Official Documentation
MySQL
- InnoDB Index Types: https://dev.mysql.com/doc/refman/8.0/en/innodb-index-types.html
- EXPLAIN Output Format: https://dev.mysql.com/doc/refman/8.0/en/explain-output.html
- Optimizer Statistics: https://dev.mysql.com/doc/refman/8.0/en/innodb-persistent-stats.html
- Histogram Statistics: https://dev.mysql.com/doc/refman/8.0/en/histogram-statistics.html
PostgreSQL
- Indexes: https://www.postgresql.org/docs/current/indexes.html
- Index Types (B-Tree, GiST, GIN, BRIN): https://www.postgresql.org/docs/current/indexes-types.html
- Using EXPLAIN: https://www.postgresql.org/docs/current/using-explain.html
- Planner Statistics: https://www.postgresql.org/docs/current/planner-stats.html
SQL Server
- Indexes Overview: https://learn.microsoft.com/en-us/sql/relational-databases/indexes/indexes
- Execution Plans: https://learn.microsoft.com/en-us/sql/relational-databases/performance/execution-plans
- Statistics: https://learn.microsoft.com/en-us/sql/relational-databases/statistics/statistics
Oracle
- Indexes and Index-Organized Tables: https://docs.oracle.com/en/database/oracle/oracle-database/
- DBMS_STATS: https://docs.oracle.com/en/database/oracle/oracle-database/
- SQL Tuning Guide (Execution Plans): https://docs.oracle.com/en/database/oracle/oracle-database/
ANSI SQL
- ISO/IEC 9075 (SQL Standard) — indexing is intentionally out of scope;
the standard defines query semantics only, not physical access paths.