lec5 for networking - lec5 for (databases + lab)

cst363/lec/lec5.md

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+# lec5
+
+## Lab 
+
+This lecture will have a lab activity in `cst366/lab/1994-census-summary.sql` with instructions found in `single-table-queries-2-lab.pdf`.
+
+
+## Distinct Values
+
+> Mininum - min(field)
+
+Finds the smallest value in the given filed
+
+> Maximum - max(field)
+
+Find the largest value in th 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) ...
+
+_Note_: the start index starts counting at `1` so keep in mind we are offset `+1`.
+
+## Joins
+
+Now we want to join to tables together to associate their respective data.
+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.
+
+## Type Casting
+
+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`.
+