Find the next tag inside a dictionary

Question

I have an XML field inside a SQL Server table, on which I need to know if a couple key/value with a given key and a given value is already used in my table.

So here is my table (simplified).
dbo.mytable :
primaryKey, INT
xml_data, NOT NULL

And the xml_data field is caracterized with the following XSN :

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
    <xsd:element name="a">
        <xsd:complexType>
            <xsd:complexContent>
                <xsd:restriction base="xsd:anyType">
                    <xsd:sequence>
                        <xsd:element name="b" type="NonEmptyString" />
                        <xsd:element name="c" type="NonEmptyString" />
                        <xsd:element name="d" type="NonEmptyString" />
                        <xsd:element name="e" type="xsd:dateTime" />
                        <xsd:element name="dict">
                            <xsd:complexType>
                                <xsd:complexContent>
                                    <xsd:restriction base="xsd:anyType">
                                        <xsd:choice maxOccurs="unbounded">
                                            <xsd:sequence>
                                                <xsd:element name="key" type="NonEmptyString" />
                                                <xsd:element name="value" type="xsd:string" />
                                            </xsd:sequence>
                                        </xsd:choice>
                                    </xsd:restriction>
                                </xsd:complexContent>
                            </xsd:complexType>
                        </xsd:element>
                    </xsd:sequence>
                    <xsd:attribute name="version" type="xsd:float" />
                </xsd:restriction>
            </xsd:complexContent>
        </xsd:complexType>
    </xsd:element>
    <xsd:simpleType name="NonEmptyString">
        <xsd:restriction base="xsd:string">
            <xsd:minLength value="1" />
        </xsd:restriction>
    </xsd:simpleType>
</xsd:schema>

For this given XML (for example) :

<a>
    <b>Value</b>
    <c>Value</c>
    <d>Value</d>
    <e>2017-02-14T00:00:00</e>
    <dict>
        <key>myKey</key>
        <value>myValue</value>
        <key>anotherKey</key>
        <value>myValue</value>
    </dict>
</a>

I need to know if the table contains for the first key "myKey" the value "myValue".

I think I can use the [xml_data].exist() function, but I have issues about how my XQuery should be formed.

I started writing the following XQuery :
for $key in /a/dict/key where data($key) = ''myKey'' return $key
But I can't find out, how to get the following tag.

Which could give "hypotethically" something like :

SELECT [xml_data].exist('
for $key 
in /a/dict/key 
where data($key) = ''myKey'' 
return $key.followingTag == ''myValue''
') FROM dbo.mytable;

References : https://msdn.microsoft.com/en-us/library/ms189869.aspx

Answer 1

Considering the following answer : https://stackoverflow.com/a/19253986/3635715
And the following documentation : https://msdn.microsoft.com/en-us/library/ms178030.aspx

Here is the XQuery for my problem :
data(/a/dict/value[. >> (/a/dict/key[. = "myKey"])[1]])[1]

Here is the answer for my problem :

SELECT COUNT(primaryKey) FROM dbo.mytable
WHERE [xml_data].value('
 data(/a/dict/value[. >> (/a/dict/key[. = "myKey"])[1]])[1]
', 'varchar(max)') = 'myValue'

Be careful this answer only works for first key corresponding to "myKey" found.
Which for me will be the case.

Also considering this Answer : https://stackoverflow.com/a/10408858/3635715
The query can be parameterised this way :

DECLARE @key AS NVARCHAR(max)
DECLARE @value AS NVARCHAR(max)

SET @key = N'myKey'
SET @value = N'myValue'

SELECT COUNT(primaryKey) FROM dbo.mytable
WHERE [xml_data].value('
    data(/a/dict/value[. >> (/a/dict/key[. = sql:variable("@key")])[1]])[1]', 'varchar(max)
    ') = @value