Embedded SQL Method

Embedded SQL for C (ESQL/C) programs require preprocessing by a precompiler. The ESQL/C precompiler converts Embedded SQL statements in the program into function calls that can be accepted by a C compiler. The C compiler can then compile the resulting source code into an executable program.

For example, the following Embedded SQL code does the same task as the DB-Library example in Call-level Method:

main()

{

    EXEC SQL BEGIN DECLARE SECTION;

    char first_name[50];

    char last_name[] = "White";

    EXEC SQL END DECLARE SECTION;

  

    EXEC SQL CONNECT TO my_server.pubs

        USER my_login.my_password;

    EXEC SQL SELECT au_fname INTO :first_name

        from authors where au_lname = :last_name;

    return (0);

}

  

Note that each Embedded SQL statement starts with the introductory expression EXEC SQL. This expression tells the precompiler that the code entered between EXEC SQL and the semicolon (;) contains Embedded SQL statements.

The ESQL/C approach, using programming statements similar to Transact-SQL, is more concise than the call-level method approach and is tightly coupled to the existing database structure. Because SQL statements are directly included in the C source code, ESQL/C programs are usually special-purpose applications. ESQL/C is well-suited for environments where the C programmer is also in control of the database structure. However, ESQL/C is less flexible in environments where the database structure is changing or is not predictable. Generally, ESQL/C is used for porting your existing Embedded SQL application code to SQL Server with minimum modifications.


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