问题

I have a table that contains a Xml column:

SELECT * 
FROM Sqm

$\"enter$

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.

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 *\'

回答1:

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

回答2:

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)

回答3:

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:

回答4:

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!

来源：https://stackoverflow.com/questions/19165213/how-to-query-for-xml-values-and-attributes-from-table-in-sql-server

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sql-server