Indexing only affects WHERE clause?

Question

If I have something like:

CREATE INDEX   idx_myTable_field_x
ON             myTable
USING          btree (field_x);

SELECT COUNT(field_x), field_x FROM myTable GROUP BY field_x ORDER BY field_x;

Imagine myTablearound 500,000 rowsand most of the values field_xare unique.

Since I am not using any suggestion WHERE, will the created index even have any effect in my query?

Change . I ask this question because I do not get the difference between the queries before and after creating the index; They always take about 8 seconds (which, of course, is too much time!). Is this behavior expected?

Answer 1

, , (PostgreSQL )

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EXPLAIN ANALYZE VERBOSE, , (- ) .

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Answer 2

field_x - , , myTable.

EDIT. , , postgresql.

Answer 3

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explain SELECT COUNT(field_x), field_x FROM myTable GROUP BY field_x ORDER BY field_x;

, , , postgres: http://www.postgresql.org/docs/8.4/static/sql-explain.html

: http://wiki.postgresql.org/wiki/Image:Explaining_EXPLAIN.pdf, .