Appendix : Legacy Presto components : Mashables and Mashups : Mashups in EMML : Writing Mashups in EMML : Combining Component Mashable or Mashup Results : <join>
<join>
 
<select>
<join> Examples
This statement defines how the data from disparate variables should be joined. Variable data should have repetitive structures that are related based on some criteria in those structures - the foreign keys that define the relation. Optionally, you can also select specific nodes from the result and modify them to build the resulting document structure.
The <join> statement is comparable to inner joins for databases. Only nodes that have values that match the criteria for all variables are included.
You can obtain outer joins in mashups using XQuery. See Using XQuery for Outer Joins for an example. You can also do self-joins in mashups. See Self-Joins with a Single Dataset for an example.
Note:  
The full <join> syntax from previous releases is no longer supported. This syntax used <joincond> children to define join conditions.
You must define at least one join condition, as shown in Defining Join Conditions. You can also, optionally, select which nodes to include in the joined items, as shown in Selecting Nodes for Joined Items with <select>. See also Valid Join Operators and Defining Multiple Conditions. See also Working Samples for information on sample mashups that use this statement.
Can Contain
( select? )
Allowed In
mashup | catch | else | elseif | for | foreach | if | macro | operation | sequence | try | while
Attributes
Name
Required
Description
outputvariable
yes
The required variable to accept the output of this statement.
joincondition
yes
An XPath 2.0 expression defining the variables to join and one or more conditions to apply to determine how variables are joined.
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