Introduction
Recently I have answered one of the Code Project questions, in brief the question was, how to split the delimited string and return as row values. This is one of the common questions we all are facing in our development. Not only splitting the delimited string, but also we struggle when creating the delimited strings using SQL.
In this article, I will show you how easily this can be done by using the SQL XQuery.
Using the code
Creating delimited strings
Suppose we have a table called DeveloperProject
to store the individual developer project list.
DECLARE @DeveloperProject Table(
DeveoperID INT,
ProjectCode VARCHAR(20)
)
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(1,'CODE_PROJECT')
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(1,'MSFT')
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(1,'REPT_MOD')
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(2,'MSFT')
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(2,'CODE_PROJECT')
INSERT INTO @DeveloperProject(DeveoperID, ProjectCode) VALUES(3,'REPT_MOD')
Now we need to convert this as follows
DeveoperID ProjectCodes
----------- ------------------------
1 CODE_PROJECT,MSFT,REPT_MOD
2 MSFT,CODE_PROJECT
3 REPT_MOD
There are many ways to do this. But here is the easiest way.
SELECT DeveoperID,
REPLACE((SELECT ProjectCode AS'data()'
FROM @DeveloperProject dp2
WHERE dp2.DeveoperID = dp1.DeveoperID
FOR XML PATH('')),' ',',')AS ProjectCodes
FROM @DeveloperProject dp1
GROUP BY DeveoperID
Instead of REPLACE
function you can also use the SUBSTRING
function as below
SELECT DeveoperID,
SUBSTRING((SELECT ','+ ProjectCode
FROM @DeveloperProject dp2
WHERE dp2.DeveoperID = dp1.DeveoperID
FOR XML PATH('')), 2, 8000)AS ProjectCodes
FROM @DeveloperProject dp1
GROUP BY DeveoperID
FOR XML() clause
If you want to get the value of an attribute, rather than the attribute node itself, we can use the data() method.
For ex: if you execute the following query, you will get the xml
output with <ProjectCode>
attribute nodes.
SELECT ProjectCode
FROM @DeveloperProject c2
FOR XML PATH('')
Now run it as follows, and see the result set. It gives the output without <ProjectCode>
nodes.
SELECT ProjectCode AS 'data()'
FROM @DeveloperProject c2
FOR XML PATH('')
Splitting delimited string
Suppose we have a table called DeveloperProjectCSV
to store the developer id and comma separated project list
DECLARE @DeveloperProjectCSV Table(
DeveoperID INT,
ProjectCodes VARCHAR(MAX)
)
We can use previously created script to insert the data to this table.
INSERT INTO @DeveloperProjectCSV(DeveoperID,ProjectCodes)
SELECT DeveoperID,
REPLACE((SELECT
ProjectCode AS 'data()'
FROM @DeveloperProject dp2
WHERE dp2.DeveoperID = dp1.DeveoperID
FOR XML PATH('')), ' ', ',') AS ProjectCodes
FROM @DeveloperProject dp1
GROUP BY DeveoperID
Now the table contains following data
DeveoperID ProjectCodes
----------- ------------------------------
1 CODE_PROJECT,MSFT,REPT_MOD
2 MSFT,CODE_PROJECT
3 REPT_MOD
And we need to split the project codes for each developer.
;WITH cte AS (
SELECT
DeveoperID,
CAST('<r>' + REPLACE(ProjectCodes, ',', '</r><r>') + '</r>' AS XML) AS ProjectCodes
FROM @DeveloperProjectCSV
)
SELECT
DeveoperID,
xTable.xColumn.value('.', 'VARCHAR(MAX)') AS ProjectCode
FROM cte
CROSS APPLY ProjectCodes.nodes('//r') AS xTable(xColumn)
WITH (common_table_expression)
WITH is used to specify the temporary named result set. In above WITH block creates temporary results set with two columns. One is a DeveloperID
and other one is an xml
type column for ProjectCodes
http://msdn.microsoft.com/en-us/library/ms175972.aspx
nodes() Method
The nodes() method is useful when you want to share an xml data type instance into relational data. It allows you to identify nodes that will be mapped into a new row.
nodes (XQuery) as Table(Column)
XQuery
Is a string literal, an XQuery expression. If the query expression constructs nodes, these constructed nodes are exposed in the resulting rowset. If the query expression results in an empty sequence, the rowset will be empty. If the query expression statically results in a sequence that contains atomic values instead of nodes, a static error is raised.
Table(Column)
Is the table name and the column name for the resulting rowset.
http://msdn.microsoft.com/en-us/library/ms188282(v=sql.100).aspx
CROSS APPLY
CROSS APPLY is just like an inner join query clause which allows joining between two table expressions.
http://technet.microsoft.com/en-us/library/ms175156.aspx
Creating delimited strings with SQL 2000
Since SQL 2000 doesn’t support XML PATH
, above query doesn’t work with SQL 2000. As an alternative option we can use COALESCE
or ISNULL
function and create User Defined Function to get the concatenation output.
Suppose we have a table called “DeveloperProject
” with following data inserted.
DeveloperID ProjectCode
----------- --------------------
1 CODE_PROJECT
1 MSFT
1 REPT_MOD
2 MSFT
2 CODE_PROJECT
3 REPT_MOD
First we have to create the concatenation function
CREATE FUNCTION dbo.rowToCSV(@DeveoperID int )
RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE @ProjectCodes VARCHAR(MAX)
SELECT @ProjectCodes = COALESCE(@ProjectCodes + ', ', '') + ProjectCode
FROM DeveloperProject
WHERE DeveoperID = @DeveoperID
RETURN @ProjectCodes
END
By using the above function, you will can get the same output.
SELECT
DeveoperID,
ProjectCodes = dbo.rowToCSV(DeveoperID )
FROM DeveloperProject
GROUP BY DeveoperID
COALESCE and ISNULL
COALESCE
returns the first nonnull expression among its arguments. This is just like ISNULL
function in SQL. Both ISNULL
and COALESCE
can be used to get the same results but there are some differences. http://msdn.microsoft.com/en-us/library/ms190349(v=sql.90).aspx
Splitting delimited string with SQL 2000
Again, SQL 2000 doesn't support WITH
(Common table expression) and the APPLY operators. As an alternative option we can use the spt_values
master table.
SELECT a.DeveloperID,
SUBSTRING(',' + a.ProjectCodes + ',', n.Number + 1, CHARINDEX(',', ',' + a.ProjectCodes + ',', n.Number + 1) - n.Number - 1) AS [Value]
FROM DeveloperProjects AS a
INNER JOIN master..spt_values AS n ON SUBSTRING(',' + a.ProjectCodes + ',', n.Number, 1) = ','
WHERE n.Type = 'p'
AND n.Number > 0
AND n.Number < LEN(',' + a.ProjectCodes + ',')
spt_values
spt_values is an undocumented system table, which contains various data items used by Microsoft written stored procedures. We can use the rows with type = 'P' to have a numbers table with the numbers from 1-2047.