Top "Explain" questions

Mysql Order by clause using "FileSort"

I have a table structure like comment_id primary key comment_content comment_author comment_author_url When I fire …

mysql indexing database-performance explain

How to force mysql UPDATE query to use index? How to enable mysql engine to automatically use the index instead of forcing it?

Below is the update query/query plan that is not using the compound index that was created recently. The explain …

mysql explain mysql-cluster

How to understand SQLite `EXPLAIN QUERY PLAN` result?

I have read that joins are better than subqueries. But EXPLAIN QUERY PLAN SELECT Queue.Id, NULL FROM Queue INNER …

sql sqlite explain sql-execution-plan

Mysql - "Select like" not using index

I have been playing around with indexes on MySQL (5.5.24, WinXP), but I can't find the reason of why the server …

mysql indexing explain

what is the equivalent of EXPLAIN form SQLite in SQL Server?

I used an SQLite database and run an EXPLAIN statement before executing the actual query to verify if there was …

sql-server sqlite explain

How to determine what is more effective: DISTINCT or WHERE EXISTS?

For example, I have 3 tables: user, group and permission, and two many2many relationships between them: user_groups and group_…

mysql performance distinct inner-join explain

Postgres 9.6: Parallel query does not take max_parallel_workers_per_gather setting

Postgres 9.6; Centos 6.7 ; 24 cores BigTable1 contains 1,500,000,000 rows; weight 180GB. max_worker_processes = 20 max_parallel_workers_per_gather = 12 1) When running EXPLAIN SELECT …

postgresql parallel-processing explain postgresql-9.6