key_estimate — Get an estimate of row count for a given set of
leading index key parts
in table_name varchar ,
in index_name varchar ,
in k1 any ,
Given a table and an index, this function takes a random sample
of the index, with the first key part equal to the third argument,
the second equal to the fourth argument and so on. If only the
table and index are given, the returned value is the approximate
count of the entire index.
Normal cast rules are applied to convert the arguments to the
types of the corresponding key parts. If the cast fails, -1 is
The estimates are typically within 10% of the real count. If
there have been random deletions or inserts leading to uneven page
filling or if index entries are of greatly varying $ length, the
estimates may be less precise.
The name of the table as appears in SYS_KEYS, case
The name of the index as appears in sys_keys, case
The value of the first key part. Any number of arguments, up to
the number of key parts in the index in question may follow.
Key_estimate returns the approximate count of entries in the
index with the specified values in the leading key parts. -1 if
cannot be determined.
¶Example 24.404. Returns
the approximate count of entries in index STR1 where the first key
part is the string '123'.