A simple condition in the structure of filter group condition is a condition (restriction) imposed on properties of specific features of this type.
Each simple condition can contain not more than 7 parts:
name of spatial property of the feature (for instance, Area, Maximum Distance or Scale), name of a table or a query linked with the present feature type;
name of the source to which the name indicated in the previous part is referred; the following components can be indicated as such sources – Geometry, GDB table, GDB query, and also Table of DB <name> or Query of DB <name>, where <name> points to the external database (see section “External databases”);
field name of a table or a query (if the name of the table or query is indicated in the previous part of the condition) or names of a layer and of a feature type of the argument features (for some spatial properties);
relation which should be satisfied for the value of field or property;
relation variant which clarifies the sense of relations when a table field with multiple link is used or when a feature is compared with features of specified layer or type;
one or two operands-constants if a particular relation requires them.
Each simple condition except the first one should be linked with the previous condition by one of logical operators AND or OR.
A simple condition based on spatial characteristics of features has a definite value, either true or false, for any given feature. And for conditions based on table data about features, the third case is also possible – undefined value of condition. When the system checks the simple condition for some feature in which the name of the linked table or query is specified, it selects records of this table (query) which are linked with the feature and checks the specified relation for the fields of these records. If there are no records linked with the feature in the table (query) then simple condition is considered to be undefined for this feature (except for conditions using relations of record existence or relation variant COUNT described below).
Peculiarities of using query fields are described in chapter 36 “Using table information about features in filters”, subsection “Using queries in filter condition”.
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