if($keyword){ //키워드 검색
    $WHEREIS .= " and c_uid IN (SELECT uid FROM q_pr@@@@@@t where subject like '".$keyword."%' or esubject like '".$keyword."%' or subject like '%".$keyword."%' or esubject like '%".$keyword."%' or kewordinfo like '%".$keyword."%' )";

val IN ( 조건, 조건, 조건)

group by ~ having (조건 )

ordery by case when 조건1 then 결과1

when 조건2 then 결과2

~~

else 결과 end

SELECT a, CASE
             WHEN b = '*' THEN 'star'
             WHEN b = '+' THEN 'plus'
             WHEN b = '-' THEN 'minus'
             ELSE '????'
          END AS B
  FROM test_case_when;

출처: https://joke00.tistory.com/103 [Smile virus]