where_in和find_in_set之间的区别 [英] difference between where_in and find_in_set

问题描述

我正在处理一个联接查询，其中我必须从包含逗号分隔值的列中获取数据.例如allowed_activity contains 1,2,3,4,5,6 这是允许的activity_id.

I am working on a join query in which I have to get the data from a column which contain the comma separated values.like allowed_activity contain 1,2,3,4,5,6 this the activity_id which is allowed.

因此，在查询中，我正在检查是否允许当前活动，为此，我使用了where_in并在where条件下尝试了find_in_set.

So In the query, I am checking that current activity is allowed or not and for that, I have used where_in and also tried find_in_set in where condition.

这是查询的一部分:

$this->db->where_in('a.allowed_activity',$activity_id);
//And With FIND_IN_SET
$this->db->where("FIND_IN_SET($activity_id, a.allowed_activity) !=",0);

问题或困惑

当我使用where_in时，它不会给我结果.但是，如果使用FIND_IN_SET，它将返回所需的结果.我以为where_in可以完成任务，但没有.

Problem or Confusion

When I use where_in it doesn't give me the result. But if I use FIND_IN_SET then it will return the desired result. I thought that where_in can do the task but it didn't.

只是想知道为什么find_in_set的工作方式不同于 where_in 由于这两个功能的工作原理与查找数据的方法相同，所以用逗号分隔列表中.

Just Want to know why find_in_set working differently than where_in Because of both the function work same as finding the data is in comma separated list.

这是完整的查询:

SELECT mycolumns
FROM `table1` as `ea`
LEFT OUTER JOIN `table2` as `a` ON `ea`.`package_id` = `a`.`id`
LEFT OUTER JOIN `table3` as `e` ON `ea`.`employer_id` = `e`.`id`
WHERE `ea`.`card_id` > 0
AND FIND_IN_SET(6, a.allowed_activity) !=0
AND `ea`.`id` = '6'
ORDER BY `ea`.`creation_date` DESC

我正在使用Codeigniter Active记录.

I am using Codeigniter Active record.

推荐答案

WHERE IN要求在查询中按字面值指定一组值，而不是包含逗号分隔字符串的单个值.如果您写:

WHERE IN requires the set of values to be specified literally in the query, not as a single value containing a comma-delimited string. If you write:

WHERE 6 IN (a.allowed_activity)

它将a.allowed_activity视为单个值，并将其与6进行比较，而不是将其作为多个要搜索的值的集合.

it will treat a.allowed_activity as just a single value, and compare it with 6, not as a set of multiple values to search.

FIND_IN_SET在逗号分隔的字符串中搜索值.

FIND_IN_SET searches a comma-delimited string for the value.

另一种查看方式是IN是结合OR的一堆=测试的快捷方式:

Another way to view it is that IN is a shortcut for a bunch of = tests combined with OR:

WHERE x IN (a, b, c, d)

是

WHERE x = a OR x = b OR x = c OR x = d

以这种方式重写它时，您可以清楚地知道为什么它不适用于包含逗号分隔的字符串的列.它只是翻译

When you rewrite it like this, you can see clearly why it won't work with a column containing a comma-delimited string. It simply translates

WHERE 6 IN (a.allowed_activity) 

收件人:

WHERE 6 = a.allowed_activity

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