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 DDLData Definition Language (DDL) statements are used to define the database structure or schema. Some examples: CREATE - to create objects in the databaseALTER - alters the structure of...

select to_char(sysdate,'yyyy') from dual; --年select to_char(sysdate,'Q' from dual; --季select to_char(sysdate,'mm') from dual; --月select to_char(sysdate,'dd') from dual; --日ddd 年中的第几天WW 年中的第几...