Exam:
--------

On monday!


Important:
-----------------

Please whitelist the following email: rpidbsprof@gmail.com

Instructions are here:

https://itssc.rpi.edu/hc/en-us/articles/360010480672-Anti-Spam-Services-Respite-FAQ

I will send your username/password for the class db server from this
address.

SQL
--------

SQL is an industry standard

- Query language  - select from where

- Data manipulation language  - create/drop/....
       insert/update/delete tuples

- Case insensitive

- Strings are delimited by ''

- Each statemnt ends with ;

- Comments are in --

- SQL is bag based, not set based

- Relations may not have any primary keys

- Use DISTINCT if copies may be returned but not wanted

--

SELECT
   attributes
FROM
   relation
WHERE
   boolean conditions
;   


select
   id
   , title
   , viewers7day
   , firstaired
from
   episodes
where
   viewers7day >9.2
   and firstaired > date '2018-09-25'
;

Regular expressions:
-----------------------

%  zero or more characters
_  one character only

 select * from showstoppers where make like '%''%';

NULL Values
------------

There is no value for an attribute because:

- No value exists
- I don't know the value
- I don't know whether there is a value or not

select * from cuteanimals where name is null;

3 = 4     false
3 = 3     true
3 = null  unknown


unknown and false  = false
unknown and true   = unknown

unknown or false   = unknown
unknown or true    = true

not unknown        = unknown

select
   id
   , title
from
   episodes
where
   firstaired < date '2018-09-21';

date - date -> interval
date + interval -> date
date + time -> timestamp
timestamp + interval -> timestamp
time + interval -> time