Question

我有一张包含语言的表格。

表格

lan_dish_id | lan_dish_lang | lan_dish_dishid | lan_dish_mainlang
--------------- | ------------------- | --------------------- | ------------------------
1 | nl | 8 | 1
4 | fr | 8 | 0

我需要检查表中是否有$_SESSION['lang']中的语言，否则它必须采用主语言。

不幸的是，当运行以下查询时，他返回带FR的行以及NL als lan_dish_lan ...在这种情况下，它只返回带有FR的行。

SELECT * FROM `language_dish` WHERE 
(CASE
 WHEN lan_dish_lang = "fr"
 THEN lan_dish_lang = "fr"
 ELSE lan_dish_mainlang = 1
 END) AND lan_dish_dishid = 8

Answer 1

这里有两种可能对你有用的方法。

/*
DROP TABLE IF EXISTS T;

CREATE TABLE T (lan_dish_id INT, lan_dish_lang VARCHAR(2), lan_dish_dishid INT, lan_dish_mainlang INT);
*/
truncate table t;
INSERT INTO T VALUES
(1                 , 'nl' , 8,                         1) ,
(4                 , 'fr' , 8,                         0) ,
(5                 , 'nl' , 9,                         1) ,
(6                 , 'de' , 7,                         0) 

;

select s.lan_dish_dishid, left(gc,instr(concat(gc,','),',') -1) lang
from
(
select lan_dish_dishid, group_concat(lan_dish_lang order by lan_dish_mainlang) gc
from t
#where lan_dish_dishid = 8
group by lan_dish_dishid
order by lan_dish_dishid
) s
;
select s.lan_dish_id, s.lan_dish_lang
from
(
select t.*,
         if(t.lan_dish_dishid <> @p , @rn:=1,@rn:=@rn+1) rn,
         @p:= t.lan_dish_dishid p
from t , (select @rn:=0,@p:=0) r
order by t.lan_dish_dishid, t.lan_dish_Mainlang
) s where s.rn = 1

结果

+-------------+---------------+
| lan_dish_id | lan_dish_lang |
+-------------+---------------+
|           6 | de            |
|           4 | fr            |
|           5 | nl            |
+-------------+---------------+
3 rows in set (0.01 sec)

在WHERE Mysql查询中的CASE

1 个答案: