Informacion de columna clave insuficiente .

[robsergar]

SELECT stock_add.ST_Cant AS Cantidad,
stock_add.ST_COD2 AS Producto,
stock_add.ST_COD2 AS Codigo,
stock_add.st_codprov AS CodProv,
stock_add.ST_DESCRIP AS Detalle,
stock_add.ST_stk_min AS StkMin,
stock_add.ST_PRECIO AS Precio,
Obras.BD_EMP AS Obra,
stock_add.bd_num AS NumeroObra
FROM Obras RIGHT JOIN stock_add ON Obras.BD_NUM = stock_add.bd_num;