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Explained Embedded SQL


Embedded SQL is a method of combining the computing power of a programming language and the database manipulation capabilities of SQL. It allows programmers to embed SQL statements in programs written in C/C++, Fortran, COBOL, Pascal, etc.

Embedded SQL statements are SQL statements written within application programming languages and preprocessed by a SQL preprocessor before the application program is compiled. There are two types of embedded SQL: static and dynamic.


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. The mixed C and embedded SQL is called Pro*C in Oracle and Sybase database management systems. Other embedded SQL precompilers are Pro*COBOL, Pro*FORTRAN, Pro*PL/I, Pro*Pascal, and SQL*Module (for Ada).



Embedded SQL is a superset of Sybase's T-SQL or Oracle's PL/SQL that lets you place SQL statements in application programs written in languages such as C and COBOL. Pro*C allows the C programmer to write database access code fast and with less of a learning curve. For people who are familiar with both C and SQL, this is a cakewalk. Its worth noting that there are differences between implementations of Pro*C across different database vendors due tothe differences between database architectures, datatypes, etc.

Each new release of a database may announce certain enhancements or changes to its Embedded SQL pre-compiler. It is best to track changes on this front by referring to the vendor database websites. A Pro*C program is compiled in two steps. First, the Pro*C precompiler recognizes the SQL statements embedded in the program, and replaces them with appropriate calls to the functions in the SQL runtime library. The output is pure C/C++ code with all the pure C/C++ portions intact. Then, a regular C/C++ compiler is used to compile the code and produces the executable.

Pro*C Syntax
SQL

All SQL statements need to start with EXEC SQL and end with a semicolon ";". You can place the SQL statements anywhere within a C/C++ block, with the restriction that the declarative statements do not come after the executable statements.

 As an example :

 { int a; /* ... */ EXEC SQL SELECT salary INTO :a 
FROM Employee WHERE SSN=876543210; /* ... */
 printf("The salary is %d\n", a); /* ... */ 
}

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