access中基本表的结构的修改命令

ALTER TABLE table { [ ALTER COLUMN column_name { new_data_type [ ( precision [ , scale ] ) ] [ COLLATE < collation_name > ] [ NULL | NOT NULL ] | {ADD | DROP } ROWGUIDCOL } ] | ADD { [ < column_definition > ] | column_name AS computed_column_expression } [ , ...n ] | [ WITH CHECK | WITH NOCHECK ] ADD { < table_constraint > } [ , ...n ] | DROP { [ CONSTRAINT ] constraint_name | COLUMN column } [ , ...n ] | { CHECK | NOCHECK } CONSTRAINT { ALL | constraint_name [ , ...n ] } | { ENABLE | DISABLE } TRIGGER { ALL | trigger_name [ , ...n ] } } < column_definition > ::= { column_name data_type } [ [ DEFAULT constant_expression ] [ WITH VALUES ] | [ IDENTITY [ ( seed , increment ) [ NOT FOR REPLICATION ] ] ] ] [ ROWGUIDCOL ] [ COLLATE < collation_name > ] [ < column_constraint > ] [ ...n ] < column_constraint > ::= [ CONSTRAINT constraint_name ] { [ NULL | NOT NULL ] | [ { PRIMARY KEY | UNIQUE } [ CLUSTERED | NONCLUSTERED ] [ WITH FILLFACTOR = fillfactor ] [ ON { filegroup | DEFAULT } ] ] | [ [ FOREIGN KEY ] REFERENCES ref_table [ ( ref_column ) ] [ ON DELETE { CASCADE | NO ACTION } ] [ ON UPDATE { CASCADE | NO ACTION } ] [ NOT FOR REPLICATION ] ] | CHECK [ NOT FOR REPLICATION ] ( logical_expression ) } < table_constraint > ::= [ CONSTRAINT constraint_name ] { [ { PRIMARY KEY | UNIQUE } [ CLUSTERED | NONCLUSTERED ] { ( column [ , ...n ] ) } [ WITH FILLFACTOR = fillfactor ] [ ON { filegroup | DEFAULT } ] ] | FOREIGN KEY [ ( column [ , ...n ] ) ] REFERENCES ref_table [ ( ref_column [ , ...n ] ) ] [ ON DELETE { CASCADE | NO ACTION } ] [ ON UPDATE { CASCADE | NO ACTION } ] [ NOT FOR REPLICATION ] | DEFAULT constant_expression [ FOR column ] [ WITH VALUES ] | CHECK [ NOT FOR REPLICATION ] ( search_conditions )