The repository contains notes about parts of SQL that differ the most in PostgreSQL, MySQL, Oracle, SQL Server, and SQLite. Currently there are notes about:

• organization of DBMSs (databases, schemas, users, connecting to DBMS, the SET ROLE statement, referencing database objects, synonyms, tablespaces),
• string, mathematical, and time built-in functions,
• access control,
• triggers (I didn't describe triggers in SQL Server, because their syntax differs significantly from other DBMSs),
• sequences,
• paging the result of a SELECT query,
• query optimization (indexes and query execution plan).

The notes are quite complete. At the same time, they are concise, because I wrote information common for all DBMS, and marked the differences.

Sources of information:

• https://stackoverflow.com/questions/7942520/relationship-between-catalog-schema-user-and-database-instance
• the documentations of PostgreSQL, MySQL, Oracle, and SQL Server

Sources of information:

• syntax and description of the SQL Standard,
• draft of the SQL:2011 Standard - drafts of all parts are linked as "SQL:20nn Working Draft Documents" at http://www.wiscorp.com/SQLStandards.html,
• the documentations of PostgreSQL, MySQL, Oracle, SQL Server, and SQLite - I checked them in November 2020

Sources of information:

• syntax of trigger definition in the SQL Standard and its description,
• PostgreSQL, MySQL, and SQLite documentation about triggers. I already knew how triggers work in Oracle, so I haven't read Oracle documentation.

The triggers-additional-info.md file contains additional notes about DML triggers in PostgreSQL and about system triggers.

Sources of information:

• syntax of sequence definition and its usage in SQL Standard,
• PostgreSQL, MySQL, Oracle, SQL Server, and SQLite documentation about sequences,
• additionally, I read about the alternative of a sequence - an "identity" field generated automatically from an implicit sequence - both in SQL Standard and in PostgreSQL, MySQL, Oracle, SQL Server and SQLite documentation.

Sources of information:

• syntax of OFFSET and FETCH FIRST clauses in SQL Standard,
• PostgreSQL, MySQL, Oracle, SQL Server, and SQLite documentation.

Sources of information:

• syntax in the SQL Standard and its description,
• the tutorials and documentations of PostgreSQL, MySQL, Oracle, and SQL Server,
• Security: Access Rights in SQL slides (they are available also in https://web.archive.org/).

Sources of information:

• Wikipedia articles about indexes and query plans,
• PostgreSQL, MySQL, SQL Server, and SQLite documentation about indexes. I only read the most essential information in the SQL Server documentation. I already knew how indexes work in Oracle, so I haven't read Oracle documentation.
• use-the-index-luke.com/sql/explain-plan and subpages.

The following marking are used in the notes:

• green underscore - syntax or behavior defined by SQL Standard
• orange underscore - differences in RDBMS
• blue underscore - when was a syntax introduced to a RDBMS?
• purple underscore - this information is related to transactions
• P M O S L - each letter means respectively: PostgreSQL, MySQL, Oracle, SQL Server, SQLite; they are used on the left margin or in parentheses: (PMOSL: ...)
• [..] - an option
• {..|..} - a choice (sometimes also: ..|.. if it isn't ambiguous, e.g. [..|..] - an optional choice)
• ∨ - logical "or"
• => - logical implication
• ≡ - equality (used for example for aliases)

All SQL keywords are written in UPPERCASE.

The PDF files were generated from the DOCX files, which are available at the src directory, using Microsoft Word 2016.