使用 CASE 声明，这应该是可能的。
试试这个：

SELECT
    LNG.id                                          AS language_id,
    LNG.language_name                               AS language_name,
    LNG.language_code                               AS language_code,
    CLP.is_default                                  AS id_default_language

FROM Country_Language_Preference                    AS CLP
INNER JOIN Country                                 AS CNT
      ON CLP.country_id = CNT.id
INNER JOIN Languages                               AS LNG
      ON CLP.language_id = LNG.id
WHERE
      CNT.country_name = CASE WHEN @Country = "Senegal" OR @Country = "Rwanda" THEN "Senegal"
                         ELSE "GLOBAL" END

简单使用 OR :

WHERE (CNT.country_name = @country OR @country = 'GLOBAL')
``` `@country` 是你传递的参数。
如果你想限制在这两个国家，那么：

WHERE (CNT.country_name = @country OR
(@country NOT IN ('Rwanda', 'Senegal') AND CNT.country_name = 'GLOBAL')
)

但第一个版本似乎更通用。