{"id":41226,"date":"2026-03-18T10:58:47","date_gmt":"2026-03-18T10:58:47","guid":{"rendered":"https:\/\/www.railscarma.com\/?p=41226"},"modified":"2026-03-18T10:59:31","modified_gmt":"2026-03-18T10:59:31","slug":"rail-join-%e3%82%a2%e3%82%af%e3%83%86%e3%82%a3%e3%83%96%e3%83%bb%e3%83%ac%e3%82%b3%e3%83%bc%e3%83%89%e3%83%bb%e3%82%af%e3%82%a8%e3%83%aa%e3%83%bb%e3%82%a4%e3%83%b3%e3%82%bf%e3%83%bc%e3%83%95%e3%82%a7","status":"publish","type":"post","link":"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/rail-join-%e3%82%a2%e3%82%af%e3%83%86%e3%82%a3%e3%83%96%e3%83%bb%e3%83%ac%e3%82%b3%e3%83%bc%e3%83%89%e3%83%bb%e3%82%af%e3%82%a8%e3%83%aa%e3%83%bb%e3%82%a4%e3%83%b3%e3%82%bf%e3%83%bc%e3%83%95%e3%82%a7\/","title":{"rendered":"Rails\u306e\u7d50\u5408\uff1aActive Record\u30af\u30a8\u30ea\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30a4\u30b9\u306e\u5b8c\u5168\u30ac\u30a4\u30c9"},"content":{"rendered":"<div data-elementor-type=\"wp-post\" data-elementor-id=\"41226\" class=\"elementor elementor-41226\" data-elementor-post-type=\"post\">\n\t\t\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-718dbb9 elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"718dbb9\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-ac57bcd\" data-id=\"ac57bcd\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-f49ab0d elementor-widget elementor-widget-text-editor\" data-id=\"f49ab0d\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Ruby on Rails\u3067\u4f5c\u696d\u3059\u308b\u3068\u304d\u3001\u958b\u767a\u8005\u304c\u5229\u7528\u3067\u304d\u308b\u6700\u3082\u5f37\u529b\u306a\u6a5f\u80fd\u306e1\u3064\u304cActive Record\u3067\u3059\u3002SQL\u306e\u4ee3\u308f\u308a\u306bRuby\u3092\u4f7f\u3063\u3066\u30af\u30a8\u30ea\u3092\u66f8\u304f\u3053\u3068\u304c\u3067\u304d\u308b\u306e\u3067\u3001\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u3068\u306e\u3084\u308a\u53d6\u308a\u304c\u7c21\u5358\u306b\u306a\u308a\u307e\u3059\u3002\u3057\u304b\u3057\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u304c\u5927\u304d\u304f\u306a\u308b\u306b\u3064\u308c\u3066\u3001\u95a2\u9023\u3059\u308b\u8907\u6570\u306e\u30c6\u30fc\u30d6\u30eb\u304b\u3089\u30c7\u30fc\u30bf\u3092\u53d6\u5f97\u3059\u308b\u5fc5\u8981\u304c\u51fa\u3066\u304f\u308b\u3053\u3068\u304c\u3088\u304f\u3042\u308a\u307e\u3059\u3002\u305d\u3053\u3067 <\/span><b>\u30b8\u30e7\u30a4\u30f3\u30ba<\/b><span style=\"font-weight: 400;\"> \u304c\u767b\u5834\u3059\u308b\u3002.<\/span><\/p><p><span style=\"font-weight: 400;\">\u3053\u306e\u30ac\u30a4\u30c9\u3067\u306f\u3001Rails\u306e\u7d50\u5408\u3092\u8a73\u3057\u304f\u8abf\u3079\u3001Active Record Query Interface\u3067\u306e\u52d5\u4f5c\u3092\u7406\u89e3\u3057\u3001\u5b9f\u969b\u306e\u30b7\u30ca\u30ea\u30aa\u3067\u52b9\u7387\u7684\u306b\u4f7f\u7528\u3059\u308b\u65b9\u6cd5\u3092\u5b66\u3073\u307e\u3059\u3002.<\/span><\/p><h3><strong>Rails\u306eJoins\u3068\u306f\uff1f<\/strong><\/h3><p><span style=\"font-weight: 400;\">\u7d50\u5408\u306f\u3001\u95a2\u9023\u3059\u308b\u30ab\u30e9\u30e0\u306b\u57fa\u3065\u3044\u30662\u3064\u4ee5\u4e0a\u306e\u30c6\u30fc\u30d6\u30eb\u306e\u884c\u3092\u7d50\u5408\u3059\u308b\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u64cd\u4f5c\u3067\u3059\u3002Rails\u3067\u306f\u3001\u7d50\u5408\u306b\u3088\u3063\u3066\u751f\u306eSQL\u3092\u66f8\u304b\u305a\u306b\u95a2\u9023\u3059\u308b\u30ec\u30b3\u30fc\u30c9\u3092\u52b9\u7387\u7684\u306b\u53d6\u5f97\u3067\u304d\u307e\u3059\u3002.