Question

I have an XML variable that looks like this:

<code>
<IDs>
    <ID id="1">a</ID>
    <ID id="43">d</ID>
    <ID id="3">b</ID>

</IDs>
</code>

I want to use that in a stored procedure (SQL Server) that will update a table.

My table look like this:

ID INT,
a INT,
b INT,
c INT,
d INT

The statement should increase the letter value associated with the id.

SO it would look like this:

Table Row with ID = 1, update column "a" by increasing the current value by 1.
Table Row with ID = 43 - update column "d" by increasing current value by 1.
Finally Table row with ID= 3 - update column "b" by increasing value by 1.

This is what I have so far – (The second line is where i need the most help.):

Update MyTable
SET @letter = letterVal +1
WHERE ID IN(
SELECT x.v.value('@id','INT')
FROM @xmlIDs.nodes('/IDs/ID') x(v)
)

Answer 1

You would have to do something along the lines of this:

DECLARE @input XML = '<code>
<IDs>
    <ID id="1">a</ID>
    <ID id="43">d</ID>
    <ID id="3">b</ID>

</IDs>
</code>'

;WITH ParsedXML AS
(
SELECT
    ID = C.value('(@id)[1]', 'int'),
    ColumnName = C.value('(.)[1]', 'varchar(10)')
FROM @Input.nodes('/code/IDs/ID') AS T(C)
)
UPDATE MyTable 
SET a = CASE WHEN p.ColumnName = 'a' THEN t.a + 1 ELSE t.a END,
    b = CASE WHEN p.ColumnName = 'b' THEN t.b + 1 ELSE t.b END,
    c = CASE WHEN p.ColumnName = 'c' THEN t.c + 1 ELSE t.c END,
    d = CASE WHEN p.ColumnName = 'd' THEN t.d + 1 ELSE t.d END
FROM MyTable t
INNER JOIN ParsedXml p ON t.ID = p.ID

SELECT * FROM Mytable

This will do it – but it’s really quite ugly. The main problem is: you cannot get the column name as a value from somewhere else, to use it in the UPDATE statement – unless you go the dynamic SQL route, which has its own set of pros and cons and can get rather messy.

If you’re interested in dynamic SQL – The Curse and Blessings of Dynamic SQL by Erland Sommarskog is an absolute must-read – read it before you launch into using dynamic SQL!