Database / Google Spanner Database Interview questions
What is a secondary index in Spanner?
A secondary index is an additional sorted structure on one or more non-primary-key columns, created so queries filtering or sorting on those columns don't have to scan the base table.
CREATE INDEX OrdersByDate ON Orders(OrderDate);
By default, a secondary index is stored separately from the base table and only contains the indexed columns plus the primary key. Adding STORING(column) lets you include extra columns directly in the index so a query can be satisfied without a lookup back to the base table, at the cost of extra storage. Indexes can also be declared UNIQUE, and NULL_FILTERED indexes exclude rows where the indexed column is null, which keeps sparse indexes smaller.
What does adding STORING(column) to an index do?
What does a NULL_FILTERED index do?
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