<\/span><\/p><p><span style=\"font-weight: 400;\">\u4f8b\u3048\u3070\u30012\u3064\u306e\u30e2\u30c7\u30eb\u3092\u8003\u3048\u3066\u307f\u3088\u3046\uff1a<\/span><\/p><ul><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">\u30e6\u30fc\u30b6\u30fc<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">\u5f79\u8077<\/span><\/li><\/ul><p><span style=\"font-weight: 400;\">\u30e6\u30fc\u30b6\u30fc\u306f\u591a\u304f\u306e\u6295\u7a3f\u3092\u6301\u3061\u3001\u6295\u7a3f\u306f\u30e6\u30fc\u30b6\u30fc\u306b\u5c5e\u3059\u308b\u3002\u6295\u7a3f\u3068\u4e00\u7dd2\u306b\u30e6\u30fc\u30b6\u30fc\u3092\u53d6\u5f97\u3057\u305f\u3044\u5834\u5408\u306f\u3001join\u3092\u4f7f\u3046\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002.<\/span><\/p><h3><strong>Rails\u306e\u7d50\u5408\u306e\u7a2e\u985e<\/strong><\/h3><p><span style=\"font-weight: 400;\">Rails\u306f\u4e3b\u306b\u4ee5\u4e0b\u306e\u30bf\u30a4\u30d7\u306e\u7d50\u5408\u3092\u30b5\u30dd\u30fc\u30c8\u3057\u3066\u3044\u307e\u3059\uff1a<\/span><\/p><h4><strong>1.INNER JOIN (joins)<\/strong><\/h4><p><span style=\"font-weight: 400;\">Rails\u3067\u6700\u3082\u3088\u304f\u4f7f\u308f\u308c\u308b\u7d50\u5408\u306fINNER JOIN\u3067\u3059\u3002.<\/span><\/p><pre><span style=\"font-weight: 400;\">\u30e6\u30fc\u30b6\u30fc<\/span><span style=\"font-weight: 400;\">.\u30b8\u30e7\u30a4\u30f3\u30ba<\/span><span style=\"font-weight: 400;\">(<\/span><b><i>\u6295\u7a3f<\/i><\/b><span style=\"font-weight: 400;\">)<\/span><\/pre><p><span style=\"font-weight: 400;\">\u3053\u306e\u30af\u30a8\u30ea\u306f\u3001\u5c11\u306a\u304f\u3068\u30821\u3064\u306e\u6295\u7a3f\u3092\u6301\u3064\u30e6\u30fc\u30b6\u30fc\u306e\u307f\u3092\u8fd4\u3057\u307e\u3059\u3002.<\/span><\/p><p><strong>SQL\u3068\u540c\u7b49\uff1a<\/strong><\/p><pre><b>\u30bb\u30ec\u30af\u30c8<\/b><span style=\"font-weight: 400;\"> \u30e6\u30fc\u30b6\u30fc.<\/span><span style=\"font-weight: 400;\">*<\/span> <b>\u30d5\u30ed\u30e0<\/b><span style=\"font-weight: 400;\"> \u30e6\u30fc\u30b6\u30fc<\/span>\n<b>\u30a4\u30f3\u30ca\u30fc<\/b> <b>\u30b8\u30e7\u30a4\u30f3<\/b><span style=\"font-weight: 400;\"> \u6295\u7a3f <\/span><b>\u30aa\u30f3<\/b><span style=\"font-weight: 400;\"> posts.user_id <\/span><span style=\"font-weight: 400;\">=<\/span><span style=\"font-weight: 400;\"> \u30e6\u30fc\u30b6\u30fc.<\/span><b>\u30a2\u30a4\u30c9\u30eb<\/b><span style=\"font-weight: 400;\">;<\/span><\/pre><p><strong>\u91cd\u8981\u306a\u30dd\u30a4\u30f3\u30c8<\/strong><\/p><ul><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">\u4e00\u81f4\u3059\u308b\u30ec\u30b3\u30fc\u30c9\u306e\u307f\u3092\u8fd4\u3059<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">\u6295\u7a3f\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u3092\u9664\u5916<\/span><\/li><\/ul><h4><strong>2.LEFT OUTER JOIN (left_joins)<\/strong><\/h4><p><span style=\"font-weight: 400;\">\u6295\u7a3f\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u3082\u542b\u3081\u3066\u3059\u3079\u3066\u306e\u30e6\u30fc\u30b6\u30fc\u306b\u9069\u7528\u3057\u305f\u3044\u5834\u5408\u306f\u3001\u5de6\u7d50\u5408\u3092\u4f7f\u7528\u3057\u307e\u3059\u3002.