Edit table field name/Field length/fields type in MySQL

Let's take a look at the usual methods.

MySQL's simple syntax, commonly used, but not easy to remember. Of course, these SQL syntaxes are basically generic in each database. Listed below:

1. Add a field

ALTER TABLE user add COLUMN new1 VARCHAR DEFAULT NULL; Add a field, the default is empty
ALTER TABLE user add COLUMN new2 VARCHAR is not NULL; Add a field, default cannot be empty

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, you must now restart

Primary key

ALTER TABLE tabelname add new_field_id int (5) unsigned default 0 NOT NULL auto_increment, add primary key (NEW_FIELD_ID);

Add a new column

ALTER TABLE T2 add d timestamp;
ALTER TABLE infos add ex tinyint NOT null default ' 0′;

Delete Column

ALTER TABLE T2 drop column C;

renaming columns

ALTER TABLE T1 change a b integer;

Change the type of a column

ALTER TABLE T1 change b b bigint not null;
ALTER TABLE infos change list tinyint not null default ' 0′;

Renaming tables

ALTER TABLE t1 rename T2;

Add index

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 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 fields:

mysql> ALTER TABLE table_name ADD field_name Field_type;

To 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 (30)

can use

ALTER TABLE user modify column name varchar (50);