Normalize table

Question

I am wondering how to normalize table like this:

field1|field2|field3
text1 |txt2  | 1,2,5
other1|other2| 1,8,7

field1 will repeat many times , field2 is unique(won't repeat) , field 3 - users id. Something like favorites.

Answer 1

Give a primary key for this table and create a new one with field3+this key.

Master table (your original table after the modification)

field1 | field2 | fID
...    | ...    | 1
...    | ...    | 2

Favorites table:

fID | field3
1   | 1
1   | 2
1   | 5
2   | 1
... | ...

Selecting data

You can use JOIN or just a WHERE to get the results. Let's say

SELECT field3 FROM Favorites WHERE fID = 1

gets

1,2,5

So if I'm not wrong your question is related to the master-details/parent-child pattern.

Resources

• http://www.ebruni.it/en/software/os/webgui/sqledit/examples/master_detail.htm
• Parent Child table record - Building SQL query

Answer 2

First, if field 2 is unique, then it should be declared as the primary key (or, at the very least a unique index).

Secondly, the fact that you have multiple values in field3 tells you that field3 should become a separate table linked back (related) to the first table using some unique value (which we just decided is field2).

So, your database creation script would look like this:

CREATE TABLE MainTable (field2 VARCHAR NOT NULL PRIMARY KEY, field1 VARCHAR)

CREATE TABLE OtherTable (field2 VARCHAR REFERENCES MainTable, field3 INTEGER)

You might also consider adding a separate primary key value to the second value or make field2 and field3 together a primary key.