<\/span><\/p><pre>\u30e6\u30fc\u30b6\u30fc.left_joins(<strong><em>\u6295\u7a3f<\/em><\/strong>)<\/pre><p><strong>SQL\u3068\u540c\u7b49\uff1a<\/strong><\/p><pre><strong>\u30bb\u30ec\u30af\u30c8<\/strong> \u30e6\u30fc\u30b6\u30fc <strong>\u30d5\u30ed\u30e0<\/strong> \u30e6\u30fc\u30b6\u30fc\n<strong>\u5de6<\/strong> <strong>\u5916\u5074<\/strong> <strong>\u30b8\u30e7\u30a4\u30f3<\/strong> \u6295\u7a3f <strong>\u30aa\u30f3<\/strong> posts.user_id = users.<strong>\u30a2\u30a4\u30c9\u30eb<\/strong>;<\/pre><p><strong>\u91cd\u8981\u306a\u30dd\u30a4\u30f3\u30c8<\/strong><\/p><ul><li>\u3059\u3079\u3066\u306e\u30e6\u30fc\u30b6\u30fc\u3092\u542b\u3080<\/li><li>\u6295\u7a3f\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u306e\u6295\u7a3f\u306fNULL\u304b\u3082\u3057\u308c\u306a\u3044<\/li><\/ul><h4><strong>3.\u30a4\u30f3\u30af\u30eb\u30fc\u30c9 vs \u30b8\u30e7\u30a4\u30f3<\/strong><\/h4><p>Rails\u306b\u306f\u30a4\u30fc\u30ac\u30fc\u30ed\u30fc\u30c7\u30a3\u30f3\u30b0\u7528\u306e\u30a4\u30f3\u30af\u30eb\u30fc\u30c9\u304c\u7528\u610f\u3055\u308c\u3066\u3044\u307e\u3059\u304c\u3001\u3053\u308c\u306f\u3057\u3070\u3057\u3070join\u3068\u6df7\u540c\u3055\u308c\u307e\u3059\u3002.<\/p><pre>User.includes()<strong><em>\u6295\u7a3f<\/em><\/strong>)<\/pre><p><strong>\u9055\u3044\u3060\uff1a<\/strong><\/p><ul><li>\u7d50\u5408 \u2192 \u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30ec\u30d9\u30eb\u3067\u30c7\u30fc\u30bf\u3092\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0<\/li><li>\u3092\u542b\u3080 \u2192 N+1\u30af\u30a8\u30ea\u3092\u9632\u3050<\/li><\/ul><h3><strong>\u30b8\u30e7\u30a4\u30f3\u306b\u3088\u308b\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0<\/strong><\/h3><p>\u7d50\u5408\u3068\u6761\u4ef6\u3092\u7d44\u307f\u5408\u308f\u305b\u3066\u7d50\u679c\u3092\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002.<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong>).where(<strong><em>\u6295\u7a3f<\/em><\/strong> { <strong><em>\u3092\u51fa\u7248\u3057\u305f\uff1a<\/em><\/strong> true })<\/pre><p>\u6295\u7a3f\u3092\u516c\u958b\u3057\u305f\u30e6\u30fc\u30b6\u30fc\u3092\u8fd4\u3057\u307e\u3059\u3002.<\/p><h3><strong>\u8907\u6570\u306e\u30a2\u30bd\u30b7\u30a8\u30fc\u30b7\u30e7\u30f3\u306b\u53c2\u52a0\u3059\u308b<\/strong><\/h3><p>Rails\u3067\u306f\u8907\u6570\u306e\u7d50\u5408\u3092\u9023\u7d50\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002.<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong> <strong><em>\u30b3\u30e1\u30f3\u30c8<\/em><\/strong>)<\/pre><p>\u3053\u308c\u306f\u3001\u30e6\u30fc\u30b6\u30fc\u2192\u6295\u7a3f\u2192\u30b3\u30e1\u30f3\u30c8\u3092\u7d50\u5408\u3059\u308b\u3002.<\/p><p><strong>SQL\u3068\u540c\u7b49\uff1a<\/strong><\/p><pre><strong>\u30bb\u30ec\u30af\u30c8<\/strong> \u30e6\u30fc\u30b6\u30fc <strong>\u30d5\u30ed\u30e0<\/strong> \u30e6\u30fc\u30b6\u30fc\n<strong>\u30a4\u30f3\u30ca\u30fc<\/strong> <strong>\u30b8\u30e7\u30a4\u30f3<\/strong> \u6295\u7a3f <strong>\u30aa\u30f3<\/strong> posts.user_id = users.