====== SQL design tool ======

  * Entity-Relationship diagram maker:
    * yed: http://www.yworks.com/en/index.html
      * yED graph editor: http://www.yworks.com/en/products_yed_about.html
    * MySQL workbench: http://www.mysql.com/products/workbench/

  * sqlite tool in firefox
    * https://addons.mozilla.org/en-US/firefox/addon/sqlite-manager/

  * sqlite desktop tool
    * DB Browser for SQLite: https://sqlitebrowser.org/
====== database algebra ======

  * symbols: http://en.wikipedia.org/wiki/Relational_algebra

====== Field Type ======

  * int: integer; length: how many digits.
  * AI: auto incremental
  * varchar: characters; length: how many characters to enter (128)
  * date: enter it yourself or current timestamp
  * float(n,d): n for length, and d for decimal point from right

Prime vs Unique:
  * Prime for data linking
  * Unique for indexing and searching

  * BLOB type: a binary data type, "binary large object"
    * read and write photo file in DB: http://www.mysqltutorial.org/python-mysql-blob/