Question

我正在尝试构建一个支持系统，我现在面临一个复杂的查询。我的SQLite表中有几张表看起来像这样（略微简化）：

CREATE TABLE "assign" (
             "id" INTEGER NOT NULL PRIMARY KEY, 
        "created" DATETIME NOT NULL, 
    "is_assigned" SMALLINT NOT NULL, 
        "user_id" INTEGER NOT NULL REFERENCES "user" ("id")
);
CREATE TABLE "message" (
             "id" INTEGER NOT NULL PRIMARY KEY, 
        "created" DATETIME NOT NULL, 
        "user_id" INTEGER REFERENCES "user" ("id") , 
           "text" TEXT NOT NULL
);
CREATE TABLE "user" (
             "id" INTEGER NOT NULL PRIMARY KEY, 
           "name" VARCHAR(255) NOT NULL
);

我现在想做一个查询，它给我*一个用户列表，最后创建的Assign.is_assigned == False，最后创建的Message晚于最后创建的Assign *。所以我现在有以下（伪）查询：

SELECT * 
FROM user
WHERE ((IF (
        SELECT is_assigned 
          FROM assign 
         WHERE assign.user_id = user.id 
      ORDER BY created DESC LIMIT 1
       ) = False)
      AND ((
        SELECT created 
          FROM message 
         WHERE message.user_id = user.id 
      ORDER BY created DESC 
         LIMIT 1
        ) > (
        SELECT created 
          FROM assign 
         WHERE assign.user_id = user.id 
      ORDER BY created DESC 
         LIMIT 1))
);

这对我来说很有意义，但遗憾的是没有给电脑。我想我需要使用case语句甚至连接或者什么，但我不知道如何。有没有人知道如何做到这一点？

Answer 1

尝试以下我在mysql中创建的查询

SELECT u.id AS 'user',u.name AS 'User_Name', ass.created AS 'assign_created',ass.is_assigned AS 'is_assigned',
msg.created AS 'message_created'
FROM `user` AS u
LEFT JOIN `assign` AS ass ON ass.`user_id` = u.`id`
LEFT JOIN `message` AS msg ON msg.`user_id` = u.id
LEFT JOIN (SELECT u.id AS 'user_id',u.name AS 'username',ass.created AS 'max_ass_created',ass.is_assigned AS 'assigned'
FROM `user` AS u
LEFT JOIN `assign` AS ass ON ass.`user_id` = u.`id`
LEFT JOIN `message` AS msg ON msg.`user_id` = u.`id`
GROUP BY u.id ORDER BY ass.created DESC) AS sub ON sub.user_id = u.id
WHERE (sub.assigned IS FALSE AND msg.created < sub.max_ass_created)

检查您的方案的 SQL Fiddle

希望这能解决您的问题！

Answer 2

你不需要那里的IF，而且SQLite没有False，但是，你的查询是非常正确的：

SELECT *
FROM "user"
WHERE NOT (SELECT is_assigned 
             FROM assign 
            WHERE user_id = "user".id 
         ORDER BY created DESC
            LIMIT 1)
  AND (SELECT created 
         FROM message 
        WHERE user_id = "user".id 
     ORDER BY created DESC 
        LIMIT 1
      ) > (
       SELECT created 
         FROM assign 
        WHERE user_id = "user".id 
     ORDER BY created DESC 
        LIMIT 1)

SQLite中的复杂条件SQL语句

2 个答案: