There are 4 kinds of formulas, 1nf, 2nf, 3nf, bcnf (the first 3 known as the word X paradigm, the fourth forgotten what it means, BC seems to be a human name), according to the order from left to right, one is more than one The requirements are more stringent. It is necessary to meet a paradigm to meet all paradigms in front of her. The general project's database design can reach 3NF, and redundancy can be appropriately increased according to the specific situation, and the so-called specification is not required.
To put it bluntly, 1NF is required to only put each other in a table, do not put the direction of the wind, the number of horses and the number of cattle in a table, this is just the most basic requirements, in fact, do not say No one will do this. As for 2nf, 3nf, BCNF although the content described is different, it is very similar to the data characteristics, it is like telling about the girl's name. (B), the bust (c) is placed in the same table, ie, do not use ABC a table, but should use AB, BC to try to avoid waste of data storage space. Because and the same girl may date a few times, but it is not necessary to record her bust every time.
