SQL Server 2017

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CREATE TABLE a(I INT);
CREATE TABLE b(I INT);
DECLARE @l NVARCHAR(MAX) = '';

SELECT 
    @l = @l + (CAST(s.object_id AS NVARCHAR(50)) + ' ' + REPLACE(s.name, 'x', 'y') + ', ')
FROM sys.tables s
ORDER BY s.name;

SELECT @l;

(No column name)

901578250 a, 917578307 b,

SELECT STRING_AGG(CONCAT(s.object_id,' ',REPLACE(s.name, 'x', 'y')), ',') WITHIN GROUP(ORDER BY s.name)
FROM sys.tables s

(No column name)

901578250 a,917578307 b