Joins

Front 1

Define alias and the format

Back 1

Used for simplifying the column and table name. Alias can be anything like the first character of the name or its short form etc.

Format:
Select column_name as column alias
From table name as table alias

Front 2

Define the primary key in join function

Back 2

Primary key refers to the unique values for each row like employee ID, product ID etc.

Front 3

How to join two tables?

Back 3

To join two tables, at least one table must have the primary key which must also appear in another table that we want to join together

Front 4

How to select name from employee table and product from product table by joing two tables together?

Back 4

Select employee.name, product.product
From employee, product
Where employee.ID = product.ID

Front 5

How to use inner join to select name from employee table and product from product table?

Back 5

Select employee.name, product.product
From employee inner join product
On employee.ID = product.ID

Front 6

What is the difference between inner join, left join, and right join?

Back 6

Inner join - only show the rows which primary key match another row in another table

Left join - will show all the rows of the first table even though the primary key doesn't match the row with another table

Right join - show all the rows of the second table even though their primary key do not match with the row of another table

Front 7

Define union function

Back 7

Union is used to select the data from two tables.

But it will include all data into one column which you firstly specify at the select statement.

And it only select the unique value; it will not repeat the data twice if it appears more than once at the table.

Front 8

Define union all

Back 8

Same as union but it will select all values including the repeated ones.

Front 9

Union format

Back 9

Select column name from table 1 name
Union
Select column name from table 2 name