Generic: alter table [table name] add [field name] field attribute default default default is an optional parameter
Add field: alter table [table name] add field name smallint default 0 Add numeric field, integer, the default value is 0
alter table [table name] add field name int default 0 Add a numeric field, long integer, the default value is 0
alter table [table name] add field name single default 0 Add a numeric field, single precision, the default value is 0
alter table [table name] add field name double default 0 Add a numeric field, double precision, the default value is 0
alter table [table name] add field name Tinyint default 0 Add a numeric field, byte type, the default value is 0
alter table [table name] add field name text [null] add memo field, [null] optional parameter
alter table [table name] add field name memo [null] add memo field, [null] optional parameter
alter table [table name] add field name varchar(N) [null] increase the size of variable-length text field to N (1～255)
alter table [table name] add field name char [null] increase fixed-length text field size is fixed to 255
alter table [table name] add field name Datetime default function to add date field, in which the function can be now(), date(), etc., indicating the default value
(The above are the most commonly used, and there are other attributes, you can refer to the data type description below)
Delete field: alter table [table name] drop field name
Modify the size of a variable-length text field: alter table [table name] alter field name varchar(N)
Drop table: drop table [table name]