4. The computer-implemented method of claim 1 , wherein identifying the missing statistics for a database query comprises: determining that the database query processes a plurality of columns; and responsive to determining that the database query processes a plurality of columns, identifying the statistical information to be a multi-column NDV of the plurality of columns.
4. The computer-implemented method of claim 1 , wherein identifying the missing statistics for a database query comprises: determining that the database query processes a plurality of columns; and responsive to determining that the database query processes a plurality of columns, identifying the statistical information to be a multi-column NDV of the plurality of columns. 7. The computer-implemented method of claim 4 , the database query specifies an equijoin operation based on columns from the plurality of columns.