Tag: join

INNER JOIN ON与WHERE子句

为了简单起见，假定所有相关的字段都不是NULL。 你可以做： SELECT table1.this, table2.that, table2.somethingelse FROM table1, table2 WHERE table1.foreignkey = table2.primarykey AND (some other conditions) 要不然： SELECT table1.this, table2.that, table2.somethingelse FROM table1 INNER JOIN table2 ON table1.foreignkey = table2.primarykey WHERE (some other conditions) 这两个工作在MySQL的相同方式吗？

“INNER JOIN”和“OUTER JOIN”有什么区别？

另外如何做LEFT JOIN ， RIGHT JOIN和FULL JOIN适合？

如何join（合并）数据框架（内部，外部，左，右）？

给定两个dataframe： df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3))) df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1))) df1 # CustomerId Product # 1 Toaster # 2 Toaster # 3 Toaster # 4 Radio # 5 Radio # 6 Radio df2 # CustomerId State # 2 Alabama # […]