Getting Started with DB2 Express-C

246 Getting Started with DB2 Express-C
The question mark (?) in the statement is known as a parameter marker. Using parameter
markers, the program could prepare the statement only once, and then issue EXECUTE
statements providing the different values for the parameter marker.
In DB2 9.7, DB2 introduced a technology called statement concentrator where all the
statements that are the same except for the field values are automatically lumped together
into one single statement with parameter markers, and then EXECUTE statements are
performed with the different values. The statement concentrator does have the intelligence
to determine when not to lump some statements together; for example, when you
purposely add some clauses to influence the DB2 optimizer.
With respect to performance, Static SQL will normally perform better than dynamic SQL
since the access plan in static SQL is performed at precompile time and not at runtime.
However, for environments where there is a lot of activity such as INSERTs and DELETEs,
the statistics calculated at precompile time may not be up-to-date, and therefore, the
access plan of the static SQL may not be optimal. In this case, dynamic SQL may be a
better choice, assuming a RUNSTATS command is frequently executed to collect current
statistics.
Note:
Many users think embedded SQL is only static. In reality, it can be both, static or dynamic.
14.3.3 CLI and ODBC
Call Level Interface (CLI) was originally developed by the X/Open Company and the SQL
Access Group. It was a specification for a callable SQL interface with the purpose of
developing portable C/C++ applications regardless of the RDBMS vendor. Based on a
preliminary draft of X/Open Call Level Interface, Microsoft developed Open Database
Connectivity (ODBC), and later on, the ISO CLI International Standard accepted most of
the X/Open Call Level Interface specification. DB2 CLI is based on both: ODBC and the
International Standard for SQL/CLI as shown in Figure 14.3.