SQL/PSM

SQL/PSM (SQL/Persistent Stored Modules) is an ISO standard mainly defining an extension of SQL with a procedural language for use in stored procedures. Initially published in 1996 as an extension of SQL-92 (ISO/IEC 9075-4:1996, a version sometimes called PSM-96 or even SQL-92/PSM^[2]), SQL/PSM was later incorporated into the multi-part SQL:1999 standard, and has been part 4 of that standard since then, most recently in SQL:2023.^[3] The SQL:1999 part 4 covered less than the original PSM-96 because the SQL statements for defining, managing, and invoking routines were actually incorporated into part 2 SQL/Foundation, leaving only the procedural language itself as SQL/PSM.^[4] The SQL/PSM facilities are still optional as far as the SQL standard is concerned; most of them are grouped in Features P001-P008.

SQL/PSM standardizes syntax and semantics for control flow, exception handling (called "condition handling" in SQL/PSM), local variables, assignment of expressions to variables and parameters, and (procedural) use of cursors. It also defines an information schema (metadata) for stored procedures. SQL/PSM is one language in which methods for the SQL:1999 structured types can be defined. The other is Java, via SQL/JRT.

SQL/PSM is derived, seemingly directly, from Oracle's PL/SQL. Oracle developed PL/SQL and released it in 1991, basing the language on the US Department of Defense's Ada programming language. However, Oracle has maintained a distance from the standard in its documentation. IBM's SQL PL (used in DB2) and Mimer SQL's PSM^[5] were the first two products officially implementing SQL/PSM. It is commonly thought that these two languages, and perhaps also MySQL/MariaDB's procedural language, are closest to the SQL/PSM standard. ^{[6] [7]} However, a PostgreSQL addon implements SQL/PSM^{[8][9][10][11]} (alongside its other procedural languages like the PL/SQL-derived plpgsql), although it is not part of the core product.^[12]

RDF functionality in OpenLink Virtuoso was developed entirely through SQL/PSM, combined with custom datatypes (e.g., ANY for handling URI and Literal relation objects), sophisticated indexing, and flexible physical storage choices (column-wise or row-wise).

The following implementations adopt the standard, but they are not 100% compatible to SQL/PSM:

Open source:

• HSQLDB stored procedures and functions^[13]
• MySQL stored procedures^[6]
• MariaDB stored procedures^[7]
• OpenLink Virtuoso SQL Procedures (VSP)^[14]
• PostgreSQL PL/pgSQL

Proprietary:

• Oracle PL/SQL
• Microsoft and Sybase Transact-SQL
• Invantive Procedural SQL^[15]
• Mimer SQL stored procedures ^[16]

• Jim Melton, Understanding SQL's Stored Procedures: A Complete Guide to SQL/PSM, Morgan Kaufmann Publishers, 1998, ISBN 1-55860-461-8