A query optimizer may receive a query (e.g., from a source that generated the query). Input that specifies both a query hint string and a hint may be received to a hint specification interface. The hint may be applied to the query, from outside the query, to optimize a query execution plan. Applying the hint may be based, at least in part, on a query hint string. For example, which query block is associated with the query hint string may be determined. Upon such a determination, the hint may be applied to the determined query block.