帮助文件中的一个符号问题
CREATE TABLE
[ database_name.[ owner ] .| owner.] table_name
( { < column_definition >
| column_name AS computed_column_expression
| < table_constraint > ::= [ CONSTRAINT constraint_name ] }
| [ { PRIMARY KEY | UNIQUE } [ ,...n ]
)
如上所示的“::=”这个符号什么意思，书上没有将，虽然有点明白的样子，但是还是很迷糊，不知道有人知道不？
[ database_name.[ owner ] .| owner.] table_name
( { < column_definition >
| column_name AS computed_column_expression
| < table_constraint > ::= [ CONSTRAINT constraint_name ] }
| [ { PRIMARY KEY | UNIQUE } [ ,...n ]
)
