About SQL Server concatenation strings!

The query results are multiple rows and one column. Now we need to splice these results into a string!

 

Select [values] = stuff (select ',' + coal_id from cbm_well_coalbed_info t for XML Path (''), 1, 1 ,'')

 

It's a bit confusing. I have never touched on such a usage. It's very powerful!

 

1. for XML Path

Convert the query result to XML

A. Select well_id, coal_id from cbm_well_coalbed_info t for XML Path ('liuxm ')

The result is as follows:

<Liuxm>

<Well_id> 8ad882351ede89c6011eecb09b290002 </well_id>

<Coal_id> 8ad882351ec8d47c011ec99e01b6002b </coal_id>

</Liuixm>

 

2. Stuff Function

Deletes a string of the specified length and inserts a group of characters at the specified start point.
Stuff (character_expression, start, length, character_expression)
Character_expression: Operator character,
Start: the start point of deletion and insertion,
Length: delete length,
Character_expression: the character to be inserted.

 

Record it first, and then study again...