alter_table_statement 

<alter_table_statement> ::=
  ALTER TABLE <table_name> <add_definition>
| ALTER TABLE <table_name> <alter_definition>
| ALTER TABLE <table_name> <column_change_definition>
| ALTER TABLE <table_name> <drop_definition>
| ALTER TABLE <table_name> <modify_definition>
| ALTER TABLE <table_name> <referential_constraint_definition>
| ALTER TABLE <table_name> <sample_definition>