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One major difference between indexes and column statistics is that indexes are permanent objects that are updated when changes to the underlying table occur. Column statistics are not updated.

Included columns don't form part of the key for the index, but they do exist on the index. Essentially the values will be duplicated, so there is a storage overhead, but there is a greater chance that your index will cover (i.e. be selected by the query optimizer for) more queries.

Included columns can be used to create a covering indexes without including all the data into the key columns. This covering index has the advantage that the index contains all the columns that are needed for a query.

Indexes provide faster access to data for operations that return a small portion of a table's rows. In general, you should create an index on a column in any of the following situations: The column is queried frequently. A referential integrity constraint exists on the column.

Don't index every column As such, the more write-heavy a table is, the more carefully you should think about the benefit of adding an index. If you've inherited a database with too many indexes, you can start to understand how much each one is used with the view pg_stat_user_indexes .

In the included columns the storage only happens on the leaf level of the index, contrary to the key column of an index. The key column of an index is stored at all levels. The non-key columns don't have the same limitations as the index key columns in terms of the data type.

Usually index rows contain far fewer columns in them than the table itself (except the clustered index, which is the table). A key is a column or columns that defines the order of an index. For example, on an index ordered by ( LastName, FirstName ), then LastName and FirstName are the keys.

The usefulness of an index depends on the design of its key, which you define at the time that you create the index. An index key is a column, an ordered collection of columns, or an expression on which you define an index.

One major difference between indexes and column statistics is that indexes are permanent objects that are updated when changes to the underlying table occur. Column statistics are not updated.

Included columns don't form part of the key for the index, but they do exist on the index. Essentially the values will be duplicated, so there is a storage overhead, but there is a greater chance that your index will cover (i.e. be selected by the query optimizer for) more queries.

Included columns can be used to create a covering indexes without including all the data into the key columns. This covering index has the advantage that the index contains all the columns that are needed for a query.

Indexes provide faster access to data for operations that return a small portion of a table's rows. In general, you should create an index on a column in any of the following situations: The column is queried frequently. A referential integrity constraint exists on the column.

Don't index every column As such, the more write-heavy a table is, the more carefully you should think about the benefit of adding an index. If you've inherited a database with too many indexes, you can start to understand how much each one is used with the view pg_stat_user_indexes .

In the included columns the storage only happens on the leaf level of the index, contrary to the key column of an index. The key column of an index is stored at all levels. The non-key columns don't have the same limitations as the index key columns in terms of the data type.

Usually index rows contain far fewer columns in them than the table itself (except the clustered index, which is the table). A key is a column or columns that defines the order of an index. For example, on an index ordered by ( LastName, FirstName ), then LastName and FirstName are the keys.

The usefulness of an index depends on the design of its key, which you define at the time that you create the index. An index key is a column, an ordered collection of columns, or an expression on which you define an index.