#SQL
- What is having in sql?
- What are the possible issues with indexes?
- Sql works very slowly, what are the possible improvements (the database is MySQL, for example)?
- NoSQL vs SQL Databases
- OLAP vs OLTP Databases
- 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.
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.
- Index All Columns Used in 'where', 'order by', and 'group by' Clauses
- Optimize Like Statements With Union Clause
- Avoid Like Expressions With Leading Wildcards
- Take Advantage of MySQL Full-Text Searches
- Optimize Your Database Schema
- MySQL Query Caching