📓 intro to sql

what are relational databases? a collection of tables, where each table represents exactly one type of entity
a table can have multiple columns and multiple rows
each column = an attribute about all entities, each row = information about an entity
what's SQL?
# Structured # Query # Language
notes from http://datacamp.com/tracks/sql-fundamentals
one of the primary usage of SQL is to query databases
## select single column
common queries & keywords
SELECT [column_name] FROM [table_name];
## select all columns (*)
SELECT * FROM [DB_name];
SELECT & FROM are keywords. keywords are not case sensitive but it's good practice to use uppercase
good practices
SELECT DISTINCT [column_1] FROM [DB_name];
SELECT * FROM [DB_name] LIMIT 10;
SELECT COUNT([column_1]) FROM [DB_name];
SELECT COUNT(*) FROM [DB_name];
use '<>' for not equal
you need to specify the column for every condition, so the following is invalid: 'WHERE [column_1] > X AND < Y'

what are relational databases? a collection of tables, where each table represents exactly one type of entity
a table can have multiple columns and multiple rows
each column = an attribute about all entities, each row = information about an entity
what's SQL?
# Structured # Query # Language
notes from http://datacamp.com/tracks/sql-fundamentals
one of the primary usage of SQL is to query databases
## select single column
common queries & keywords
SELECT [column_name] FROM [table_name];
## select all columns (*)
SELECT * FROM [DB_name];
SELECT & FROM are keywords. keywords are not case sensitive but it's good practice to use uppercase
good practices
SELECT DISTINCT [column_1] FROM [DB_name];
SELECT * FROM [DB_name] LIMIT 10;
SELECT COUNT([column_1]) FROM [DB_name];
SELECT COUNT(*) FROM [DB_name];
use '<>' for not equal
you need to specify the column for every condition, so the following is invalid: 'WHERE [column_1] > X AND < Y'