merging-tables-sql.txt

**Primary Key** - must be unique, something that is not reproduced anywhere else in a table; can be used to reference this table in other tables
**Foreign Key** - key used from another table

**table relationships**
- 1 to 1 (character to wand)
- 1 to many (character can only be in one house, house can have many characters)
- many to many (characters to books, character in multiple books, one book has multiple characters)

 **Entity Relationship Diagram**
 ______________________________
|       characters             |
|______________________________|
|     |             |          |
|  PK |  id         | serial   |
|     |  name       | varchar  |
|  FK |  house      | number   | >-----
 ------------------------------        |
                                       |
 _________________________________     |
|         houses                  |    |
|_________________________________|    |
|     |                |          |    |
|  PK |  id            | serial   |-|--
|     |  house         | varchar  | 
|     |  founder       | varchar  | 
 ---------------------------------
 
 **Creating a Join**
 Select = Read (can create, insert, etc)
 * - all columns
 from <table name>
 join <table name>
 on <matching-ids>
  
 ```select * from characters on characters.house = houses.id