SQL/MX Programming Manual for C and COBOL (G06.24+, H06.03+)

Embedded SQL Statements
HP NonStop SQL/MX Programming Manual for C and COBOL—523627-004
2-13
ANSI Compliance and Portability
•
CONTROL QUERY SHAPE, which forces execution plans by modifying the
operator tree for a prepared statement
•
CONTROL TABLE, which specifies a performance-related option for DML
accesses to a table or view
For the syntax of CONTROL statements, see the SQL/MX Reference Manual.
ANSI Compliance and Portability
If program portability is important, note that CONTROL statements are SQL/MX
extensions to the ANSI standard.
Static and Dynamic CONTROL Statements
CONTROL statement directives influence static SQL statements and dynamic SQL
statements differently. As a programmer, you need to be aware of these differences to
minimize confusion regarding the scope and influence of CONTROL statements in
your program.
CONTROL, Line Order Scope, and Static SQL programs
In an embedded static SQL program, CONTROL statements are preceded by the
preprocessor EXEC SQL directive. In this type of program, a CONTROL statement
directive applies only to static SQL statements. Moreover, CONTROL statements apply
to all statements that follow the CONTROL statement until superseded by another
EXEC SQL CONTROL statement. This type of scope is commonly referred to as line
order scope and applies exclusively to static SQL statements.
CONTROL, Flow Control Scope, and Dynamic SQL programs
In a dynamic SQL program, CONTROL statements are executed dynamically. In
MXCI, for example, you enter CONTROL statements in the same manner as other
SQL statements. You can execute CONTROL statements in a C or COBOL program
with either PREPARE/EXECUTE or EXECUTE IMMEDIATE. In this type of a program,
the scope is such that dynamically executed CONTROL statements apply only to
dynamic SQL statements that are executed after the CONTROL statement has been
executed. This type of scope is called flow control scope and applies exclusively to
dynamic SQL statements. Example 2-1 on page 2-14 illustrates the different types of
Note. Scoping rules behave differently for NonStop SQL/MP than for NonStop SQL/MX. Static
statements are in pure listing order in NonStop SQL/MX. The scope is reset at each procedure
boundary in NonStop SQL/MP. For more information about the differences between NonStop
SQL/MP and NonStop SQL/MX, see the SQL/MX Comparison Guide for SQL/MP Users.