The IQ UNIQUE constraint specifies an estimate of the number of distinct values in a column. You can apply the IQ UNIQUE constraint to any column in a table. This constraint helps optimize loading of indexes.
For example, in the state column of the employee table, you would specify IQ UNIQUE(50) to indicate that there are only 50 possible values (assuming U.S. states only). Each of the possible values can occur many times.
When the MINIMIZE_STORAGE database option is ON, it is equivalent to specifying IQ UNIQUE(255) on all new columns. This option is OFF by default as of Version 12.6.
