Question

我有一个带有以下列的MySQL数据库表

ID
status (can contain values 0, 1, 2)
timepstamp
text
note
owner

我想从表格中获取有关非特定所有者条目的以下信息：

 number of entries
 number of entries where status=0
 number of entries where status=1
 number of entries where status=2
 number of entries where LENGTH(note)>0
 minimum timestamp
 maximum timestamp

我曾经阅读完整的数据集，然后使用

用PHP评估它们

SELECT status, timestamp, LENGTH(note)>0 WHERE owner="name";

我遇到的问题是，有些用户有这么多条目，如果我将数据读入PHP，我经常会出现内存不足错误。我认为让MySQL评估数据应该更有效。我无法编写可以完成此任务的查询。

SELECT
    MIN(timestamp) AS mintime,
    MAX(timestamp) AS maxtime,
    COUNT(*) AS number,
    ...
WHERE owner="name"

是否有可能一次性获得结果？例如，嵌套的WHERE或IF在COUNT？

中

    COUNT(WHERE status=0) AS inactive
    COUNT(IF(status=1)) AS active
    ...

你会如何解决这个问题？

Answer 1

试一试 -

SELECT
    COUNT(*) AS total,
    SUM(IF(status=0, 1, 0)) AS stat0,
    SUM(IF(status=1, 1, 0)) AS stat1,
    SUM(IF(status=2, 1, 0)) AS stat2,
    SUM(IF(LENGTH(note)>0, 1, 0)) AS notes,
    MIN(timestamp) AS mintime, 
    MAX(timestamp) AS maxtime
FROM tbl_name
WHERE owner="name"
GROUP BY owner

Answer 2

试试这个：

SELECT
MIN(`timestamp`) AS `mintime`,
MAX(`timestamp`) AS `maxtime`,
COUNT(`ID`) AS `number`,
(SELECT COUNT(`ID`) FROM `Table` WHERE `owner` = 'owner' AND `status` = 0) AS `inactive`,
(SELECT COUNT(`ID`) FROM `Table` WHERE `owner` = 'owner' AND `status` = 1) AS `active`,
(SELECT COUNT(`ID`) FROM `Table` WHERE `owner` = 'owner' AND LENGTH(`note`)>0) AS `longentries`
FROM `Table`
WHERE `owner` = 'name'

您应该考虑规范化数据库设计，这样您就可以有两个单独的表，一个用于用户，一个用于条目，如下所示：

USERS ID 名称状态

ENTRIES ID 用户身份时间戳文本 note（如果这是特定于条目的字段;否则将其移至表USERS）

希望这有帮助。

从MySQL数据库中读取评估数据

2 个答案: