The syntax for table constraints in BNF is as follows:

Syntax

table_constraint ::=
 [ CONSTRAINT constraint_name]
   PRIMARY KEY ( column[, ...] )
     | UNIQUE ( column[, ...] )
     | FOREIGN KEY ( column[, ...] )
      REFERENCES [owner_name.]table_name[ ( column[, ...] ) ]
     | CHECK ( search_condition )

For more information, see Table constraints.