description | title | ms.date | f1_keywords | helpviewer_keywords | ms.assetid | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Learn more about: Join Clause (Visual Basic) |
Join Clause |
07/20/2015 |
|
|
6dd37936-b27c-4e00-98ad-154b23f4de64 |
Combines two collections into a single collection. The join operation is based on matching keys and uses the Equals
operator.
Join element In collection _
[ joinClause _ ]
[ groupJoinClause ... _ ]
On key1 Equals key2 [ And key3 Equals key4 [... ]
element
Required. The control variable for the collection being joined.
collection
Required. The collection to combine with the collection identified on the left side of the Join
operator. A Join
clause can be nested in another Join
clause, or in a Group Join
clause.
joinClause
Optional. One or more additional Join
clauses to further refine the query.
groupJoinClause
Optional. One or more additional Group Join
clauses to further refine the query.
key1
Equals
key2
Required. Identifies keys for the collections being joined. You must use the Equals
operator to compare keys from the collections being joined. You can combine join conditions by using the And
operator to identify multiple keys. key1
must be from the collection on the left side of the Join
operator. key2
must be from the collection on the right side of the Join
operator.
The keys used in the join condition can be expressions that include more than one item from the collection. However, each key expression can contain only items from its respective collection.
The Join
clause combines two collections based on matching key values from the collections being joined. The resulting collection can contain any combination of values from the collection identified on the left side of the Join
operator and the collection identified in the Join
clause. The query will return only results for which the condition specified by the Equals
operator is met. This is equivalent to an INNER JOIN
in SQL.
You can use multiple Join
clauses in a query to join two or more collections into a single collection.
You can perform an implicit join to combine collections without the Join
clause. To do this, include multiple In
clauses in your From
clause and specify a Where
clause that identifies the keys that you want to use for the join.
You can use the Group Join
clause to combine collections into a single hierarchical collection. This is like a LEFT OUTER JOIN
in SQL.
The following code example performs an implicit join to combine a list of customers with their orders.
[!code-vbVbSimpleQuerySamples#13]
The following code example joins two collections by using the Join
clause.
[!code-vbVbSimpleQuerySamples#12]
This example will produce output similar to the following:
winlogon (968), Windows Logon
explorer (2424), File Explorer
cmd (5136), Command Window
The following code example joins two collections by using the Join
clause with two key columns.
[!code-vbVbSimpleQuerySamples#17]
The example will produce output similar to the following:
winlogon (968), Windows Logon, Priority = 13
cmd (700), Command Window, Priority = 8
explorer (2424), File Explorer, Priority = 8