Notes mysql command alter ADD: Add a table field

The Alter ADD command is used to increase the table's fields.

alter ADD command format: ALTER TABLE name add field type other;

For example, a field passtest is added to table MyClass, the type is int (4), and the default value is 0:
mysql> ALTER TABLE MyClass add passtest int (4) default ' 0 ';

1) Gazzo Primer
mysql> ALTER TABLE name add index index name (field name 1[, field Name 2 ...]);

Example: mysql> ALTER TABLE employee ADD index emp_name (name);

2) Index of the plus primary keyword
mysql> ALTER TABLE name add primary key (field name);

Example: mysql> ALTER TABLE employee ADD primary key (ID);

3) Index with unique restriction conditions
mysql> ALTER TABLE name add unique index name (field name);

Example: mysql> ALTER TABLE employee add unique emp_name2 (cardnumber);

4) Delete an index
mysql> ALTER TABLE name DROP INDEX name;

Example: Mysql>alter table employee DROP index emp_name;

5) Add Field
mysql> ALTER TABLE table_name ADD field_name field_type;

6) Modify the original field name and type
mysql> ALTER TABLE table_name change old_field_name new_field_name field_type;

7) Delete field
MySQL ALTER TABLE table_name DROP field_name;

Notes mysql command alter ADD: Add a table field