CLEAR HINT 语法用于针对当前连接,清除 hint 设置
ClearHint ::=
'CLEAR' ('SHARDING' | 'READWRITE_SPLITTING')? 'HINT'
SHARDING / READWRITE_SPLITTING 时,默认清除所有 hint 设置SHARDING 的 hint 设置CLEAR SHARDING HINT;
READWRITE_SPLITTING 的 hint 设置CLEAR READWRITE_SPLITTING HINT;
CLEAR HINT;
CLEAR、SHARDING、READWRITE_SPLITTING、HINT
