1. A computer implemented method, comprising: receiving an instruction that relates to defining an attribute within a body of records of a database wherein the instruction specifies a constraint on an attribute that restricts values in said attribute to non-NULL values and a non-NULL default value for said attribute; in response to receiving said instruction, adding said attribute to said body of records; wherein upon completing processing of said instruction: said attribute holds NULL values for said body of records, and metadata of said database defines: said constraint on said attribute restricting said values in said attribute to said non-NULL values, and said non-NULL default value for said attribute; receiving a query to read said attribute; in response to receiving said query, computing said query, wherein computing said query includes: making a determination that (a) said metadata defines said constraint on said attribute restricting said values in said attribute to said non-NULL values, (b) said metadata defines said non-NULL default value for said attribute, and (c) two or more records of said body of records hold a NULL value for said attribute; returning, as a value for said two or more records, said non-NULL default value defined by said metadata instead of said NULL value; wherein the method is performed by one or more computing devices.