In the C language, strings are stored in arrays of characters. Dynamic statements are constructed in C language strings. These statements can then be executed using the PREPARE and EXECUTE statements. These SQL statements cannot reference host variables in the same manner as static statements since the C language variables are not accessible by name when the C program is executing.
To pass information between the statements and the C language variables, a data structure called the SQL Descriptor Area (SQLDA) is used. This structure is set up for you by the SQL preprocessor if you specify a list of host variables on the EXECUTE statement in the USING clause. These variables correspond by position to placeholders in the appropriate positions of the prepared statement.
A placeholder is put in the statement to indicate where host variables are to be accessed. A placeholder is either a question mark (?) or a host variable reference as in static statements (a host variable name preceded by a colon). In the latter case, the host variable name used in the actual text of the statement serves only as a placeholder indicating a reference to the SQL descriptor area.
A host variable used to pass information to the database is called a bind variable.
Discuter à propos de cette page dans DocCommentXchange.
|Copyright © 2013, SAP AG ou société affiliée SAP - SAP Sybase SQL Anywhere 16.0|