Hi,
I was reading to day how indexing works. And I was trying some query, for example below one. What the range basically means (cost=0.28..8.30 ? I don’t understand this.
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arup@ror ~/part-time-projects/entrylvl (add_index_to_job_sources)$ rails db
psql (9.5.0)
Type "help" for help.
entrylvl_dev=# \d job_sources; Table "public.job_sources" Column | Type | Modifiers
---------------+-----------------------------+----------------------------------------------------------id | bigint | not null default nextval('job_sources_id_seq'::regclass)job_id | bigint |source | character varying |job_source_id | character varying |created_at | timestamp without time zone | not nullupdated_at | timestamp without time zone | not null
Indexes: "job_sources_pkey" PRIMARY KEY, btree (id) "index_job_sources_on_source_and_job_source_id" UNIQUE, btree (source, job_source_id) "index_job_sources_on_job_id" btree (job_id)
Foreign-key constraints: "fk_rails_f45da00eca" FOREIGN KEY (job_id) REFERENCES jobs(id)
entrylvl_dev=# explain select * from job_sources where job_source_id = 'p_1208b146c9eb8905' AND source = 'indeed'; QUERY PLAN
------------------------------------------------------------------------------------------------------------------Index Scan using index_job_sources_on_source_and_job_source_id on job_sources (cost=0.28..8.30 rows=1 width=58) Index Cond: (((source)::text = 'indeed'::text) AND ((job_source_id)::text = 'p_1208b146c9eb8905'::text))
(2 rows)
entrylvl_dev=#
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Thanks,
Arup