JOIN Clients c ON r.ClientID = c.ClientID Range queries restrict data based on conditions like “the value of Column A must be between X and Y.”Ī good example of this is the query from Exercise 4 of the second lesson: SELECT c.ClientName The queries that can take advantage of indexes typically include conditions that significantly reduce the range of possible values one or more columns can take. Otherwise, it’s more efficient to scan the whole table than to read from an index and jump randomly back and forth to the corresponding table rows. Alternatively, indexes can help when they reduce the number of data blocks accessed to a small fraction of the table size. When indexes are covering indexes, containing all columns from the query-from WHERE conditions, JOIN conditions, and the SELECT list-we avoid reading the corresponding table entirely. We also highlighted two scenarios where the use of indexes in SQL is helpful. We also figured out how to implement queries joining multiple tables and how indexes can speed up such queries.

In the second lesson, we learned the basic structure of B-tree indexes and how to use them to reduce the volume of data we access while executing a query. In the first lesson of SQL Indexes Explained, we learned that SELECT queries are faster when the data is already ordered by values of specific columns.

Sql server indexing