Adding Solution for 2253

Author: cM2908

hard/2253. Dynamic Unpivoting of a Table (Hard).sql

@@ -0,0 +1,52 @@
+CREATE OR REPLACE FUNCTION unpivot_products_2253()
+RETURNS TEXT
+LANGUAGE PLPGSQL
+AS
+$$
+DECLARE
+	stores_array TEXT[];
+	query_text TEXT := '';
+	store_name TEXT;
+BEGIN
+	--query to find all the stores columns of the products table except product_id column
+	SELECT ARRAY_AGG(column_name)
+	INTO stores_array
+	FROM information_schema.columns
+	WHERE table_name = 'products_2253' AND column_name <> 'product_id';
+
+	-- prepare query
+	FOREACH store_name IN ARRAY stores_array
+	LOOP
+		query_text := query_text || 'SELECT product_id, ''' || store_name || ''' AS store, "' || store_name ||'" FROM products_2253 WHERE "' || store_name || '" IS NOT NULL';
+		query_text := query_text || ' UNION ';
+	END LOOP;
+	
+	query_text := LEFT(query_text,LENGTH(query_text)-6);
+	query_text := query_text || ' ORDER BY product_id,store;';
+
+	--return the query as text	
+	RETURN query_text;
+END
+$$;
+
+SELECT unpivot_products_2253();
+
+-- output of the function:
+SELECT product_id, 'LC_Store' AS store, "LC_Store" 
+FROM products_2253 
+WHERE "LC_Store" IS NOT NULL 
+UNION 
+SELECT product_id, 'Nozama' AS store, "Nozama" 
+FROM products_2253 
+WHERE "Nozama" IS NOT NULL 
+UNION 
+SELECT product_id, 'Shop' AS store, "Shop" 
+FROM products_2253 
+WHERE "Shop" IS NOT NULL 
+UNION 
+SELECT product_id, 'Souq' AS store, "Souq" 
+FROM products_2253 
+WHERE "Souq" IS NOT NULL  
+ORDER BY product_id,store;
+
+--running this query manually will give us expected results