field name New data types New type length New default New notes ;
-- COLUMN Keywords can be omitted
 
Modify field example :
ALTER TABLE table_name MODIFY COLUMN 'column' decimal (15,2) DEFAULT NULL COMMENT ' notes '; -- normal , Can modify the field type 、 Type length 、 The default value is 、 notes
 
Change the field type to unsigned :
ALTER TABLE table_name MODIFY COLUMN 'column' BIGINT(11) UNSIGNED DEFAULT '0' COMMENT ' notes ';
 
ALTER TABLE Table name CHANGE [column] Old field name new field name New data types ;     
alter table table_name change old_column new_column varchar(100) DEFAULT '1.2' COMMENT ' notes '; -- normal , At this time, the field name has not changed , Can modify the field type 、 Type length 、 The default value is 、 notes
 
 
Modify table defaults If there is a default value, delete it first and then modify it
alter table table_name alter column column drop default; 
alter table table_name alter column column set default '0';