<strong>\u30a2\u30a4\u30c9\u30eb<\/strong>\n<strong>\u30a4\u30f3\u30ca\u30fc<\/strong> <strong>\u30b8\u30e7\u30a4\u30f3<\/strong> \u30b3\u30e1\u30f3\u30c8 <strong>\u30aa\u30f3<\/strong> comments.post_id = posts.<strong>\u30a2\u30a4\u30c9\u30eb<\/strong>;<\/pre><h3><strong>\u7279\u5b9a\u306e\u5217\u3092\u9078\u629e\u3059\u308b<\/strong><\/h3><p>\u30c7\u30d5\u30a9\u30eb\u30c8\u3067\u306f\u3001\u7d50\u5408\u306f\u30d9\u30fc\u30b9\u30c6\u30fc\u30d6\u30eb\u306e\u3059\u3079\u3066\u306e\u30ab\u30e9\u30e0\u3092\u8fd4\u3057\u307e\u3059\u3002.<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong>).select(\"users.name, posts.title\")<\/pre><p><strong>\u30d2\u30f3\u30c8<\/strong><\/p><p>\u30bb\u30ec\u30af\u30c8\u3092\u4f7f\u7528\u3057\u3066\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u6700\u9069\u5316\u3057\u3001\u30e1\u30e2\u30ea\u4f7f\u7528\u91cf\u3092\u524a\u6e1b\u3059\u308b\u3002.<\/p><h3><strong>Distinct\u3092Join\u3067\u4f7f\u7528\u3059\u308b<\/strong><\/h3><p>\u7d50\u5408\u306f\u91cd\u8907\u3057\u305f\u30ec\u30b3\u30fc\u30c9\u3092\u8fd4\u3059\u3053\u3068\u304c\u3042\u308b\u3002.<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong>).distinct<\/pre><p>\u3053\u308c\u306b\u3088\u308a\u3001\u30e6\u30cb\u30fc\u30af\u306a\u30e6\u30fc\u30b6\u30fc\u3092\u78ba\u5b9f\u306b\u8fd4\u3059\u3053\u3068\u304c\u3067\u304d\u308b\u3002.<\/p><h3><strong>\u30b0\u30eb\u30fc\u30d7\u3068\u30ab\u30a6\u30f3\u30c8\u306e\u4f7f\u7528<\/strong><\/h3><p>\u7d50\u5408\u3092\u4f7f\u7528\u3057\u3066\u30c7\u30fc\u30bf\u3092\u96c6\u7d04\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002.<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong>).group(\"users.id\").count<\/pre><p><strong>\u51fa\u529b\u4f8b\uff1a<br \/><\/strong>{1 =&gt; 5, 2 =&gt; 3}<\/p><p>\u30e6\u30fc\u30b6\u30fc\u3054\u3068\u306e\u6295\u7a3f\u6570\u304c\u8868\u793a\u3055\u308c\u307e\u3059\u3002.<\/p><h3><strong>SQL\u30d5\u30e9\u30b0\u30e1\u30f3\u30c8\u3092\u4f7f\u3063\u305fRails\u306e\u9ad8\u5ea6\u306a\u7d50\u5408<\/strong><\/h3><p>\u30a2\u30af\u30c6\u30a3\u30d6\u30ec\u30b3\u30fc\u30c9\u306e\u30d8\u30eb\u30d1\u30fc\u3060\u3051\u3067\u306f\u4e0d\u5341\u5206\u306a\u3053\u3068\u3082\u3042\u308b\u3002.<\/p><pre>User.joins(\"INNER JOIN posts ON posts.user_id = users.id AND posts.published = true\")<\/pre><p><strong>\u4f7f\u7528\u4f8b\uff1a<\/strong><\/p><ul><li>\u8907\u96d1\u306a\u6761\u4ef6<\/li><li>\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u30fb\u30c1\u30e5\u30fc\u30cb\u30f3\u30b0<\/li><\/ul><h3><strong>\u30b9\u30b3\u30fc\u30d7\u3067\u30b8\u30e7\u30a4\u30f3\u3092\u4f7f\u7528\u3059\u308b<\/strong><\/h3><p>\u30b9\u30b3\u30fc\u30d7\u306f\u30b8\u30e7\u30a4\u30f3\u3092\u518d\u5229\u7528\u53ef\u80fd\u306b\u3059\u308b\u3002.<\/p><pre><strong>\u30af\u30e9\u30b9<\/strong> \u30e6\u30fc\u30b6\u30fc &lt; ApplicationRecord\n  has_many <strong><em>\u6295\u7a3f<\/em><\/strong>\n\n\u00a0 \u7bc4\u56f2 <strong><em>:with_published_posts<\/em><\/strong>, -&gt; {\n    \u7d50\u5408(<strong><em>\u6295\u7a3f<\/em><\/strong>).where(<strong><em>\u6295\u7a3f<\/em><\/strong> { <strong><em>\u3092\u51fa\u7248\u3057\u305f\uff1a<\/em><\/strong> true })\n  }\n<strong>\u7d42\u308f\u308a<\/strong><\/pre><p><strong>\u4f7f\u7528\u6cd5\uff1a<\/strong><\/p><pre>\u30e6\u30fc\u30b6\u30fc.with_published_posts<\/pre><h3><strong>N+1\u30af\u30a8\u30ea\u30fc\u306e\u56de\u907f<\/strong><\/h3><p>N+1\u30af\u30a8\u30ea\u306f\u4e00\u822c\u7684\u306a\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u554f\u984c\u3067\u3042\u308b\u3002.