db: updating from staging

cst363/lec/lec1.md

@@ -1,25 +1,35 @@
 # lec1 
 
-## A few reasons to have them \
-And what they *require* \
-Database systems generally need support for:
-1. querying - \ 
- * Finding things \
- * Just as well structured data makes querying easier 
+## Databases introduction
 
-2. access control - \
- * who can access which data segments and what they can do with that data \
-  * reading, writing, sending, etc
+First off why do we even need a database and what do they accomplish?
 
-3. corruption prevention - \
- * mirroring/raid/parity checking/checksums/etc as some examples 
+Generally a databse will have 3 core elements to it:
+
+1. querying
+	* Finding things
+		* Just as well structured data makes querying easier 
+
+2. access control 
+	* who can access which data segments and what they can do with that data 
+		* reading, writing, sending, etc
+
+3. corruption prevention
+	* mirroring/raid/parity checking/checksums/etc as some examples 
+
+## Modeling Data
 
-## Modeling Data \
 Just like other data problems we can choose what model we use to deal with data.
+In the case for sqlite3 the main data model we have are tables, where we store our pertinent data, and later we'll learn even data about our data is stored in tables.
 
-__Schema__ is the deisgn or structure of a specific database. While the __instance__ is the occurance of that schema with some data inside the fields. _The data inside those fields at this point don't really matter. \
+Because everything goes into a table, it means we also have to have a plan for _how_ we want to lay out our data in the table.
+The __schema__ is that design/structure for our databse.
+The __instance__ is the occurance of that schema with some data inside the fields, i.e. we have a table sitting somewhere in the databse which follows the given structure of a aforemention schema.
 
-__Queries__ are typically known to be declarative; typically we don't care about what goes on behind the scenes in practice since by this point we are assuming we have tools we trust and know to be somewhat efficient. \
+__Queries__ are typically known to be declarative; typically we don't care about what goes on behind the scenes in practice since by this point we are assuming we have tools we trust and know to be somewhat efficient.
 
-__Transactions__ are a set of operations. Transactions are not alllowed to fail. If _anything_ fails then everything should be undone and the state should revert to previous state.
+Finally we have __transactions__ which are a set of operations who are not designed to only commit if they are completed successfully.
+Transactions are not alllowed to fail. 
+If _anything_ fails then everything should be undone and the state should revert to previous state.
+This is useful because if we are, for example, transferring money to another account we want to make sure that the exchange happens seamlessly otherwise we should back out of the operation altogether.
 

cst363/lec/lec10.md

@@ -0,0 +1,43 @@
+# lec10
+
+This lecture has a corresponding lab excercise who's instructions can be found in `triggers-lab.pdf`.
+
+## What is a trigger
+
+Something that executes when _some operation_ is performed
+
+## Structure 
+
+```
+create trigger NAME before some_operation
+when(condition)
+begin
+	do_something
+end;
+```
+
+To explain: First we `create trigger` followed by some trigger name.
+Then we have to denote that this trigger should fire whenever some operation happens.
+This trigger then executes everything in the `begin...end;` section _before_ the new operation happens.
+
+> `after`
+
+Likewise if we want to fire a trigger _after_ some operation we ccan just replace the before keyword with `after`.
+
+> `new.adsf`
+
+Refers to _new_ value being added to a table.
+
+> `old.adsf` 
+
+Refers to _old_ vvalue being changed in a table.
+
+	
+## Trigger Metadata
+
+If you want to look at what triggers exist you can query the `sql_master` table.
+
+```
+select * from sql_master where name='trigger';
+```
+

cst363/lec/lec2.md

@@ -2,61 +2,64 @@
 
 Covering `tables, tuples, data stuff`
 
-## Problem Statement \
+## Problem Statement
+
 We need to be able to manipulate data easily 
 
-> IMS had been using trees for a while a long time ago
+For sometime previous databses systems, like IMS, had been using tree structures for a while but, there was still a demand for a system that _anyone_ could use.
+This issue is what brings us closer to the table structure that we have mentioned in previous lectures.
 
-> Rows --> __atributes__ 
+To actually guide _how_ we use tables we'll use the followig logic:
 
-> Columns --> __tuple__ 
+* Rows --> Contain whole entries or records
+	* all the data in a row is meant to go together
 	
-somtimes we refer to the title of the columns to be fields 
+* Columns --> Individually they are attributes or fields
+	* Each column is guaranteed to have _only_ 1 type of data in it(e.g. name, title, balance, id\_number)
 
-> Table --> __relation__ 
+* Table --> __relation__ 
 
-relational instance as well for another term
+Relational instance as well for another term
 
-> Domain 
-
-The set of values allowed in a field
+* Domain 
+	* The set of values allowed in a field
 
 ## NULL 
 
-cant operate on it at all 
+`NULL` is special, especially in sqlite3 because we aren't allowed to perform operations with it at all.
+If we tried to do for example `NULL < 3` then we would just get back NULL; that way we avoid non-deterministic behavior and we are able to parse out bad results later on.
+There are a few exceptions to NULL however, where they will be accounted for.
 
