Question

我有下表

id    site_id    language_id    paragraph
 1          1              1    french text
 2          1              2    english text
 3          2              1    french text 
 4          2              3    spanish text

我想让查询返回段落给出site_id language_id，如：

SELECT paragraph FROM mytable WHERE site_id = givenSite AND
language_id =
if exists language_id = givenLanguage then givenLanguage
else if exists language_id = 2 then 2
else 1

我的工作方式如下，但我希望我们能写出更好的查询：

DECLARE @site int, $language int  
SET @site = 1  
SET @language = 3  

SELECT CASE 
      WHEN EXISTS(SELECT paragraph_0
                  FROM   tablename
                  WHERE  language_id = @language AND site_id = @site)
              THEN (SELECT paragraph_0
                    FROM   tablename 
                    WHERE  language_id = @language AND site_id = @site)
              ELSE (
                SELECT CASE 
                WHEN EXISTS(SELECT paragraph_0
                            FROM   tablename
                            WHERE  language_id = 2 AND site_id = @site)
                THEN (SELECT paragraph_0
                      FROM   tablename 
                      WHERE  language_id = 2 AND site_id = @site)
                ELSE (SELECT paragraph_0
                      FROM   tablename 
                      WHERE  language_id = 1 AND site_id = @site)
                END)
END

我试着写here但对不起，我不明白如何在sqlfiddle中声明变量。

Answer 1

我认为这对你有用：

SELECT paragraph_0, IF(language_id = givenLanguage, 1, 0) AS isGivenLanguage
FROM tablename 
WHERE site_id = 3 AND language_id IN (1, 2, givenLanguage)
ORDER BY isGivenLanguage DESC, language_id DESC
LIMIT 1

Answer 2

这是一种方式。

require(["js/rsvp", "bootstrap"], function (RSVP) {

http://sqlfiddle.com/#!2/1c5fd4/20

更好地使用耙系统

set @site := 1 ;
set @language := 3  ;
select
language_id,paragraph_0 from (
  select language_id,paragraph_0 from tablename where site_id =@site and language_id = @language
  union 
  select language_id,paragraph_0 from tablename where site_id =@site and language_id <> @language
)x
order by language_id desc limit 1;

http://sqlfiddle.com/#!2/1c5fd4/24

来自评论

例如，如果我正在寻找网站3的语言5.如搜索语言不存在它应该寻找英语，但英语不是存在它应该返回强制存在的法语

这将非常简单，如下所示，看起来你已经明白了。

set @site := 1 ;
set @language := 3  ;
select
rank,paragraph_0 from (
  select 0 as rank, paragraph_0 from tablename where site_id =@site and language_id = @language
  union 
  select rank,paragraph_0 from(
    select @rn:= @rn+1 as rank ,paragraph_0 , language_id
    from tablename,(select @rn:=0)x where site_id =@site and language_id <> @language
    order by language_id desc 
  )x
)x
order by rank limit 1;

如何根据现有字段值创建返回行的MySQL查询？

2 个答案: