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Difference between CROSS APPLY and OUTER APPLY of SQL XML

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19 Jul 2012CPOL 45.4K   4   1
The difference between CROSS APPLY and OUTER APPLY of SQL XML

Introduction

The APPLY operator comes in two variants, CROSS APPLY and OUTER APPLY. It is useful for joining two SQL tables or XML expressions. CROSS APPLY is equivalent to an INNER JOIN expression and OUTER APPLY is equivalent to a LEFT OUTER JOIN expression.

Solution

Sample XML

XML
DECLARE @XML XML = 
<span class="str">'<Root>
    <UserInfo Id="1" Name="Name 1">
        <CityInfo Id="2" City="City 1" />
        <CityInfo Id="3" City="City 2" >
            <PrefInfo Id="33" Name="Show Whether" />
        </CityInfo>
    </UserInfo>
    <UserInfo Id="2" Name="Name 2">
        <CityInfo Id="4" City="City 3" />
        <CityInfo Id="5" City="City 4" >
            <PrefInfo Id="33" Name="Show Temprature" />
        </CityInfo>
    </UserInfo>
</Root>'</span>

Cross Apply

Cross apply basically uses inner join of two XML collections

SQL
SELECT
    UserInfo.value('@Id', 'BIGINT') as UserId
    , UserInfo.value('@Name', 'VARCHAR(20)') as UserName
    , CityInfo.value('@Id', 'BIGINT') as CityId
    , CityInfo.value('@City', 'VARCHAR(20)') as CityName
    , PrefInfo.value('@Id', 'BIGINT') as PrefId
    , PrefInfo.value('@Name', 'VARCHAR(20)') as PrefName
FROM @xml.nodes('/Root/UserInfo')e(UserInfo)
    CROSS APPLY UserInfo.nodes('CityInfo')b(CityInfo)
    CROSS APPLY CityInfo.nodes('PrefInfo')c(PrefInfo)

Output

UserId   UserName  CityId  CityName  PrefId   PrefName
-------- --------- ------- --------- -------- ----------------
1        Name 1    3       City 2    33       Show Whether
2        Name 2    5       City 4    33       Show Temprature 

Outer Apply

Outer apply basically uses left outer join of two XML collections

SQL
SELECT
    UserInfo.value('@Id', 'BIGINT') as UserId
    , UserInfo.value('@Name', 'VARCHAR(20)') as UserName
    , CityInfo.value('@Id', 'BIGINT') as CityId
    , CityInfo.value('@City', 'VARCHAR(20)') as CityName
    , PrefInfo.value('@Id', 'BIGINT') as PrefId
    , PrefInfo.value('@Name', 'VARCHAR(20)') as PrefName
FROM @xml.nodes('/Root/UserInfo')e(UserInfo)
    CROSS APPLY UserInfo.nodes('CityInfo')b(CityInfo)
    OUTER APPLY CityInfo.nodes('PrefInfo')c(PrefInfo)

Output

UserId  UserName  CityId  CityName  PrefId  PrefName
------- --------- ------- --------- ------- ----------------
1       Name 1    2       City 1    NULL    NULL
1       Name 1    3       City 2    33      Show Whether
2       Name 2    4       City 3    NULL    NULL
2       Name 2    5       City 4    33      Show Temprature 

Originally posted @ JSD Ideas[^]

This article was originally posted at http://jsdideas.blogspot.com/feeds/posts/default

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

 
GeneralNot Enough Content Pin
Tim Corey16-Jul-12 1:37
professionalTim Corey16-Jul-12 1:37 

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