什么是传递依赖
当间接关系导致函数依赖时，称为传递依赖。
如果 P -> Q 和 Q -> R 为真，那么 P-> R 是传递依赖。
要实现 3NF，消除传递依赖。
示例
<MovieListing>
| Movie_ID td> | Listing_ID | Listing_Type | DVD_Price ($) | |
| M08 | L09 > | 犯罪 | 180 > | |
| M03 | M03 | L05 | 戏剧 | 250 |
| M05 | L09 | 犯罪 | 180 |
上表不在3NF，因为它具有传递函数依赖 -
| Movie_ID -> Listing_ID Listing_ID -> Listing_Type |
因此，以下具有传递函数依赖性。
Movie_ID -> Listing_Type
The above states the relation <MovieListing> violates the 3rd Normal Form (3NF).
To remove the violation, you need to split the tables and remove the transitive functional dependency.
<Movie>
Movie_ID
| Listing_ID | DVD_Price ($) | |
| M08 | L09 | 180 |
| M03 | L05 | 250 |
| M05 | L09 | 180 |
<Listing>
Listing_ID
| Listing_Type | |
| L09 | Crime |
| L05 | Drama |
| L09 | Crime |
Now the above relation is in Third Normal Form (3NF) of Normalization.
