MySQL database table modifies the type of a column

listed below:
1. Add a field
ALTER TABLE user add COLUMN new1 VARCHAR default null;//Add a field that defaults to null
ALTER TABLE user add COLUMN new2 VARCHAR (a) not NULL; Add a field that cannot be empty by default
2. Delete a field
ALTER TABLE user DROP COLUMN new2; Delete a field
3. Modify a field
ALTER TABLE user MODIFY New1 VARCHAR (10); Modify the type of a field
ALTER TABLE user change new1 new4 int; To modify the name of a field, be sure to re -

//PRIMARY key
ALTER TABLE tabelname add new_field_id int (5) unsigned default 0 NOT NULL auto_increment, add primary key (New_field_i d);
//Add a new column
ALTER TABLE T2 add d timestamp;
ALTER TABLE infos add ex tinyint NOT null default ' 0′;
//Delete columns
ALTER TABLE T2 drop column C;
//Rename columns
ALTER TABLE T1 change a b integer;
//Change the type of column
ALTER TABLE T1 change b b bigint not null;
ALTER TABLE infos change list list tinyint not null default ' 0′;
//Rename table
ALTER TABLE t1 rename T2;
Gazzo Primer
mysql> ALTER TABLE tablename change depno depno int (5) is 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);
index of the plus primary keyword
mysql> ALTER TABLE tablename ADD PRIMARY key (ID);
index with unique restriction criteria
mysql> ALTER TABLE tablename add unique emp_name2 (cardnumber);
Delete an index
mysql>alter Table tablename DROP index emp_name;
Add Field:
mysql> ALTER TABLE table_name ADD field_name field_type;
Modify the original field name and type:
mysql> ALTER TABLE table_name change old_field_name new_field_name field_type;
To delete a field:
mysql> ALTER TABLE table_name DROP field_name;
MySQL Modify field length
ALTER TABLE name modify column field name type;
For example
The User table name field in the database is varchar (
can be used
ALTER TABLE user modify column name varchar ();

Or

ALTER TABLE user modify column name datetime;

MySQL database table modifies the type of a column