<\/p><p><strong>\u60aa\u3044\u4f8b\u3060\uff1a<\/strong><\/p><pre>users = User.all\n\u30e6\u30fc\u30b6\u30fc <strong>\u3059\u308b<\/strong> |\u30e6\u30fc\u30b6\u30fc\n  user.posts.each <strong>\u3059\u308b<\/strong> |\u6295\u7a3f|post\n    puts post.title\n\u00a0 <strong>\u7d42\u308f\u308a<\/strong>\n<strong>\u7d42\u308f\u308a<\/strong><\/pre><p><strong>\u89e3\u6c7a\u7b56<\/strong><\/p><pre>User.includes()<strong><em>\u6295\u7a3f<\/em><\/strong>)<\/pre><h3><strong>\u30b8\u30e7\u30a4\u30f3 vs \u30a4\u30f3\u30af\u30eb\u30fc\u30c9 vs \u30d7\u30ea\u30ed\u30fc\u30c9<\/strong><\/h3><table width=\"528\"><thead><tr><th width=\"176\">\u65b9\u6cd5<\/th><th width=\"176\">\u76ee\u7684<\/th><th width=\"176\">SQL\u306e\u52d5\u4f5c<\/th><\/tr><\/thead><tbody><tr><td width=\"176\">\u30b8\u30e7\u30a4\u30f3\u30ba<\/td><td width=\"176\">\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0<\/td><td width=\"176\">INNER JOIN<\/td><\/tr><tr><td width=\"176\">\u5de6\u7d50\u5408<\/td><td width=\"176\">\u3059\u3079\u3066\u3092\u542b\u3080<\/td><td width=\"176\">\u5de6\u5916\u90e8\u7d50\u5408<\/td><\/tr><tr><td width=\"176\">\u3092\u542b\u3080\u3002<\/td><td width=\"176\">N+1\u3092\u907f\u3051\u308b<\/td><td width=\"176\">\u8907\u6570\u306e\u30af\u30a8\u30ea\u307e\u305f\u306fJOIN<\/td><\/tr><tr><td width=\"176\">\u30d7\u30ea\u30ed\u30fc\u30c9<\/td><td width=\"176\">\u5e38\u306b\u30af\u30a8\u30ea\u3092\u5206\u3051\u308b<\/td><td width=\"176\">JOIN\u306a\u3057<\/td><\/tr><\/tbody><\/table><h3><strong>\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u306b\u95a2\u3059\u308b\u8003\u5bdf<\/strong><\/h3><p><strong>1.\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u4f5c\u6210<\/strong><\/p><p>\u5916\u90e8\u30ad\u30fc\u304c\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u5316\u3055\u308c\u3066\u3044\u308b\u3053\u3068\u3092\u78ba\u8a8d\u3059\u308b\uff1a<\/p><pre>\u8ffd\u52a0\u30a4\u30f3\u30c7\u30c3\u30af\u30b9 <strong><em>\u6295\u7a3f<\/em><\/strong>, <strong><em>:user_id<\/em><\/strong><\/pre><p><strong>2.\u30aa\u30fc\u30d0\u30fc\u30d5\u30a7\u30c3\u30c1\u3092\u907f\u3051\u308b<\/strong><\/p><p>\u5217\u3092\u9650\u5b9a\u3059\u308b\u306b\u306f\u30bb\u30ec\u30af\u30c8\u3092\u4f7f\u3046\u3002.<\/p><p><strong>3.\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30ec\u30d9\u30eb\u306e\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0\u3092\u4f7f\u7528\u3059\u308b<\/strong><\/p><p>\u5e38\u306b\u30b8\u30e7\u30a4\u30f3\u304c\u3042\u308b\u72b6\u614b\u3092\u597d\u3080\u3002.<\/p><h3><strong>\u3088\u304f\u3042\u308b\u843d\u3068\u3057\u7a74<\/strong><\/h3><p><strong>1.\u91cd\u8907\u8a18\u9332<\/strong><\/p><p>\u5fc5\u8981\u306b\u5fdc\u3058\u3066.distinct\u3092\u4f7f\u7528\u3059\u308b\u3002.<\/p><p><strong>2.\u3042\u3044\u307e\u3044\u306a\u30b3\u30e9\u30e0<\/strong><\/p><p>\u30c6\u30fc\u30d6\u30eb\u63a5\u982d\u8f9e\u3092\u4f7f\u7528\u3059\u308b\uff1a<\/p><pre>select(\"users.id, posts.id AS post_id\")<\/pre><p><strong>3.