rothermal / kappa_sql_pg_solo_challenge

#joins.

##relationships

one to one - for every parent object there is exactly one child object example a countrys only have one capitol

one to many - one parent - many children countrys have multiple citys. or authers have multiple books.

many to many - many parents - many children. see, twins, arnold swartzenager and danny devito. many authors collaborating on many movies.

one to many, foreign key - is an identifier and it usually correspoonds to a primary key in another table.

for example - employees department primary key names dept key ---------------------------> primary key dept key, as foriegn key is = to primary key on other table

foreign key constraints help us normalize our data.

cross join - takes the cross product of both tables cortesion product lots of info.. brings everything back for everyone.. every combination of every row. in both tables. BOOM

inner join - set of rows from both tables that match a specific join predicate. say, select * from employees inner join on department on employees.debtkey = departnet.primary_key.

left outer join - if you have null values in the table you are joining from. so u get all the rows from the the left table

right outer join - if you have null values in the table you are joining to. so you get all the rows from the right table.

full outer join - all null values all values from each table. null or otherwise.