Expression/SQL Properties

Expression and SQL Query tags allow data to be derived from formulas, or through queries. Both tag types are executed each time the tag's scan class executes.

Expression

An expression tag can use all of the features available in the expression language. It can refer to other tags, and use operators and functions to calculate a value for the tag.

See also:

Expressions Overview

SQL Query

The value of a SQL Query tag will be the result of the specified SQL query. The query can be any valid query, but should result in only one value. Note that insert and update queries can be used, and will often result in an integer value, so the tag's data type should be set accordingly. By default the tag will attempt to automatically determine the type of query being executed, but if this detection fails, you may manually override the query type. The distinction of query type is necessary for the system to properly retrieve the results.

Like SQL Query bindings in the Vision module, the queries for tags can refer to other tag values. The values of referenced tags will inserted as literal text in the query before being sent to the database.