MySQL查詢PostgreSQL裏不工作在軌3.2.11

我正在使用的軌道MySQL查詢PostgreSQL裏不工作在軌3.2.11

grouped_link_counters = uattachment).link_counters.group("year(created_at), month(created_at)").count("created_at")

下面的查詢，並讓用mysql適配器按照軌道控制檯結果。

UserAttachment Load (0.2ms) SELECT `user_attachments`.* FROM `user_attachments` WHERE `user_attachments`.`id` = 132 LIMIT 1 
    (0.2ms) SELECT COUNT(`link_counters`.`created_at`) AS count_created_at, year(created_at), month(created_at) AS year_created_at_month_created_at FROM `link_counters` WHERE `link_counters`.`user_attachment_id` = 132 GROUP BY year(created_at), month(created_at) 
=> {11=>9, 12=>15, 1=>1, 2=>1}

但是，當我使用PostgreSQL相同的命令拋出以下錯誤： -

SELECT COUNT("link_counters"."created_at") AS count_created_at, year(created_at), month(created_at) AS year_created_at_month_created_at FROM "link_counters" WHERE "link_counters"."user_attachment_id" = 1 GROUP BY year(created_at), month(created_at) 
ActiveRecord::StatementInvalid: PG::Error: ERROR: function year(timestamp without time zone) does not exist 
LINE 1: ...link_counters"."created_at") AS count_created_at, year(creat... 
                  ^
HINT: No function matches the given name and argument types. You might need to add explicit type casts. 
: SELECT COUNT("link_counters"."created_at") AS count_created_at, year(created_at), month(created_at) AS year_created_at_month_created_at FROM "link_counters" WHERE "link_counters"."user_attachment_id" = 1 GROUP BY year(created_at), month(created_at) 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/postgresql_adapter.rb:1153:in `async_exec' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/postgresql_adapter.rb:1153:in `exec_no_cache' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/postgresql_adapter.rb:662:in `block in exec_query' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activesupport-3.2.11/lib/active_support/notifications/instrumenter.rb:20:in `instrument' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/postgresql_adapter.rb:661:in `exec_query' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/postgresql_adapter.rb:1248:in `select' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/abstract/database_statements.rb:18:in `select_all' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/relation/calculations.rb:289:in `execute_grouped_calculation' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/relation/calculations.rb:206:in `perform_calculation' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/relation/calculations.rb:159:in `calculate' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/activerecord-3.2.11/lib/active_record/relation/calculations.rb:58:in `count' 
    from (irb):63 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start' 
    from /home/nishutosh/.rvm/gems/[email protected]/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>' 
    from script/rails:6:in `require' 
    from script/rails:6:in `<main>'1.9.3p194 :064 >

誰能告訴我什麼可以做，以獲得從PostgreSQL同樣的反應。在此先感謝！

來源

2013-02-12 Nishutosh Sharma

閱讀消息：「錯誤：函數年（沒有時區的時間戳）不存在」。這個函數在PostgreSQL中不存在，但你可以自己創建它。 – 2013-02-12 13:25:15

請參閱：http://www.postgresql.org/docs/current/static/functions-datetime.html – 2013-02-12 13:28:17

使用'extract'。更多在這裏：http://stackoverflow.com/questions/4493705/mysql-to-postgresql-how-to-modify-this-sql-query – RAJ 2013-02-12 17:34:31

在PostgreSQL中，我們沒有像YEAR，MONTH等幫助函數。取而代之，您可以在PostgreSQL中使用date_part來獲得與MySQL相同的結果。

E.g.

grouped_link_counters = uattachment.link_counters.group("date_part('year', created_at), date_part('month', created_at)").count("created_at")

來源

2013-02-13 09:48:33 RAJ

我想如果我們要在MySQL中使用這個查詢，那麼這贏得了'工作。我的想法是使用'uattachment.link_counters.find_by_sql（「sql query here」）' 但是，謝謝你的答案。非常感謝，它確實有幫助。 – 2013-02-14 08:01:54

MySQL查詢PostgreSQL裏不工作在軌3.2.11

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