通过 MySQL 上的索引表获取值

Question

我有两个表：

Table1 (id, name, var1, var2, var3)

Vars (id, name)

附实例行数：

Table1:

1, John, 3, 6, 7
2, Peter, 1, 4, 3

Table 两个（变量）：

1, Cat
2, Dog
3, Fish
4, Cow
5, Goat
6, Bear
7, Bird
8, Koala
9, Lion
10, Frog

期望的输出是：

1, John, Fish, Bear, Bird
2, Peter, Cat, Cow, Fish

我尝试使用一些 INNER JOINS 但我认为我做错了，因为我无法获得正确的结果，我该如何实现？谢谢

Answer 1

您需要 join vars table 三次。或者与一行中变量的数量一样多。

select t1.id, t1.name, v1.name, v2.name, v3.name
from table1 t1
join vars v1 on v1.id = t1.var1
join vars v2 on v2.id = t1.var2
join vars v3 on v3.id = t1.var3

Answer 2

使用LEFT JOIN处理缺失值：

SELECT t1.id, t1.name, v1.name AS name_1, v2.name AS name_2, v3.name AS name_3
FROM Table1 t1
LEFT JOIN Vars v1
  ON t1.var1 = v1.id
LEFT JOIN Vars v2
  ON t1.var2 = v2.id
LEFT JOIN Vars v3
  ON t1.var3 = v3.id

通过 MySQL 上的索引表获取值

Get values by index tables on MySQL

mysql

sql

inner-join

relational-database