Dplyr通过=（a = b）连接，其中a和b是包含字符串的变量？

I am trying to perform an inner join two tables using dplyr, and I think I'm getting tripped up by non-standard evaluation rules. When using the by=("a" = "b") argument, everything works as expected when "a" and "b" are actual strings. Here's a toy example that works:I am trying to perform an inner join two tables