MySql 根据逗号分隔值的输入更新计数

Question

如果我要向 MySql 提供一个逗号分隔的字符串，如 ('US,UK,CA') (通过 php 脚本来自表单)，我怎样才能让 MySql 循环该字符串并进行计数那里的每个国家/地区代码并更新不同的表，其中该表中的国家/地区代码等于字符串中的国家/地区代码。

示例:

表_a

"id"    "countries"
"1"     "US,CA"
"2"     "US,CA"
"3"     "US,AU"
"4"     "US,UK"
"5"     "US"

表_b

"id"    "country"   "total"
"1"     "US"        "0"
"2"     "CA"        "0"
"3"     "UK"        "0"
"4"     "AU"        "0"

我该怎么办:

例如:如果我提供 ('US,UK,CA')

update table_b set country = (

    select count(id) from table_a where country = (// each country in that string ('US,UK,CA'))

) where country = (country currently selected from the string above)

这样的事情可以做吗？如果只有一个国家，它就可以正常工作。当有更多的时候我该怎么办？

最后，我希望得到这样的结果:

table_b
"id"    "country"   "total"
"1"     "US"        "5" // There are 5 in table_a
"2"     "CA"        "2" // There are 2 in table_a
"3"     "UK"        "1" // Only 1 in table_a
"4"     "AU"        "1" // Only 1 in table_a

Answer 1

尝试对“CA”县进行此操作:

 update table2 
 set total = (

select count(*) from table1 where FIND_IN_SET(country, countries)
)

DEMO

或者按一个国家/地区

 update table2 
 set total = (

  select count(*) from table1 where FIND_IN_SET('CA', countries)
 )
  WHERE country = 'CA'

DEMO

编辑:我不知道您到底在寻找什么，但如果您需要特殊的国家/地区。只需添加 WHERE 子句

   update table2 
 set total = (

 select count(*) from table1 where FIND_IN_SET(country, countries)
 )
 WHERE country IN ('US','UK','CA')

DEMO