Question

我正在编写一个访客计数器。它是 PHP5 / SQLite3 组合。

制作了两个数据库表，一个用于访问者，另一个用于点击。结构和样本数据：

CREATE TABLE 'visitors' (
'id' INTEGER DEFAULT NULL PRIMARY KEY AUTOINCREMENT,
'ip' TEXT DEFAULT NULL,
'hash' TEXT DEFAULT NULL,
UNIQUE(ip)
);

INSERT INTO "visitors" ("id","ip","hash") VALUES ('1','1.2.3.4','f9702c362aa9f1b05002804e3a65280b');
INSERT INTO "visitors" ("id","ip","hash") VALUES ('2','1.2.3.5','43dc8b0a4773e45deab131957684867b');
INSERT INTO "visitors" ("id","ip","hash") VALUES ('3','1.2.3.6','9ae1c21fc74b2a3c1007edf679c3f144');

CREATE TABLE 'hits' (
'id' INTEGER DEFAULT NULL PRIMARY KEY AUTOINCREMENT,
'time' INTEGER DEFAULT NULL,
'visitor_id' INTEGER DEFAULT NULL,
'host' TEXT DEFAULT NULL,
'location' TEXT DEFAULT NULL
);

INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('1','1418219548','1','localhost','/some/path/example.php');
INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('2','1418219550','1','localhost','/some/path/example.php');
INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('3','1418219553','1','localhost','/some/path/example.php');
INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('4','1418219555','2','localhost','/some/path/example.php');
INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('5','1418219557','1','localhost','/some/path/example.php');
INSERT INTO "hits" ("id","time","visitor_id","host","location") VALUES ('6','1418219558','3','localhost','/some/path/example.php');

我现在想要获取访问者数据，但仅限于那些在过去30秒内处于活动状态的人。我需要以下数据作为输出，这里以用户ID 1为例：

$visitor = Array(
    [id] => 1
    [ip] => 1.2.3.4
    [hash] => f9702c362aa9f1b05002804e3a65280b
    [first_hit] => 1418219548
    [last_hit] => 1418219557
    [last_host] => localhost
    [last_location] => /some/path/example.php
    [total_hits] => 4
    [idle_since] => 11
)

我会用我当前的查询得到这个，一切都很好，但是你可以看到我需要很多次选择：

SELECT 
   visitors.id,
   visitors.ip,
   visitors.hash,
   (SELECT hits.time FROM hits WHERE hits.visitor_id = visitors.id ORDER BY hits.id ASC LIMIT 1) AS first_hit,
   (SELECT hits.time FROM hits WHERE hits.visitor_id = visitors.id ORDER BY hits.id DESC LIMIT 1) AS last_hit,
   (SELECT hits.host FROM hits WHERE hits.visitor_id = visitors.id ORDER BY hits.id DESC LIMIT 1) AS last_host,
   (SELECT hits.location FROM hits WHERE hits.visitor_id = visitors.id ORDER BY hits.id DESC LIMIT 1) AS last_location,
   (SELECT COUNT(hits.id) FROM hits WHERE hits.visitor_id = visitors.id) AS total_hits,
   (SELECT strftime('%s','now') - hits.time FROM hits WHERE hits.visitor_id = visitors.id ORDER BY hits.id DESC LIMIT 1) AS idle_since
FROM visitors
WHERE idle_since < 30
ORDER BY last_hit DESC

所以，这对我的用例是否可以，或者你知道更好的方法从这两个表中获取这些数据吗？我已经玩过JOINS，但不管我怎么调整它，COUNT（）给了我错误的输出，例如用户ID 1只有一个总命中。

我可能不得不重新建模数据库，如果我想正确使用JOINS，我想。

更新：基于AeroX'答案我已经构建了新查询。它基本上只有一个小bug。你不能在WHERE子句中有MAX（）。在GROUPING之后使用HAVING。我还使用EXPLAIN和EXPLAIN QUERY PLAN测试了旧的和新的。看起来好多了。谢谢你们！

SELECT
    V.id,
    V.ip,
    V.hash,
    MIN(H.time) AS first_hit,
    MAX(H.time) AS last_hit,
    strftime('%s','now') - MAX(H.time) AS idle_since,
    COUNT(H.id) AS total_hits,
    LH.host AS last_host,
    LH.location AS last_location
FROM visitors AS V

INNER JOIN hits AS H ON (V.id = H.visitor_id)

INNER JOIN (
    SELECT visitor_id, MAX(id) AS id
    FROM hits
    GROUP BY visitor_id
) AS L ON (V.id = L.visitor_id)

INNER JOIN hits AS LH ON (L.id = LH.id)

GROUP BY V.id, V.ip, V.hash, LH.host, LH.location

HAVING idle_since < 30

ORDER BY last_hit DESC

Answer 1

衡量查询效果的最佳方法之一是使用explain。

来自sqlite

EXPLAIN QUERY PLAN SQL命令用于获取高级别 SQLite用于实现的策略或计划的描述特定的SQL查询。最重要的是，EXPLAIN QUERY PLAN报告查询使用数据库索引的方式。这份文件是理解和解释EXPLAIN QUERY PLAN输出的指南。背景信息可单独获得：
Notes on the query optimizer.
How indexing works.
The next generation query planner. 
EXPLAIN QUERY PLAN命令返回零行或多行四行   各列。列名是“selectid”，“order”，“from”，   “详情”。前三列包含整数值。决赛   列，“细节”，包含一个文本值，其中包含大部分内容   有用的信息。

EXPLAIN QUERY PLAN在SELECT语句中最有用，但也可能   与其他从数据库表中读取数据的语句一起出现   （例如UPDATE，DELETE，INSERT INTO ... SELECT）。

explain查询的示例是：

EXPLAIN SELECT * FROM COMPANY WHERE Salary >= 20000;

http://www.tutorialspoint.com/sqlite/sqlite_explain.htm

以下是更复杂的用法示例。

How can I analyse a Sqlite query execution?

Answer 2

您可能想要清理它，但这应该让您了解如何进行连接以及如何使用GROUP BY语句聚合每个访问者的命中表。这应该比使用大量子查询更有效。

我已经加入了关于联接的评论，以便您了解我为什么要制作它们。

SELECT 
   V.id,
   V.ip,
   V.hash,
  MIN(H.time) AS first_hit,
  MAX(H.time) AS last_hit,
  COUNT(H.id) AS total_hits,
  strftime('%s','now') - MAX(H.time) AS idle_since,
  LH.host AS last_host,
  LH.location AS last_location
FROM visitors AS V
-- Join hits table so we can calculate aggregates (MIN/MAX/COUNT)
INNER JOIN hits AS H ON (V.id = H.visitor_id)
-- Join a sub-query as a table which contains the most recent hit.id for each visitor.id
INNER JOIN (
  SELECT visitor_id, MAX(id) AS id
  FROM hits
  GROUP BY visitor_id
) AS L ON (V.id = L.visitor_id)
-- Use the most recent hit.id for each visitor.id to fetch that most recent row (for last_host/last_location)
INNER JOIN hits AS LH ON (L.id = LH.id)
GROUP BY V.id, V.ip, V.hash, LH.host, LH.location
HAVING idle_since < 30
ORDER BY last_hit DESC

这个SQLite查询有效吗？

2 个答案: