PHP 배열 집합 연산
$arr1 = array('a', 'b', 'c', 'd'); $arr2 = array('c', 'd', 'e', 'f'); 1. 합집합 $arr = array_unique(array_merge($arr1, $arr2)); 2. 교집합 $arr = array_values(array_intersect($arr1, $arr2)); 3. 차집합 $arr = array_values(array_diff($arr1, $arr2)); 4. 대칭차집합 $arr = array_values(array_diff(array_merge($arr1, $arr2), array_intersect($arr1, $arr2)));
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Mysql 테이블 조인 쿼리
SELECT a.col1, a.col2, a.col3, ... FROM tableA a LEFT JOIN tableB b on a.key = b.key SELECT a.col1, a.col2, a.col3, ... FROM tableA a RIGHTJOIN tableB b on a.key = b.key SELECT a.col1, a.col2, a.col3, ... FROM tableA a INNER JOIN tableB b on a.key = b.key SELECT a.col1, a.col2, a.col3, ... FROM tableA a LEFT JOIN tableB b on a.key = b.key WHERE b.key IS NULL SELECT a.col1, a.col2, a.col3, ... FR..
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