#SQL

• What is having in sql?
• What are the possible issues with indexes?

• HAVING filters records that work on summarized GROUP BY results.
• HAVING applies to summarized group records, whereas WHERE applies to individual records.
• Only the groups that meet the HAVING criteria will be returned.
• HAVING requires that a GROUP BY clause is present.
• WHERE and HAVING can be in the same query.

• https://www.dofactory.com/sql/having

Although indexes are intended to enhance a database's performance, there are times when they should be avoided.

• The following guidelines indicate when the use of an index should be reconsidered.
• Indexes should not be used on small tables.
• Tables that have frequent, large batch updates or insert operations.
• Indexes should not be used on columns that contain a high number of NULL values.
• Columns that are frequently manipulated should not be indexed.

• https://www.tutorialspoint.com/sql/sql-indexes.htm