\u9593\u9055\u3063\u305f\u7d50\u5408\u30bf\u30a4\u30d7<\/strong><\/p><p>join\u3068left_join\u306e\u9078\u629e\u306f\u614e\u91cd\u306b\u3002.<\/p><h3><strong>\u5b9f\u4f8b<\/strong><\/h3><p>3\u3064\u4ee5\u4e0a\u306e\u6295\u7a3f\u3092\u516c\u958b\u3057\u305f\u30e6\u30fc\u30b6\u30fc\u3092\u53d6\u5f97\u3059\u308b\uff1a<\/p><pre>\u30e6\u30fc\u30b6\u30fc.joins(<strong><em>\u6295\u7a3f<\/em><\/strong>)<br \/>\u00a0\u00a0\u00a0 .where(<strong><em>\u6295\u7a3f<\/em><\/strong> { <strong><em>\u3092\u51fa\u7248\u3057\u305f\uff1a<\/em><\/strong> true })<br \/>\u00a0\u00a0\u00a0 .group(\"users.id\")<br \/>\u00a0\u00a0\u00a0 .having(\"COUNT(posts.id) &gt; 3\")<\/pre><h3><strong>Rails\u7d50\u5408\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9<\/strong><\/h3><ul><li>\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0\u306b\u7d50\u5408\u3092\u4f7f\u7528\u3059\u308b<\/li><li>\u30a4\u30fc\u30ac\u30fc\u30ed\u30fc\u30c7\u30a3\u30f3\u30b0\u306b\u30a4\u30f3\u30af\u30eb\u30fc\u30c9\u3092\u4f7f\u7528<\/li><li>\u5e38\u306b\u30af\u30a8\u30ea\u306e\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u30c6\u30b9\u30c8\u3059\u308b<\/li><li>\u30af\u30a8\u30ea\u3092\u8aad\u307f\u3084\u3059\u304f\u3059\u308b<\/li><li>\u30b9\u30b3\u30fc\u30d7\u3092\u518d\u5229\u7528\u3059\u308b<\/li><\/ul><h2><strong>\u7d50\u8ad6<\/strong><\/h2><p>Rails\u306e\u7d50\u5408\u306fActive Record Query Interface\u306e\u5f37\u529b\u306a\u6a5f\u80fd\u3067\u3001\u958b\u767a\u8005\u306f\u8907\u6570\u306e\u30c6\u30fc\u30d6\u30eb\u306b\u307e\u305f\u304c\u308b\u95a2\u9023\u30c7\u30fc\u30bf\u3092\u52b9\u7387\u7684\u306b\u30af\u30a8\u30ea\u3067\u304d\u307e\u3059\u3002join\u3001left_join\u3001include\u306e\u9055\u3044\u3092\u7406\u89e3\u3059\u308b\u3053\u3068\u3067\u3001\u6700\u9069\u5316\u3055\u308c\u305f\u30b9\u30b1\u30fc\u30e9\u30d6\u30eb\u306a\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30af\u30a8\u30ea\u3092\u66f8\u304f\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002.<\/p><p>\u30b8\u30e7\u30a4\u30f3\u3092\u30de\u30b9\u30bf\u30fc\u3059\u308b\u3053\u3068\u306f\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5411\u4e0a\u3055\u305b\u308b\u3060\u3051\u3067\u306a\u304f\u3001\u6b21\u306e\u3088\u3046\u306a\u30e1\u30ea\u30c3\u30c8\u3082\u3042\u308b\u3002 <a href=\"https:\/\/www.railscarma.com\/ja\/%e3%82%ab%e3%82%b9%e3%82%bf%e3%83%a0%e3%83%ac%e3%83%bc%e3%83%ab%e3%82%a2%e3%83%97%e3%83%aa%e3%82%b1%e3%83%bc%e3%82%b7%e3%83%a7%e3%83%b3%e9%96%8b%e7%99%ba\/\">Rails\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3<\/a> \u3092\u3088\u308a\u4fdd\u5b88\u7684\u3067\u52b9\u7387\u7684\u306a\u3082\u306e\u306b\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u308b\u3002\u5c0f\u3055\u306a\u30a2\u30d7\u30ea\u3067\u3042\u308c\u3001\u5927\u898f\u6a21\u306a\u4f01\u696d\u30b7\u30b9\u30c6\u30e0\u3067\u3042\u308c\u3001join\u306e\u52b9\u679c\u7684\u306a\u4f7f\u3044\u65b9\u3092\u77e5\u308b\u3053\u3068\u306f\u6210\u529f\u306e\u305f\u3081\u306b\u4e0d\u53ef\u6b20\u3067\u3042\u308b\u3002.