-> Count
-
-The only thing that lets you operate on NULL. Even then you only get 0 back.
+* Count
+	* We only count if there is a row there or not, the data inside does not matter in this context.
 
 ## Keys Types
 
-> Super Key 
+* Super Key 
+* Candidate Key 
+* Primary Key 
 
-> Candidate Key 
+### Problem Statement 
 
-> Primary Key 
-
-## Problem Statement 
-
-The rows are not distinguishable from each other; we still have a mes of data sitting there unlabeled. Some kind of identifier is necessary to be able to access every tuple in the relational set.
+The rows are not distinguishable from each other; we still have a mess of data sitting there unlabeled. Some kind of identifier is necessary to be able to access every tuple in the relational set.
 
 ### SuperKey 
 
-Set of attr is a superkey for a table as long as that combination of fields remains unique for every tuple in the relational set. 
-In other words if we have multiple fields; f1 f3 f5 might be a good  combo to use as a key into the table.
+A set of attributes is a __superkey__ for a table as long as that combination of fields remains unique for every tuple in the relational set. 
+In other words if we have multiple fields; f1 f3 f5 might be a good  combo to use as a key into the table, because it might be able to identify a unique entry in our table.
 
-> What's a valid superkey? 
+* What's a valid superkey? 
 
 For starters anything that contains another valid superkey 
 Any subset of a full tuple that can uniquely identify any row in the table.
 
-> Can a whole row be a superkey? 
-...full on brainlet.........yes
+* Can a whole row be a superkey? 
+As long as it can identify any unique row in a table then it _is_ a superkey for that table.
 
 ### Candidate Key 
 
 Any super key that wouldn't be a superkey if one of the attr were removed. Say then that we have a super key that takes columns {1,3,5,6,7}, but removing anyone of the rows no longer reliably returns an arbitrary _unique_ row.
+To put it simply it is the most minimal superkey; though this doesn't entail that there can't be multiple candidate keys for a given table.
 
 ### Primary key 
 
@@ -64,5 +67,6 @@ Any candidate key the database designer has chosen to serve as the unique
 
 ### Foreign Key 
 
-Set of attrs in one table that are the primary key attrs of another table. More info about this key type will come later but just know for now that it exists in the wild.
+If a table/relation includes among it's attributes the primary key for another relation then it is referred to as a foreign key because that key references another relation.
+The table being refferred to is identified as a referenced relation.
 

cst363/lec/lec4.md

@@ -1,15 +1,15 @@
 # lec4
 
+This section mostly relies on practicing some of the most basic commands for sqlite3, for that reason most of the content is expressed through practice in the lab sub-section.
 
 ## Lab*
 
-This lecture has some lab questions in the `lab/` dircory named `table1.pdf` *and* some example data called `patients.sql`. 
-`table1.pdf` will have some exercises to learn the basic commands of sqlite and `patients.sql` should have some example data which _table1_ asks you to query.
+This lecture has some lab questions in the `lab/` directory named `table1.pdf` *and* some example data called `patients.sql`. 
+`table1.pdf` will have some exercises to learn the basic commands of sqlite3 and `patients.sql` should have some example data which _table1_ asks you to query.
 
 ## Serverless
 
-Instead of having listen server listen for requests to perform actions upon these requests we simply have some databse held on a machina and we perform all of our sql commands on that machine.
-
-For now we'll be dealing with small test db's so that we can practice the commands and observe each one's behavior; this will give you a good feeling of what does what in sqlite3.
+Instead of having listen server listen for requests to perform actions upon these requests we simply have some database held on our own machine and we perform all of our sql commands on that machine.
+For now we'll be dealing with small test databases so that we can practice the commands and observe each one's behavior; this will give you a good feeling of what does what in sqlite3.
 
 

cst363/lec/lec5.md

@@ -7,33 +7,35 @@ This lecture will have a lab activity in `cst366/lab/1994-census-summary.sql` wi
 
 ## Distinct Values
 
-> Mininum - min(field)
+* Mininum - min(field)
 
 Finds the smallest value in the given filed
 
-> Maximum - max(field)
+* Maximum - max(field)
 
-Find the largest value in th given field
+Find the largest value in the given field
 
 Say we have a column where we know there are duplicate values but we want to konw what the distinct values in the column may be.
 SQLite3 has a function for that: `select distinct field, ... from table;` 
 
-> select substr(field, startIndex, length) ...
+* select substr(field, startIndex, length) ...
 
-_Note_: the start index starts counting at `1` so keep in mind we are offset `+1`.
+_Note_: the start index starts counting at `1` so keep in mind we are offset `+1` compared to other language like C.
 
 ## Joins
 
 Now we want to join to tables together to associate their respective data.
+To accomplish this we can perform a simple `join` to combine tables. 
 Important to note that a simple join does not necessarily take care of duplicate fields.
 If we have duplicate fields we must denote them as `target.field`. 
-Here target is the table with the desired table and field is the desired field.
+Here `target` is the table with the desired table and `field` is the desired field.
 
 ## Type Casting
 
-If we have say `56` we can use a cast to turn it into an integer.
+If we have say `"56"` we can use a cast to turn it into an integer.
 
 > cast(targetString as integer)
 
 This will return with an error if a non number character is given as input to the cast function, here in this example we denote it with `targetString`.
 
+

cst363/lec/lec6.md

@@ -4,7 +4,7 @@
 
 This lecture features a lab activity in the lab/ directory named: `courses-ddl.sql` with instructions in `simple-joins-lab.pdf`.
 
-* Note: Just make sure to read int courses-ddl.sql first then courses-small.sql second otherwise there will be random errors.(I'm not taking responsibility for that garbage so don't flame me)
+* Note: Just make sure to read in courses-ddl.sql _first_ then courses-small.sql _second_ otherwise there will be random errors.(I'm not taking responsibility for that garbage so don't flame me)
 
 ## Natural Joins
 
@@ -15,4 +15,5 @@ Form:
 ```
 select columns_[...] from tableLeft natural join tableRight
 ```
-While ther is no need to write extra `where` statements there is also the issue where there may be accidental matches since attributes are dropped.
+While there is no need to write extra `where` statements there is also the issue where there may be accidental matches since attributes are dropped.
+This implies that if two tables have attributes with the same field name, then only one will be returned in the resulting table.

cst363/lec/lec7.md

@@ -0,0 +1,45 @@
+# lec7
+
+## Lab Activity
+
+This lecture has two correspondnig lab activities in `lab/` using `1994-census-summary.sql` with instrucctions on `aggregation-lab.pdf` and `nested-subqueries-lab.pdf`.
+
+## Null Operations
+
+Take the following table as a trivial example of working data
+
+| a | b |
+|---|---|
+| 1 | 2 |
+| 3 | N |
+
+Where `a` and `b` are attributes and N signifiies a NULL value.
+If we `select a+b from table` we only get back 2 rows like normal but the second row is left empty since we are operating with a NULL value.
+Even if we use multiplication or some kind of comparison against null we simply ignore that row since NULL in sqlite3 doesn't mean 0.
+Instead NULL in sqlite3 actually represents something that doesn't exist.
+
+> count will treat NULL as 0 however
+
+This is the only exception to the _ignore NULL_ "rule".
+
+## Aggregation
+
+This section we'll deal with functions similar to `count average min max`.
+We call these functions _aggreagate_ functions because they aggregate multiple data points into one.
+
+> round(integer)
+
+Rounds off the floating point number to some level of precision.
+
+> group by _attr_
+
+This will group attributes to gether in the result of a query
+
+> having(attribute)
+
+Similar to `where` however we only care about group scope in this case.
+
+## Nested Subqueries
+
+Recall that when we perform a query the result is a table. 
+We can leverage this and perform some query to query a resultant table to further our ability to filter results from a table.

cst363/lec/lec9.md

@@ -0,0 +1,54 @@
+# lec9
+
+## Lab
+
+This lecture has a corresponding lab activity in `lab/`, the instructions are named `views-lab.pdf` and the second one is `contraints-lab.pdf`.
+
+## Views
+
+```
+create view newTabelName as select ... from targetTable;
+```
+
+This will create a `view` which whenever it is queried will pull data from some base table.
+Really the `view` is a kind of "_macro_" which is stored in a `catalog` that normal, non-admin users can use to access a database.
+The catalog is saved in a table somewhere in the database.
+Think of this catalog like a container(_table_) for the other tables in the database.
+
+### Pros & Cons
+
+Problems:
+
+* Computing the view multiple times can be expensive
+* Maintainence
+
+There are two strategies to dealing with the second item: eager and lazy strategies.
+
+1. Eager
+	* If the target table of some view changes the update the view immediately
+2. Lazy
+	* Don't update the view until it is needed(_queried_)
+
+
+## Check Contraint
+
+Checks values when they are inserted to validate their legitimacy.
+
+```
+create table blah(
+	id varchar(8) check (id like "%-%"),
+);
+```
+This is how we can avoid accidently putting in null or downright logically incorrect data into a table.
+
+We can also require entries be unique as well.
+
+```
+create table blah (
+	dept_name varchar(20),
+	...
+	unique(dept_name)
+);
+```
+_KEEP IN MIND HOWEVER_. With `unique()` if we try to check if a new entry is unique it will always fail with NULL since operations with NULL results in false.
+That means we will be able to insert NULL values into the table even if they are not unique.

cst363/readme.md

@@ -1,15 +1,8 @@
-# ?
-Notes are ordered from lec[1].md to lec[N].md 
+# Introduction to Databse Systems & SQLite3
 
-To be stitched later at some point.
-
-## Subheadings 
-
-Each sub heading should represent some topic covered per lecture section. 
-
-> sub-sub headings
-Will be finer details about a particular topic within a lecture.
+Notes are found in `lec/` directory and lab excercises are found in `lab/` directory from this point.
 
 ## Markkdown flavor?
 
-Pandoc, if this compiles nicely on other platforms then great but idfc tbqh famalam
+If you want to compile these lessons to a pdf then use pandoc. 
+Tables are usually the largest source of problems so keep that in mind.