110

I have a table that contains a Xml column:

SELECT * 
FROM Sqm

enter image description here

A sample of the xml data of a row would be:

<Sqm version="1.2">
  <Metrics>
    <Metric id="TransactionCleanupThread.RecordUsedTransactionShift" type="timer" unit="µs" count="1" sum="21490"   average="21490"   minValue="73701"    maxValue="73701"                               >73701</Metric>
    <Metric id="TransactionCleanupThread.RefundOldTrans"             type="timer" unit="µs" count="1" sum="184487"  average="184487"  minValue="632704"   maxValue="632704"                              >632704</Metric>
    <Metric id="Database.CreateConnection_SaveContextUserGUID"       type="timer" unit="µs" count="2" sum="7562"    average="3781"    minValue="12928"    maxValue="13006"    standardDeviation="16"     >12967</Metric>
    <Metric id="Global.CurrentUser"                                  type="timer" unit="µs" count="6" sum="4022464" average="670411"  minValue="15"       maxValue="13794345" standardDeviation="1642047">2299194</Metric>
    <Metric id="Global.CurrentUser_FetchIdentityFromDatabase"        type="timer" unit="µs" count="1" sum="4010057" average="4010057" minValue="13752614" maxValue="13752614"                            >13752614</Metric>
  </Metrics>
</Sqm>

In the case of this data, I would want:

SqmId  id                                                   type   unit  count  sum      minValue  maxValue  standardDeviation  Value
=====  ===================================================  =====  ====  =====  ======   ========  ========  =================  ======
1      TransactionCleanupThread.RecordUsedTransactionShift  timer  µs    1      21490    73701     73701     NULL               73701
1      TransactionCleanupThread.RefundOldTrans              timer  µs    1      184487   632704    632704    NULL               632704
1      Database.CreateConnection_SaveContextUserGUID        timer  µs    2      7562     12928     13006     16                 12967
1      Global.CurrentUser                                   timer  µs    6      4022464  15        13794345  1642047            2299194
1      Global.CurrentUser_FetchIdentityFromDatabase         timer  µs    1      4010057  13752614  13752614  NULL               13752614
2      ...

In the end I'll actually be performing SUM(), MIN(), MAX() aggregation. But for now I'm just trying to query an xml column.

In pseudo-code, I would try something like:

SELECT
    SqmId,
    Data.query('/Sqm/Metrics/Metric/@id') AS id,
    Data.query('/Sqm/Metrics/Metric/@type') AS type,
    Data.query('/Sqm/Metrics/Metric/@unit') AS unit,
    Data.query('/Sqm/Metrics/Metric/@sum') AS sum,
    Data.query('/Sqm/Metrics/Metric/@count') AS count,
    Data.query('/Sqm/Metrics/Metric/@minValue') AS minValue,
    Data.query('/Sqm/Metrics/Metric/@maxValue') AS maxValue,
    Data.query('/Sqm/Metrics/Metric/@standardDeviation') AS standardDeviation,
    Data.query('/Sqm/Metrics/Metric') AS value
FROM Sqm

But that SQL query doesn't work:

Msg 2396, Level 16, State 1, Line 2
XQuery [Sqm.data.query()]: Attribute may not appear outside of an element

I've hunted, and it's amazing how poorly documented, or exampled, Xml querying is. Most resources rather than querying a table, query a variable; which I'm not doing. Most resources only use xml querying for filtering and selection, rather than reading values. Most resources read hard-coded child nodes (by index), rather than actual values.

Related resources that I read

Update: .value rather than .query

I tried randomly using .value, in place of .query:

SELECT
    Sqm.SqmId,
    Data.value('/Sqm/Metrics/Metric/@id', 'varchar(max)') AS id,
    Data.value('/Sqm/Metrics/Metric/@type', 'varchar(max)') AS type,
    Data.value('/Sqm/Metrics/Metric/@unit', 'varchar(max)') AS unit,
    Data.value('/Sqm/Metrics/Metric/@sum', 'varchar(max)') AS sum,
    Data.value('/Sqm/Metrics/Metric/@count', 'varchar(max)') AS count,
    Data.value('/Sqm/Metrics/Metric/@minValue', 'varchar(max)') AS minValue,
    Data.value('/Sqm/Metrics/Metric/@maxValue', 'varchar(max)') AS maxValue,
    Data.value('/Sqm/Metrics/Metric/@standardDeviation', 'varchar(max)') AS standardDeviation,
    Data.value('/Sqm/Metrics/Metric', 'varchar(max)') AS value
FROM Sqm

But that also doesn't work:

Msg 2389, Level 16, State 1, Line 3 XQuery [Sqm.data.value()]:
'value()' requires a singleton (or empty sequence), found operand of type 'xdt:untypedAtomic *'

