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+====== 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/