Optimize sql statement

• Create an index on very large tables (>1.000.000) rows
• Use EXIST() instead of COUNT() to find an element in the table
• SELECT fields instead of using SELECT *
• Avoid Subqueries in WHERE Clause
• Avoid SELECT DISTINCT where possible
• Use WHERE Clause instead of HAVING
• Create joins with INNER JOIN (not WHERE)
• Use LIMIT to sample query results
• Use UNION ALL instead of UNION wherever possible
• Use UNION where instead of WHERE ... or ... query.
• Run your query during off-peak hours
• Avoid using OR in join queries
• Choose GROUP BY over window functions
• Use derived and temporary tables
• Drop the index before loading bulk data
• Use materialized views instead of views
• Avoid != or <> (not equal) operator
• Minimize the number of subqueries
• Try to use INNER join as little as possible when you can get the same output using LEFT/RIGHT join.