SQLSERVER merges subquery data into one field

Business scenario:
There are two tables, department table and employee table
Department table:
Department code department name
1 A
2 A
3 A
4 B

Employee list:
Employee name Department
Zhang San 1
Li Si 1
Wang Wu 1
Zhao Liu 2

Now we need a department personnel report, which requires the employees of this department to be displayed in one column, such as:
Department code department name belongs to personnel
1 A Zhang San, Li Si, Wang Wu
2 BZhao Liu

Solution:
Through the FOR XML PATH function + STUFF function of SQLSERVER, the queried data is combined and spliced, and placed in the specified field
select STUFF((select ',' + emp.name fromt_employee emp where emp.dept_id = dept.id for xml path('')),1,1,'') as emp_names from t_Department dept

Analysis:

One.

FOR XML PATH ("row name") displays the query result set as XML, and displays the results of multiple rows on the same row

--first line

column 1 content -- first column

column 2 content

……

--The second line

column 1 content -- first column

column 2 content

……

Second,
STUFF(expression,start,length,replacewith)
The STUFF function will string is inserted into another string.It deletes characters of the specified length from the beginning of the first string; then inserts the second string at the beginning of the first string.

1, expression
Expression of character data.expression can be a constant, a variable, or a field of a subquery

2, start
start is used to specify the value of the starting position of deletion and insertion.If the value of start is negative or zero, an empty string is returned.If the length of start is greater than the first expression, an empty string is returned.The type of start can also be bigint.
Note: SQLSERVER starts at 1, and a start value of 1 represents the first character.

3, length
length is used to specify the number of characters to be deleted.If the length value is negative, an empty string is returned.If length is greater than the length of the first character_expression, up to the last character in the last character_expression can be deleted.If length is zero, the insertion occurs at the start position and no characters are deleted.The type of length can also be bigint.

4, replacewith
Replace the character expression.Likewise, it can be a constant, a variable, or a field or binary field.
Replaces expression of length characters starting at start.If replacewith is NULL, characters are removed without inserting anything.

5. Return type
If expression is of character data type, character data is returned.
If expression is of binary data type, binary data is returned.

Note:
If the expression is a subquery statement, you need to add a character to the query result, as shown in the example above, otherwise the execution result will bring out the field name of the query:
name >Zhang San Li Si

This is because: directly query the field, FOR XML PATH will return the field name as the column name by default, after adding ',', the column has no name, then the natural return is, Zhang San, Li Si, ... this, then use the STUFF function to remove the first comma, you can

If there are any mistakes or omissions, please give pointers!

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