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4 Answers 4

Reset to default
137

Actually you're close to your goal, you just need to use nodes() method to split your rows and then get values:

select
    s.SqmId,
    m.c.value('@id', 'varchar(max)') as id,
    m.c.value('@type', 'varchar(max)') as type,
    m.c.value('@unit', 'varchar(max)') as unit,
    m.c.value('@sum', 'varchar(max)') as [sum],
    m.c.value('@count', 'varchar(max)') as [count],
    m.c.value('@minValue', 'varchar(max)') as minValue,
    m.c.value('@maxValue', 'varchar(max)') as maxValue,
    m.c.value('.', 'nvarchar(max)') as Value,
    m.c.value('(text())[1]', 'nvarchar(max)') as Value2
from sqm as s
    outer apply s.data.nodes('Sqm/Metrics/Metric') as m(c)

sql fiddle demo

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5 Comments

How do i get the "value" of the node itself? There seems to be no way to select m.* to see the secret, magical, intermediate table it constructed. What's the syntax to query the value of an element? e.g. the value of <Metric>8675309</Metric> is "8675309"
@IanBoyd sorry, missed that, see updated. You can use '.' or text if there could be nested elements
What do the aliases s, m, and c represent in this query?
@IanR.O'Brien m is resultset returned by nodes() function, s is sqm table itself, c is column with data type xml in the resultset returned by nodes() function
This is perfect
16

I've been trying to do something very similar but not using the nodes. However, my xml structure is a little different.

You have it like this:

<Metrics>
    <Metric id="TransactionCleanupThread.RefundOldTrans" type="timer" ...>

If it were like this instead:

<Metrics>
    <Metric>
        <id>TransactionCleanupThread.RefundOldTrans</id>
        <type>timer</type>
        .
        .
        .

Then you could simply use this SQL statement.

SELECT
    Sqm.SqmId,
    Data.value('(/Sqm/Metrics/Metric/id)[1]', 'varchar(max)') as id,
    Data.value('(/Sqm/Metrics/Metric/type)[1]', 'varchar(max)') AS type,
    Data.value('(/Sqm/Metrics/Metric/unit)[1]', 'varchar(max)') AS unit,
    Data.value('(/Sqm/Metrics/Metric/sum)[1]', 'varchar(max)') AS sum,
    Data.value('(/Sqm/Metrics/Metric/count)[1]', 'varchar(max)') AS count,
    Data.value('(/Sqm/Metrics/Metric/minValue)[1]', 'varchar(max)') AS minValue,
    Data.value('(/Sqm/Metrics/Metric/maxValue)[1]', 'varchar(max)') AS maxValue,
    Data.value('(/Sqm/Metrics/Metric/stdDeviation)[1]', 'varchar(max)') AS stdDeviation,
FROM Sqm

To me this is much less confusing than using the outer apply or cross apply.

I hope this helps someone else looking for a simpler solution!

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3 Comments

the code misses the opening brackets. also append /text() after id etc for performance increase
This is the most straighforward. Thanks, worked perfecly.
How do we query a table with an XML type column with this approach? Thank you.
10

use value instead of query (must specify index of node to return in the XQuery as well as passing the sql data type to return as the second parameter):

select
    xt.Id
    , x.m.value( '@id[1]', 'varchar(max)' ) MetricId
from
    XmlTest xt
    cross apply xt.XmlData.nodes( '/Sqm/Metrics/Metric' ) x(m)
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8

I don't understand why some people are suggesting using cross apply or outer apply to convert the xml into a table of values. For me, that just brought back way too much data.

Here's my example of how you'd create an xml object, then turn it into a table.

(I've added spaces in my xml string, just to make it easier to read.)

DECLARE @str nvarchar(2000)

SET @str = ''
SET @str = @str + '<users>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Mike</firstName>'
SET @str = @str + '     <lastName>Gledhill</lastName>'
SET @str = @str + '     <age>31</age>'
SET @str = @str + '  </user>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Mark</firstName>'
SET @str = @str + '     <lastName>Stevens</lastName>'
SET @str = @str + '     <age>42</age>'
SET @str = @str + '  </user>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Sarah</firstName>'
SET @str = @str + '     <lastName>Brown</lastName>'
SET @str = @str + '     <age>23</age>'
SET @str = @str + '  </user>'
SET @str = @str + '</users>'

DECLARE @xml xml
SELECT @xml = CAST(CAST(@str AS VARBINARY(MAX)) AS XML) 

--  Iterate through each of the "users\user" records in our XML
SELECT 
    x.Rec.query('./firstName').value('.', 'nvarchar(2000)') AS 'FirstName',
    x.Rec.query('./lastName').value('.', 'nvarchar(2000)') AS 'LastName',
    x.Rec.query('./age').value('.', 'int') AS 'Age'
FROM @xml.nodes('/users/user') as x(Rec)

And here's the output:

enter image description here

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3 Comments

Curious... why the nested cast to Varbinary(max) prior to the xml cast please?
How do we query a table with an XML type column with this approach? Thank you.
@FMFF this method is actually identical to all the others using cross apply.

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