The Context References section describes how context references are used to build the tables on which queries are executed. These tables contain multiple fields that may be referred in different parts of the query, i.e. in the WHERE clause.
Field references may comprise of two or three parts:
1. When a query has just one context reference in the FROM clause, fields in the table that was built from this reference may be referred with a two-part Field References:
contextEntityName$dataTableFieldName
In this Field Reference, contextEntityName is the name of the context variable or function that was used by the single Context Reference in the query. dataTableFieldName is the name of the field in the Table Format of the Data Table containing the value of that entity.
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Example: SELECT userInfo$firstname FROM users.*:userInfo In this example, the Field Reference userInfo$firstname refers to the firstname field of a Data Table containing the value of the userInfo variable in all contexts corresponding to the users.* mask. |
2. If a query has more then one Context Reference, each reference must have an alias so you'd be able to refer to the fields of the table that was built from it. The alias is assigned using the AS keyword:
contextReference AS tableAlias
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Example: users.*:userInfo as ui Here we give a table built from the users.*:userInfo Context Reference an alias named ui. Now we can refer to the fields of this table using the alias. |
The generic form of a Field Reference that includes an alias is:
tableAlias.contextEntityName$dataTableFieldName
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Example: SELECT ui.userInfo$firstname FROM users.*:userInfo as ui This query works exactly as the query from previous example, but here field in the table build from "users.*:userInfo" is referred by an alias. You can see another example of using an alias below, in Example 6. |
Click here to see where Field References may appear in Query Language Syntax.
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At first look it may seem that a reference to a field should include only two components: tableAlias and fieldName. But AggreGate Query Language lets you generate one source table (a table on which the query will be run) from the values of several context variables or from the output of several context functions. That is why we need an additional entityName. It points to the name of a context variable or a function which contains the fieldName field. |
