Embedded SQL is a method of combining the computing power of a programming language and the database manipulation capabilities of SQL. Embedded SQL statements are SQL statements written inline with the program source code, of the host language. The embedded SQL statements are parsed by an embedded SQL preprocessor and replaced by host-language calls to a code library. The output from the preprocessor is then compiled by the host compiler. This allows programmers to embed SQL statements in programs written in any number of languages such as C/C++, COBOL and Fortran. This differs from SQL-derived programming languages that don't go through discrete preprocessors, such as PL/SQL and T-SQL.
The SQL standards committee defined the embedded SQL standard in two steps: a formalism called Module Language was defined, then the embedded SQL standard was derived from Module Language. The SQL standard defines embedding of SQL as embedded SQL and the language in which SQL queries are embedded is referred to as the host language. A popular host language is C. Host language C and embedded SQL, for example, is called Pro*C in Oracle and Sybase database management systems, ESQL/C in Informix, and ECPG in the PostgreSQL database management system. SQL may also be embedded in languages like PHP etc.
Systems that support embedded SQL
- APRE is an embedded SQL precompiler provided by Altibase Corp. for its DBMS server.
Microsoft SQL Server
- Embedded SQL for C has been deprecated as of Microsoft SQL Server 2008 although earlier versions of the product support it.
- Embedded SQL for C/C++ is supported on Linux, macOS, OpenVMS and Windows.
- Embedded SQL for COBOL is supported on OpenVMS.
- Embedded SQL for Fortran is supported on OpenVMS.
- Pro*Ada was officially desupported by Oracle in version 7.3. Starting with Oracle8, Pro*Ada was replaced by SQL*Module but appears to have not been updated since. SQL*Module is a module language that offers a different programming method from embedded SQL. SQL*Module supports the Ada83 language standard for Ada.
- Pro*C became Pro*C/C++ with Oracle8. Pro*C/C++ is currently supported as of Oracle Database 11g.
- Pro*COBOL is currently supported as of Oracle Database 11g.
- Pro*FORTRAN is no longer updated as of Oracle8 but Oracle will continue to issue patch releases as bugs are reported and corrected.
- Pro*PL/I was not released with Oracle8. The Pro*PL/I Supplement to the Oracle Precompilers Guide, however, continued to make appearances in the Oracle Documentation Library until release 11g. As of release 12c, the Pro*PL/I has been removed from the Oracle Documentation Library.
- ECPG is part of PostgreSQL since version 6.3.
- Cobol-IT is now distributing a COBOL precompiler for PostgreSQL
- Micro Focus provides support via their OpenESQL preprocessor
Embedded SQL through domain-specific languages
- LINQ-to-SQL embeds a SQL-like language into .NET languages.
- JPA embeds a SQL-like language through Criteria API into Java.
- jOOQ embeds a SQL-like language into Java.
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