The EXISTS operator is used to test for the existence of any record in a subquery.
The EXISTS operator returns TRUE if the subquery returns one or more records.
SELECT column_name(s) FROM table_name WHERE EXISTS (SELECT column_name FROM table_name WHERE condition);
The HAVING clause was added to SQL because the WHERE keyword cannot be used with aggregate functions.
SELECT column_name(s) FROM table_name WHERE condition GROUP BY column_name(s) HAVING condition ORDER BY column_name(s);
The GROUP BY statement groups rows that have the same values into summary rows, like “find the number of customers in each country”.
The GROUP BY statement is often used with aggregate functions (COUNT(), MAX(), MIN(), SUM(), AVG()) to group the result-set by one or more columns. Continue reading MySQL GROUP BY Statement
The UNION operator is used to combine the result-set of two or more SELECT statements.
SELECT statement within UNION must have the same number of columnsSELECT statement must also be in the same orderA self join is a regular join, but the table is joined with itself.
SELECT column_name(s) FROM table1 T1, table1 T2 WHERE condition;
T1 and T2 are different table aliases for the same table. Continue reading MySQL Self Join
The CROSS JOIN keyword returns all records from both tables (table1 and table2).
The RIGHT JOIN keyword returns all records from the right table (table2), and the matching records (if any) from the left table (table1).
The LEFT JOIN keyword returns all records from the left table (table1), and the matching records (if any) from the right table (table2).
The INNER JOIN keyword selects records that have matching values in both tables. Continue reading MySQL INNER JOIN Keyword
A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Let’s look at a selection from the “Orders” table: Continue reading MySQL Joins