how to use concat, like and subconsultas with where?

The objective is that the source table that has two columns, group by column 1 and that a new column indicate separated by commas what column 1 has in column 2 (of origin).

columna 1 - 1 1 2 2 3 3 4 4 columna 2 - a b c a d a f g

and in a new column or table 1 - a b / 2 - b

is something like that

SELECT Main.SubjectID, LEFT(Main.Students,Len(Main.Students)-1) As "Students" FROM ( SELECT DISTINCT ST2.SubjectID, ( SELECT ST1.StudentName + ',' AS [text()] FROM dbo.Students ST1 WHERE ST1.SubjectID = ST2.SubjectID ORDER BY ST1.SubjectID FOR XML PATH (''), TYPE ).value('text()[1]','nvarchar(max)') [Students] FROM dbo.Students ST2 ) [Main]

but is my first time use heidisql and i dont`t know , only i worked with postgresql

and i dont know how to use substring and others

Basic example for using SUBSTRING in MySQL and MariaDB:

SELECT SUBSTRING(`name`, 3) FROM acl_role;

What's the server type to which you connect in HeidiSQL? Microsoft SQL Server probably?

THANKS YOU !!

I'm using heidisql

microsoft sql server i think

Yes, that looks like MS SQL.

You can use the completion proposal to help finding the right syntax for various functions. Just type some chars and press Ctrl + Space:

Thanks !!

and functions that do what "left or len" do

SELECT Main.SubjectID, LEFT(Main.Students,Len(Main.Students)-1) As "Students" FROM maiin

AND OTHER THING, HOW ARE SUBQUERIES NAMED? WITH AS? AND HOW ARE THEY USED?

BECAUSE THIS NOT ?

SELECT asset_tag.asset_id , LEFT(asset_tag, LENGTH(asset_tag.tag_id)-1 AS etiqueta FROM ( SELECT ST2.asset_tag ( SELECT ST1.asset_tag + ',' AS [etiqueta(1)] FROM asset_tag ST1 WHERE asset_tag.tag_id = ST2.asset_tag.tag_id ORDER BY ST1.asset_tag.tag_id FOR XML PATH (''), TYPE

)value('etiqueta()[1]','nvarchar(max)') [asset_tag] ) from asset_tag ST2 )asset_tag ;

i want taht the group "6" have "5,1" , el "1" have "1,3,5" , what i`m doing wrong?

Ok, then you should not group by tag_id. Remove the tag_id from the GROUP BY clause, and replace that concat_ws(...) by just asset_tag.tag_id:

SELECT asset_tag.asset_id, asset_tag.tag_id
FROM public.asset_tag
JOIN ...
WHERE ...
GROUP BY asset_tag.asset_id;

Yes , that error i see but this