How Stuff and 'For Xml Path' work in Sql Server

Question

Table is:

+----+------+
| Id | Name |
+----+------+    
| 1  | aaa  |
| 1  | bbb  |
| 1  | ccc  |
| 1  | ffffd  |
| 1  | eee  |
+----+------+

Answer 1

PATH mode is used in generating XML from a SELECT query

1. SELECT   
       ID,  
       Name  
FROM temp1
FOR XML PATH;  

Ouput:

1
aaa



1
bbb



1
ccc



1
ffffd



1
eee

The Output is element-centric XML where each column value in the resulting rowset is wrapped in an row element. Because the SELECT clause does not specify any aliases for the column names, the child element names generated are the same as the corresponding column names in the SELECT clause.

For each row in the rowset a tag is added.

2.
SELECT   
       ID,  
       Name  
FROM temp1
FOR XML PATH('');

Ouput:
1
aaa
1
bbb
1
ccc
1
ffffd
1
eee

For Step 2: If you specify a zero-length string, the wrapping element is not produced.

3. 

    SELECT   

           Name  
    FROM temp1
    FOR XML PATH('');

    Ouput:
    aaa
    bbb
    ccc
    ffffd
    eee

4. SELECT   
        ',' +Name  
FROM temp1
FOR XML PATH('')

Ouput:
,aaa,bbb,ccc,ffffd,eee

In Step 4 we are concatenating the values.

5. SELECT ID,
    abc = (SELECT   
            ',' +Name  
    FROM temp1
    FOR XML PATH('') )
FROM temp1

Ouput:
1   ,aaa,bbb,ccc,ffffd,eee
1   ,aaa,bbb,ccc,ffffd,eee
1   ,aaa,bbb,ccc,ffffd,eee
1   ,aaa,bbb,ccc,ffffd,eee
1   ,aaa,bbb,ccc,ffffd,eee


6. SELECT ID,
    abc = (SELECT   
            ',' +Name  
    FROM temp1
    FOR XML PATH('') )
FROM temp1 GROUP by iD

Ouput:
ID  abc
1   ,aaa,bbb,ccc,ffffd,eee

In Step 6 we are grouping the date by ID.

STUFF( source_string, start, length, add_string ) Parameters or Arguments source_string The source string to modify. start The position in the source_string to delete length characters and then insert add_string. length The number of characters to delete from source_string. add_string The sequence of characters to insert into the source_string at the start position.

SELECT ID,
    abc = 
    STUFF (
        (SELECT   
                ',' +Name  
        FROM temp1
        FOR XML PATH('')), 1, 1, ''
    )
FROM temp1 GROUP by iD

Output:
-----------------------------------
| Id        | Name                |
|---------------------------------|
| 1         | aaa,bbb,ccc,ffffd,eee |
-----------------------------------