Mastering Crystal Reports 9 [Electronic resources] نسخه متنی

SQL Expression Fields

Structured Query Language has its own set of functions and operators. You cannot pass Crystal Syntax or Basic Syntax functions to a database for processing. Any record selection formulas that reference Crystal Syntax or Basic Syntax formulas will be processed in Crystal and not in the database. Since a database is tuned for performance for large records sets, it is more advantageous to process data at the database level whenever possible. SQL expressions are one of the mechanisms you can use to pass processing off to the database. When a statement is coded completely using SQL, it can be passed directly to the database for processing and the resulting data set returned to Crystal Reports. Figure 4.41 shows the Function Tree and Operator Tree for SQL expressions.

Figure 4.41. The Function Tree and Operator Tree for SQL expressions