单独一个表中coalesce是可以对缺失值进行填充的,但在多表查询对照时,对coalesce的使用不太明白,请大家能解释下下面这段代码中coalesce的作用什么嘛?
proc sql outobs=10;
title 'Populations and/or Coordinates of World Cities';
select coalesce(Capital, City,Name)format=$20. 'City',
coalesce(Name, Country) format=$20. 'Country',
Population, Latitude, Longitude
from sql.countries full join sql.worldcitycoords
on Capital = City and
Name = Country;