<\/p><p>RailsCarma\u306f\u5927\u624b\u4f01\u696d\u3067\u3042\u308b\u3002 <a href=\"https:\/\/www.railscarma.com\/ja\">Ruby on Rails\u958b\u767a\u4f1a\u793e<\/a> RailsCarma\u306f\u3001\u30b9\u30b1\u30fc\u30e9\u30d6\u30eb\u3067\u9ad8\u6027\u80fd\u306aWeb\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u69cb\u7bc9\u3092\u5c02\u9580\u3068\u3059\u308b\u4f01\u696d\u3067\u3059\u3002Active Record\u3068\u7d50\u5408\u306a\u3069\u306e\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u6700\u9069\u5316\u6280\u8853\u306b\u6df1\u3044\u5c02\u9580\u77e5\u8b58\u3092\u6301\u3064RailsCarma\u306f\u3001\u52b9\u7387\u7684\u306a\u30c7\u30fc\u30bf\u30a2\u30fc\u30ad\u30c6\u30af\u30c1\u30e3\u306e\u8a2d\u8a08\u3001\u30af\u30a8\u30ea\u8ca0\u8377\u306e\u8efd\u6e1b\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u306e\u5411\u4e0a\u3092\u652f\u63f4\u3057\u307e\u3059\u3002\u5f7c\u3089\u306e\u30c1\u30fc\u30e0\u306f\u3001\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u3001\u30af\u30ea\u30fc\u30f3\u30b3\u30fc\u30c9\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u91cd\u8996\u306e\u958b\u767a\u306b\u91cd\u70b9\u3092\u7f6e\u304d\u3001\u65b0\u8208\u4f01\u696d\u304b\u3089\u4f01\u696d\u307e\u3067\u3001\u5805\u7262\u3067\u4fdd\u5b88\u6027\u306e\u9ad8\u3044Rails\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3092\u63d0\u4f9b\u3057\u3066\u3044\u307e\u3059\u3002.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<\/div>\n\t\t  <div class=\"related-post slider\">\r\n        <div class=\"headline\">\u95a2\u9023\u8a18\u4e8b<\/div>\r\n    <div class=\"post-list owl-carousel\">\r\n\r\n            <div class=\"item\">\r\n            <div class=\"thumb post_thumb\">\r\n    <a  title=\"Offliberty Ruby Gem\u3068\u306f\uff1f\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/what-is-offliberty-ruby-gem-and-how-it-works\/?related_post_from=41304\">\r\n\r\n      <img decoding=\"async\" width=\"800\" height=\"300\" src=\"https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/What-is-Offliberty-Ruby-Gem-and-How-It-Works.png\" class=\"attachment-full size-full wp-post-image\" alt=\"\u30aa\u30d5\u30ea\u30d0\u30c6\u30a3\u30fb\u30eb\u30d3\u30fc\u30fb\u30b8\u30a7\u30e0\" srcset=\"https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/What-is-Offliberty-Ruby-Gem-and-How-It-Works.png 800w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/What-is-Offliberty-Ruby-Gem-and-How-It-Works-300x113.png 300w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/What-is-Offliberty-Ruby-Gem-and-How-It-Works-768x288.png 768w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/What-is-Offliberty-Ruby-Gem-and-How-It-Works-18x7.png 18w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/>\r\n\r\n    <\/a>\r\n  <\/div>\r\n\r\n  <a class=\"title post_title\"  title=\"Offliberty Ruby Gem\u3068\u306f\uff1f\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/what-is-offliberty-ruby-gem-and-how-it-works\/?related_post_from=41304\">\r\n        Offliberty Ruby Gem\u3068\u306f\uff1f  <\/a>\r\n\r\n        <\/div>\r\n              <div class=\"item\">\r\n            <div class=\"thumb post_thumb\">\r\n    <a  title=\"Rails\u306elink_to\u30e1\u30bd\u30c3\u30c9\uff1a\u4f8b\u306b\u3088\u308b\u5b8c\u5168\u30ac\u30a4\u30c9\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/rails-link_to-method-the-complete-guide-with-examples\/?related_post_from=41296\">\r\n\r\n      <img