D. SQL 相容性

    The formal name of the SQL standard is ISO/IEC 9075 “Database Language SQL”. A revised version of the standard is released from time to time; the most recent update appearing in 2011. The 2011 version is referred to as ISO/IEC 9075:2011, or simply as SQL:2011. The versions prior to that were SQL:2008, SQL:2003, SQL:1999, and SQL-92. Each version replaces the previous one, so claims of conformance to earlier versions have no official merit. PostgreSQL development aims for conformance with the latest official version of the standard where such conformance does not contradict traditional features or common sense. Many of the features required by the SQL standard are supported, though sometimes with slightly differing syntax or function. Further moves towards conformance can be expected over time.

    SQL-92 defined three feature sets for conformance: Entry, Intermediate, and Full. Most database management systems claiming SQL standard conformance were conforming at only the Entry level, since the entire set of features in the Intermediate and Full levels was either too voluminous or in conflict with legacy behaviors.

    The standard versions beginning with SQL:2003 are also split into a number of parts. Each is known by a shorthand name. Note that these parts are not consecutively numbered.

    • ISO/IEC 9075-1 Framework (SQL/Framework)
    • ISO/IEC 9075-3 Call Level Interface (SQL/CLI)
    • ISO/IEC 9075-4 Persistent Stored Modules (SQL/PSM)
    • ISO/IEC 9075-10 Object Language Bindings (SQL/OLB)
    • ISO/IEC 9075-11 Information and Definition Schemas (SQL/Schemata)
    • ISO/IEC 9075-14 XML-related specifications (SQL/XML)

    The PostgreSQL core covers parts 1, 2, 9, 11, and 14. Part 3 is covered by the ODBC driver, and part 13 is covered by the PL/Java plug-in, but exact conformance is currently not being verified for these components. There are currently no implementations of parts 4 and 10 for PostgreSQL.

    In the following two sections, we provide a list of those features that PostgreSQL supports, followed by a list of the features defined in SQL:2011 which are not yet supported in PostgreSQL. Both of these lists are approximate: There might be minor details that are nonconforming for a feature that is listed as supported, and large parts of an unsupported feature might in fact be implemented. The main body of the documentation always contains the most accurate information about what does and does not work.

    Note

    Feature codes containing a hyphen are subfeatures. Therefore, if a particular subfeature is not supported, the main feature is listed as unsupported even if some other subfeatures are supported.