Embedded SQL programs require preprocessing by a precompiler. The Embedded SQL 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 tasks as the DB-Library example in the "Call-level Method" section earlier in this chapter:
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 that is entered between EXEC SQL and the semicolon (;) contains Embedded SQL statements.
The Embedded SQL 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 the SQL statements are directly included in the C source code, Embedded SQL programs are usually special-purpose applications. Embedded SQL is well suited for environments where the C programmer is also in control of the database structure. However, Embedded SQL is less flexible in environments where the database structure is changing or is not predictable.