WITH A AS(
SELECT CASE WHEN (MOD(COUNT(*),2) )=0 THEN COUNT(*)/2 ELSE COUNT(*)/2 +1 END A
,CASE WHEN (MOD(COUNT(*),2) )=0 THEN COUNT(*)/2 +1 ELSE COUNT(*)/2 +1 END B
FROM CONVENIENCE WHERE SURVEY_YEAR ='2019' AND KIND_CODE ='100'
)
SELECT ROUND(cast(SUM(TOTAL_VALUE)AS REAL)/2 ,0) AS SA_MEDIAN 
FROM (
 SELECT TOTAL_VALUE,row_number() over (order by TOTAL_VALUE DESC) as 順位
 FROM CONVENIENCE
 WHERE SURVEY_YEAR ='2019' AND KIND_CODE ='100'
) A
WHERE 順位 = (SELECT A FROM A)
OR 順位 = (SELECT B FROM A)