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Amelio Vazquez-Reina's questions

Martin Hope
Amelio Vazquez-Reina
Asked: 2014-02-08 10:55:35 +0800 CST
  • 1

假设我运行以下命令：

\d mtb.big_table

我得到如下所示的输出。我的问题是：

  1. 什么是列修饰符？（什么default now()意思？）
  2. 下Indexes，为什么有些索引会引用多个列？（我以为columns只能指一个column）
  3. Foreign-key constraintswhen it talks aboutREFERENCES和下面的下一组 says之间有什么关系"Referenced by"？（为什么只有两个Foreign-key constraintsTABLE 引用？）。

例如，以下条目：

TABLE "dt.table_segment_hierarchy" CONSTRAINT "dx_segment_hierarchy_ancestor_segment_uid_fkey" FOREIGN KEY (ancestor_segment_uid) REFERENCES dt.table_segment(object_uid)

阅读：

TABLE <table_1> CONSTRAINT <column_1> FOREIGN_KEY (<column_2>) REFERENCES <table_2>(<column_3>)

这些表和列之间的关系是什么？

更一般地说，我在哪里可以找到有关\d命令输出格式的更多信息？

                                                   Table "dt.table_segment"
         Column         |            Type             |                              Modifiers                              
------------------------+-----------------------------+---------------------------------------------------------------------
 segment_id             | integer                     | not null default nextval('dt.table_segment2_segment_id_seq'::regclass)
 segment_type           | character varying(31)       | not null
 object_uid             | character varying(255)      | not null
 object_version         | timestamp without time zone | default now()
 name                   | character varying(255)      | not null
 is_active              | boolean                     | not null
 expiration             | integer                     | 
 expiration_unit        | character varying(255)      | 
 frequency_count        | integer                     | 
 matching_expression    | character varying(32672)    | 
 data_vendor_uid        | character varying(255)      | not null
 creation_date          | timestamp without time zone | not null default now()
 researcher_uid         | character varying           | 
 sharing_enabled        | boolean                     | not null default false
 compressed_id          | integer                     | 
Indexes:
    "dx_segment_pkey" PRIMARY KEY, btree (object_uid)
Foreign-key constraints:
    "dx_segment_researcher_fk" FOREIGN KEY (researcher_uid) REFERENCES dt.table_researcher(object_uid)
    "fkeef87e8854520518" FOREIGN KEY (data_vendor_uid) REFERENCES dt.table_data_vendor(object_uid)
Referenced by:
    TABLE "dt.table_segment_hierarchy" CONSTRAINT "dx_segment_hierarchy_ancestor_segment_uid_fkey" FOREIGN KEY (ancestor_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_hierarchy" CONSTRAINT "dx_segment_hierarchy_descendant_segment_uid_fkey" FOREIGN KEY (descendant_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_shared_organization_segments" CONSTRAINT "dx_shared_organization_segments_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_external_id" CONSTRAINT "fk3f8c6d84c87bfc0" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_group_rate" CONSTRAINT "fk710100c4a72a47f" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_group_rate" CONSTRAINT "fk710100c4b8416291" FOREIGN KEY (group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_action" CONSTRAINT "fk7c000342a72a47f" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_action" CONSTRAINT "fk7c000342b7946789" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_edge" CONSTRAINT "fk9c237d147cc05c6a" FOREIGN KEY (parent_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_segment_edge" CONSTRAINT "fk9c237d14a102ddc" FOREIGN KEY (child_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "dt.table_flight_group" CONSTRAINT "fkbeae4f48b8416291" FOREIGN KEY (group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_assets_load" CONSTRAINT "ls_assets_load_winning_group_uid_fkey" FOREIGN KEY (winning_group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_attributions_load" CONSTRAINT "ls_attributions_load_winning_group_uid_fkey" FOREIGN KEY (winning_group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_group_converters_load" CONSTRAINT "ls_group_converters_load_group_uid_fkey" FOREIGN KEY (group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_group_unique_users_load" CONSTRAINT "ls_group_unique_users_load_group_uid_fkey" FOREIGN KEY (group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_campaign_segment_load" CONSTRAINT "ls_campaign_segment_load_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_creative_exchange_hourly_load" CONSTRAINT "ls_creative_exchange_hourly_load_group_uid_fkey" FOREIGN KEY (group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_impressions_load" CONSTRAINT "ls_impressions_load_winning_group_uid_fkey" FOREIGN KEY (winning_group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_related_segment_load" CONSTRAINT "ls_related_segment_load_related_segment_uid_fkey" FOREIGN KEY (related_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_related_segment_load" CONSTRAINT "ls_related_segment_load_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_segment_load" CONSTRAINT "ls_segment_load_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_top_interest_load_cant_modify" CONSTRAINT "ls_top_interest_load_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_top_interest_load" CONSTRAINT "ls_top_interest_load_segment_uid_fkey1" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_winning_segment_hourly_load" CONSTRAINT "ls_winning_segment_hourly_load_winning_group_uid_fkey" FOREIGN KEY (winning_group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_winning_segment_hourly_load" CONSTRAINT "ls_winning_segment_hourly_load_winning_segment_uid_fkey" FOREIGN KEY (winning_segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_winning_segment_list_segments" CONSTRAINT "ls_winning_segment_list_segments_segment_uid_fkey" FOREIGN KEY (segment_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_winning_segment_aggregate_data" CONSTRAINT "winning_segment_aggregate_group_fk" FOREIGN KEY (winning_group_uid) REFERENCES dt.table_segment(object_uid)
    TABLE "fb.ls_winning_segment_aggregate_data" CONSTRAINT "winning_segment_aggregate_segment_fk" FOREIGN KEY (winning_segment_uid) REFERENCES dt.table_segment(object_uid)
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