Getting Started with DB2 Express-C

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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.
Chapter 14 - Introduction to DB2 Application Development 247 Figure 14.3 - DB2 CLI is based on ODBC and ISO CLI International standard DB2 CLI conforms to ODBC 3.51 and can be used as the ODBC Driver when loaded by an ODBC Driver Manager. Figure 14.4 can help you picture DB2 CLI support for ODBC. Figure 14.4 - DB2 CLI conforms to ODBC 3.51 CLI/ODBC has the following characteristics: • The code is easily portable between several RDBMS vendors • Unlike embedded SQL, there is no need for a precompiler or host variables • It runs dynamic SQL • It is very popular To run a CLI/ODBC application all you need is the DB2 CLI driver. This driver is installed from either of the following clients and drivers which can be downloaded and used for free from www.ibm.com/db2/express: • IBM Data Server Client
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GETTING STARTED WITH DB2 Express-C
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Contents About this book ..........
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Contents 7 6.3 DB2 storage model ..
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Contents 9 13.4.2 Cursor stability
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About this book Notices and tradema
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About this Book 13 A book for the c
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About this Book 15 Foreword Innovat
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1 Chapter 1 - What is DB2 Express-C
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Chapter 1 - What is DB2 Express-C?
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1.8 Moving up to another DB2 editio
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4 Chapter 4 - DB2 Environment The D
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Chapter 4 - DB2 Environment 69 conf
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Chapter 4 - DB2 Environment 73 Tabl
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6 Chapter 6 - DB2 Architecture In t
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8 Chapter 8 - Working with Database
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9 Chapter 9 - Data Movement Utiliti
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Chapter 9 - Data Movement Utilities
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11 Chapter 11 - Backup and Recovery
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Getting Started with DB2 Express-C

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