DROP DEFAULT SINGLE TABLE RULE 语法用于删除默认的单表规则
DROP DEFAULT SINGLE TABLE RULE
DropDefaultSingleTableRule ::= 'DROP' 'DEFAULT' 'SINGLE' 'TABLE' 'RULE' ifExists? ifExists ::= 'IF' 'EXISTS'
DROP DEFAULT SINGLE TABLE RULE;
DROP、SHARDING、SINGLE、TABLE、RULE
DROP
SHARDING
SINGLE
TABLE
RULE