POSTGRESQL vs MYSQL

	POSTGRESQL	MYSQL
ANSI SQL compliance	Closer to ANSI SQL standard	Follows some of the ANSI SQL standards
Performance	Slower	Faster
Sub-selects	Yes	No
Transactions	Yes	Yes, however InnoDB table type must be used
Database replication	Yes	Yes
Foreign key support	Yes	No
Views	Yes	No
Stored procedures	Yes	No
Triggers	Yes	No
Unions	Yes	No
Full joins	Yes	No
Constraints	Yes	No
Windows support	Yes	Yes
Vacuum (cleanup)	Yes	No
ODBC	Yes	Yes
JDBC	Yes	Yes
Different table types	No	Yes

SQL UNION

The UNION operator is used to combine the result-set of two or more SELECT statements.
Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

syntax 1.

SELECT column_name(s) FROM table_name1
UNION
SELECT column_name(s) FROM table_name2


syntax 2.

SELECT column_name(s) FROM table_name1
UNION ALL
SELECT column_name(s) FROM table_name2

SQL Joins

SQL joins are used to query data from two or more tables, based on a relationship between certain columns in these tables.

1.The INNER JOIN keyword return rows when there is at least one match in both tables.

SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2
ON table_name1.column_name=table_name2.column_name

2.The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matches in the right table (table_name2).
 
SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

3.The RIGHT JOIN keyword Return all rows from the right table (table_name2), even if there are no matches in the left table (table_name1).

 SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

4.The FULL JOIN keyword return rows when there is a match in one of the tables.

SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name=table_name2.column_name