decoding=\"async\" width=\"800\" height=\"300\" src=\"https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/Rails-link_to-Method-The-Complete-Guide-with-Examples.png\" class=\"attachment-full size-full wp-post-image\" alt=\"Rails link_to\u30e1\u30bd\u30c3\u30c9\" srcset=\"https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/Rails-link_to-Method-The-Complete-Guide-with-Examples.png 800w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/Rails-link_to-Method-The-Complete-Guide-with-Examples-300x113.png 300w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/Rails-link_to-Method-The-Complete-Guide-with-Examples-768x288.png 768w, https:\/\/www.railscarma.com\/wp-content\/uploads\/2026\/04\/Rails-link_to-Method-The-Complete-Guide-with-Examples-18x7.png 18w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/>\r\n\r\n    <\/a>\r\n  <\/div>\r\n\r\n  <a class=\"title post_title\"  title=\"Rails\u306elink_to\u30e1\u30bd\u30c3\u30c9\uff1a\u4f8b\u306b\u3088\u308b\u5b8c\u5168\u30ac\u30a4\u30c9\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/rails-link_to-method-the-complete-guide-with-examples\/?related_post_from=41296\">\r\n        Rails\u306elink_to\u30e1\u30bd\u30c3\u30c9\uff1a\u4f8b\u306b\u3088\u308b\u5b8c\u5168\u30ac\u30a4\u30c9  <\/a>\r\n\r\n        <\/div>\r\n              <div class=\"item\">\r\n            <div class=\"thumb post_thumb\">\r\n    <a  title=\"Ruby on Rails\u3092\u4f7f\u3063\u3066\u30b9\u30b1\u30fc\u30e9\u30d6\u30eb\u306aSaaS\u30d7\u30e9\u30c3\u30c8\u30d5\u30a9\u30fc\u30e0\u3092\u69cb\u7bc9\u3059\u308b\u65b9\u6cd5\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/how-to-build-a-scalable-saas-platform-using-ruby-on-rails\/?related_post_from=41273\">\r\n\r\n      <img decoding=\"async\" width=\"800\" 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It simplifies database interactions by allowing you to write queries using Ruby instead of SQL. However, as applications grow, you often need to fetch data from multiple related tables. This is where joins come into play. In this guide, we will explore Rails joins in depth, understand how they work in the Active Record Query Interface, and learn how to use them efficiently in real-world scenarios. What Are Joins in Rails? A join is a database operation that combines rows from two or more tables based on a related column. In Rails, &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"https:\/\/www.railscarma.com\/ja\/%e3%83%96%e3%83%ad%e3%82%b0\/ruby-regex-match-guide-with-examples\/\"> <span class=\"screen-reader-text\">Ruby\u6b63\u898f\u8868\u73fe\u30de\u30c3\u30c1\u30ac\u30a4\u30c9\uff082026\uff09\u4f8b\u4ed8\u304d<\/span> \u3082\u3063\u3068\u8aad\u3080 \"<\/a><\/p>","protected":false},"author":5,"featured_media":41232,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1224],"tags":[],"class_list":["post-41226","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.8 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Rails Joins: A Complete Guide to Active Record Query Interface<\/title>\n<meta name=\"description\" content=\"Master Rails joins with this complete guide to the Active Record query interface. 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