We can utilize the query of listing foreign key with respective table and fields to generate the alter query for adding constraint. For that we will use the XML and temp table and will generate the list of the alter queries
SELECT TABS.NAME AS [REFTABLE], (SELECT NAME FROM SYS.TABLES AS CTAB WHERE (OBJECT_ID = FK.PARENT_OBJECT_ID)) AS [PARENTTABLE], FK.NAME AS [KEYNAME], AC.NAME AS [COLUMNNAME] INTO #TEMPTABLE FROM SYS.TABLES AS TABS INNER JOIN SYS.FOREIGN_KEYS AS FK ON FK.REFERENCED_OBJECT_ID = TABS.OBJECT_ID INNER JOIN SYS.FOREIGN_KEY_COLUMNS AS FKC ON FK.OBJECT_ID = FKC.CONSTRAINT_OBJECT_ID INNER JOIN SYS.ALL_COLUMNS AS AC ON AC.COLUMN_ID = FKC.PARENT_COLUMN_ID AND AC.OBJECT_ID = FKC.PARENT_OBJECT_ID SELECT 'ALTER TABLE ' + [PARENTTABLE] + ' ADD CONSTRAINT ' + [KEYNAME] + ' FOREIGN KEY (' + REPLACE((SELECT [COLUMNNAME] AS 'data()' FROM #TEMPTABLE AS TT WHERE TT.[KEYNAME] = #TEMPTABLE.[KEYNAME] FOR XML PATH('')),' ',',') + ') REFERENCES (' + REPLACE((SELECT [COLUMNNAME] AS 'data()' FROM #TEMPTABLE AS TT WHERE TT.[KEYNAME] = #TEMPTABLE.[KEYNAME] FOR XML PATH('')),' ',',') + ') ON UPDATE CASCADE ON DELETE CASCADE' FROM #TEMPTABLE GROUP BY [KEYNAME], [PARENTTABLE], [REFTABLE] DROP TABLE #TEMPTABLE