LEFT JOIN用法,好久没用过原生sql了
//left join(左联接) 返回包括左表中的所有记录和右表中联结字段相等的记录//取出文章表的id title字段 栏目表的栏目id栏目名(name)字段 文章表clas_id-关联栏目表ID条件文章表id大于30 栏目ID小于22
$sql = "SELECT problem.id,problem.title,cate.id AS cateid,cate.name AS catename
FROM dp_problem AS problem lEFT JOIN dp_class_hyw AS cate
ON problem.class_id = cate.id WHERE problem.id > 25 AND cate.id
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