Create a separate table to store this data when it exists, thereby eliminating the need for odd/NULL data in the interim. This is a potentially good solution when a particular column is very sparse, ie: it is very often not entered or rarely required or present. 创建一个单独的表来存储此数据(如果存在),从而在此期间不需要奇数/ NULL数据。 当特定的列非常稀疏时,这是一个潜在的好解决方案,即:它通常不输入或很少需要或不存在。