INFORMIX
Informix-ESQL/C Programmer's Manual
Chapter 14: Using Dynamic SQL
Home Contents Index Master Index New Book

SQL Statements That Are Not Known at Compile Time

 An SQL statement that is not known at compile time is usually one that the user enters in an interactive application. When you write an interactive database-query application like DB-Access, you do not know in advance which databases, tables, or columns the user wants to access, or what conditions the user might apply in a WHERE clause. If an ESQL/C application interprets and runs SQL statements that the end user enters, this application does not know what type of information is to be stored in host variables until after the user enters the statement at runtime.

For example, if a program contains the following DELETE statement, you know the number of values and the data types that you will receive, based on the affected columns:

You can define host variables whose data types are compatible with the data they receive. However, suppose your program provides a prompt for the user such as:

In this case, you do not know until runtime either the name of the table on which the DELETE will take place or the columns that will be listed in the WHERE clause. Therefore, you cannot declare the necessary host variables.

You can dynamically determine a prepared SQL statement as well as information about the tables and columns it accesses with the DESCRIBE statement and the dynamic-management structures. For more information, see Chapter 15, "Determining SQL Statements."



Informix-ESQL/C Programmer's Manual, version 9.1
Copyright © 1998, Informix Software, Inc. All rights reserved.