Databases - SQLite Wrap-Up

Transcription

1 Databases - SQLite Wrap-Up MCS 275 Danko Adrovic (UIC) MCS 275 April 8, / 11

2 SQLite Advanced Operations A common SQL command SELECT * FROM some-table SELECT some-column FROM some-table Now we want to take a second look at other, more advanced commands filter queries with WHERE sort data with ORDER BY get unique items with DISTINCT update records with UPDATE delete records with DELETE Danko Adrovic (UIC) MCS 275 April 8, / 11

3 Databases title rating system year Tales of the Abyss T 3DS 2011 Adventure Time E10+ 3DS 2012 Hollywood Crimes T 3DS 2011 Forza Motorsport 4 E Sonic Generations E Forza Horizon T ZhuZhu Pets E Wii 2012 Danko Adrovic (UIC) MCS 275 April 8, / 11

4 Filtering with WHERE WHERE statement is placed at the end of the SQL statement it allows you to filter elements when you make a call to your database only a subset of elements is returned typical use: sql = FROM tablename SELECT column WHERE boolean statement WHERE can be used to check for equality, inequality, greater than, less than, to find items that are similar selecting games with rating E: SELECT * FROM games WHERE rating= E selecting games with rating is not E: SELECT * FROM games WHERE rating!= E Danko Adrovic (UIC) MCS 275 April 8, / 11

5 Using LIKE to Find Similar Items SELECT * FROM table WHERE column LIKE %string % sign is there to create a pattern that the database will try to match to % sign indicates where SQLite is allowed to fill in any other characters % sign can go either at the beginning of a substring, at the end, or both Examples LIKE red% would select: red light, red, reddish would not select: light red, credo LIKE %red would select: light red, red would not select: red light, reddish, credo LIKE %red% would select: red light, red, reddish, credo would not select: Red in our table: sql = SELECT * FROM games WHERE rating LIKE E% would return all E rated games as well as E10+ rated games Danko Adrovic (UIC) MCS 275 April 8, / 11

6 Using NOT LIKE to Find Non-Similar Items Example SELECT * FROM table WHERE column NOT LIKE %pattern% when we use NOT, the database will return every item that does not match that pattern in our table: sql = SELECT * FROM games WHERE rating NOT LIKE E% would return all games except those rated E and E10+ Danko Adrovic (UIC) MCS 275 April 8, / 11

7 Querying with Greater/Less Than or Equal Example SELECT * FROM table WHERE column > value SELECT * FROM table WHERE column >= value SELECT * FROM table WHERE column < value SELECT * FROM table WHERE column <= value in our table: sql = SELECT title FROM games WHERE year > 2011 in our table: sql = SELECT title FROM games WHERE year >= 2011 in our table: sql = SELECT title FROM games WHERE year < 2011 in our table: sql = SELECT title FROM games WHERE year <= 2011 Danko Adrovic (UIC) MCS 275 April 8, / 11

8 Sorting with ORDER BY So far our returned items where not listed in any specific order. We can return items in a specific order, with the ORDER BY command. SELECT * FROM table ORDER BY column Examples (ascending order) the following returns titles sorted in alphabetical order sql = SELECT titles FROM games ORDER BY title Examples (descending order) the following returns titles sorted in reversed alphabetical order sql = SELECT titles FROM games ORDER BY title DESC Danko Adrovic (UIC) MCS 275 April 8, / 11

9 Getting Unique Items with DISTINCT When we use DISTINCT with a SELECT statement, the database returns only unique entries for that column. Example SELECT DISTINCT column FROM table sql = SELECT DISTINCT system FROM games returns: [(360,), (3DS,), (Wii,)] we have games for Xbox 360, Nintendo 3DS, and Wii Danko Adrovic (UIC) MCS 275 April 8, / 11

10 Updating Records with UPDATE When we use the UPDATE command, we can change records/entries inside a database. UPDATE table SET column= some value WHERE column= some value Example: we want to add another game to the database sql = INSERT INTO games (title, rating, system, year) VALUES ( Luigi s Mansion, E, 3DS,2013) However, we later realize that the game is called Luigi s Mansion, Dark Moon, so we update that particular entry! sql = UPDATE games SET title= Luigi s Mansion, Dark Moon WHERE title= Luigi s Mansion Danko Adrovic (UIC) MCS 275 April 8, / 11

11 Deleting Records with DELETE When we use the DELETE command, we can remove a record from the database entirely. DELETE FROM table WHERE column=value Example: Let s say we want to delete the game Hollywood Crimes from our database. sql = DELETE FROM games WHERE title=hollywood Crimes To check whether the game is still in the database, you can run command sql = SELECT * FROM games WHERE title= Hollywood Crimes when the game is not there, this will return [ ] Danko Adrovic (UIC) MCS 275 April 8, / 11