SQL Keys and Joining Tables

Question 1

What do PRIMARY KEY statements do?

Answer 1

provide a unique identifier for each row in a table

Question 2

What is the basic PRIMARY KEY statement format?

Answer 2

CREATE TABLE table_name(column_name data_type PRIMARY KEY, column_name data_type…);

Question 3

What is a foreign key?

Answer 3

a column that contains the primary key of another database

Question 4

How do you specify a column that belongs to a specific table?

Answer 4

table_name.column_name

Question 5

What do JOIN statements do?

Answer 5

combine two tables

Question 6

What is an inner join?

Answer 6

combines two tables with all common values (i.e., ‘1,2,3,4’ corresponds to ‘1,2,3,4’

Question 7

What is an outer join?

Answer 7

combines two tables with only SOME common values (i.e., ‘1,2,3,4’ joins with ‘1,2,5,6’)

Question 8

What is the basic JOIN statement format?

Answer 8

SELECT * FROM table_name1 JOIN table_name2 ON table_name1.column_name = table_name2.column_name;

Question 9

What is a LEFT or RIGHT join?

Answer 9

combine two tables in an outer join, but place ‘null’ values where items do not match

Question 10

What do AS statements do?

Answer 10

rename a column with an “alias”, which can be useful when joining tables

Question 11

What is the basic AS statement format?

Answer 11

table_name.column_name AS ‘alias’