diff --git a/server/migrations/2023_06_29_220600_create_chats_table.sql b/server/migrations/2023_06_29_220600_create_chats_table.sql
new file mode 100644
index 0000000..b53e97d
--- /dev/null
+++ b/server/migrations/2023_06_29_220600_create_chats_table.sql
@@ -0,0 +1,27 @@
+CREATE TABLE
+    IF NOT EXISTS
+goatoh_training.chats
+(
+  id
+    INT
+    NOT NULL
+    AUTO_INCREMENT
+    COMMENT '主キー',
+
+  user_id
+    INT
+    NOT NULL
+    COMMENT 'ユーザのキー',
+
+  text
+    TEXT
+    CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci
+    NOT NULL
+    COMMENT 'チャット・テキスト',
+
+  PRIMARY KEY (id)
+)
+ENGINE = InnoDB
+CHARSET = utf8mb4 COLLATE utf8mb4_general_ci
+COMMENT = 'チャット';
+
diff --git a/server/migrations/2023_06_29_224300_create_users_table.sql b/server/migrations/2023_06_29_224300_create_users_table.sql
new file mode 100644
index 0000000..4b7c27d
--- /dev/null
+++ b/server/migrations/2023_06_29_224300_create_users_table.sql
@@ -0,0 +1,22 @@
+CREATE TABLE
+    IF NOT EXISTS
+goatoh_training.users
+(
+  id
+    INT
+    NOT NULL
+    AUTO_INCREMENT
+    COMMENT '主キー',
+
+  name
+    VARCHAR(30)
+    CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci
+    NOT NULL
+    COMMENT 'ユーザ名',
+
+  PRIMARY KEY (id)
+)
+ENGINE = InnoDB
+CHARSET = utf8mb4 COLLATE utf8mb4_general_ci
+COMMENT = 'ユーザ';
+
diff --git a/server/modules/chat.mod.php b/server/modules/chat.mod.php
new file mode 100644
index 0000000..b1ff0ba
--- /dev/null
+++ b/server/modules/chat.mod.php
@@ -0,0 +1,40 @@
+<?php
+
+class
+Chat
+{
+  var $db;
+
+  function
+  __construct ()
+  {
+    $config = include (__DIR__ . '/config.php');
+
+    $db_host = $config['host'];
+    $db_port = $config['port'];
+    $db_user = $config['user'];
+    $db_pass = $config['pass'];
+
+    $this -> db = new mysqli ($db_host, $db_user, $db_pass, 'goatoh_training',
+                              $db_port);
+  }
+
+  function
+  sendChat (
+      int     $user_id,
+      string  $text):
+  void
+  {
+    $sql = "
+        INSERT INTO
+          chats (
+            id,
+            text)
+          VALUES
+            (
+              $user_id,
+              '$text')";
+    $this -> db -> query ($sql) or die ("db_insert error $sql");
+  }
+}
+
diff --git a/server/modules/common.mod.php b/server/modules/common.mod.php
deleted file mode 100644
index 8aafd26..0000000
--- a/server/modules/common.mod.php
+++ /dev/null
@@ -1,21 +0,0 @@
-<?php
-
-class
-Common
-{
-  var $db;
-
-  function
-  __construct ()
-  {
-    $config = include (__DIR__ . '/config.php');
-
-    $db_host = $config['host'];
-    $db_port = $config['port'];
-    $db_user = $config['user'];
-    $db_pass = $config['pass'];
-
-    $this -> db = new mysqli ($db_host, $db_user, $db_pass, 'goatoh_training', $db_port);
-  }
-}
-