Simple guides to table joins and window functions in SQL.

The postgresql joins clause is used to combine recors from two or more tables in a database.A join is a means for combining fields from two tables by using values common to each. There are five types of joins as shown below; 1.The inner join. 2.The cross join. 3.The left outer join. 4.The right outer join. 5.The full outer join. THE INNER JOIN It creates a new result table by combining column values of two tables(A and B) based upon the join-predicate. The query compares each row of table A with each row of table B to find all pairs of rows, which satisfy the join predicate. When the join-predicate is satisfied, column values for each matched pair of rows of table A and table B are combined into a result row. Its the most common type of join. The syntax used to perform this kind of join is as shown below; SELECT A.column1,B.column2 .... FROM A INNER JOIN B The image below shows how an in inner join works. THE CROSS JOIN It matches every row of the first table with every row of the seco