Question

仅当成员不在另一个列表中时，我才尝试创建一个成员列表。当另一个列表中至少有一个成员时，查询将起作用（返回不在另一个列表中的成员）。但是，当另一个列表不包含任何成员（返回NULL）时，则不会返回任何值。

String selectQry = ("SELECT at_cub_details.cd_id, at_cub_details.cd_surname, at_cub_details.cd_first_name, " +
            "at_cub_details.cd_archived " +
            "FROM at_cub_details, at_account_group " + 
            "WHERE at_account_group.acc_id = ? AND at_account_group.grp_id = at_cub_details.grp_id " +
                "AND ( " +
                    " SELECT at_cub_details.cd_id " +
                          "FROM at_group, at_account_group group1, at_account_group group2, at_accounts " + 
                          "LEFT JOIN at_account_cub_association ON at_accounts.acc_id = at_account_cub_association.acc_id " +
                          "LEFT JOIN at_cub_details ON at_account_cub_association.cd_id = at_cub_details.cd_id " +
                          "WHERE (at_accounts.acc_id = ? " +
                            "AND (group1.acc_id = ?  " +
                            "AND group1.grp_id = group2.grp_id " +
                            "AND group2.acc_id = at_accounts.acc_id)) " +
                            "AND (group2.grp_id = at_group.grp_id) LIMIT 1) IS NOT NULL " +
                "AND at_cub_details.cd_id NOT IN ( " +
                                " SELECT at_cub_details.cd_id " +
                                      "FROM at_group, at_account_group group1, at_account_group group2, at_accounts " + 
                                      "LEFT JOIN at_account_cub_association ON at_accounts.acc_id = at_account_cub_association.acc_id " +
                                      "LEFT JOIN at_cub_details ON at_account_cub_association.cd_id = at_cub_details.cd_id " +
                                      "WHERE (at_accounts.acc_id = ? " +
                                        "AND (group1.acc_id = ?  " +
                                        "AND group1.grp_id = group2.grp_id " +
                                        "AND group2.acc_id = at_accounts.acc_id)) " +
                                        "AND (group2.grp_id = at_group.grp_id)) " +
            "ORDER BY at_cub_details.cd_surname, at_cub_details.cd_first_name;");

好的，为简化第二个和第三个“ SELECT”的工作，第一个“ SELECT”仅在第三个“ SELECT”返回值时才起作用，而在返回“ NULL”时不起作用。最初，我只有第三个“ SELECT”。然后，我添加了第二个“ SELECT”来首先检查“ NULL”。但是，这不能解决问题。所以：

这有效：

String selectQry = ("SELECT at_cub_details.cd_id, at_cub_details.cd_surname, at_cub_details.cd_first_name, " +
            "at_cub_details.cd_archived " +
            "FROM at_cub_details, at_account_group " + 
            "WHERE at_account_group.acc_id = ? AND at_account_group.grp_id = at_cub_details.grp_id " +
                "AND at_cub_details.cd_id NOT IN ( '20' ) " +
            "ORDER BY at_cub_details.cd_surname, at_cub_details.cd_first_name;");

这不起作用：

String selectQry = ("SELECT at_cub_details.cd_id, at_cub_details.cd_surname, at_cub_details.cd_first_name, " +
            "at_cub_details.cd_archived " +
            "FROM at_cub_details, at_account_group " + 
            "WHERE at_account_group.acc_id = ? AND at_account_group.grp_id = at_cub_details.grp_id " +
                "AND at_cub_details.cd_id NOT IN ( NULL ) " +
            "ORDER BY at_cub_details.cd_surname, at_cub_details.cd_first_name;");

关于您是否对我投反对票，我并不在乎，因为我这样做不是为了牟利和学习（我不是程序员）。

Answer 1

CodeRanch的员工非常乐于助人。答案是，如果为null，则使用“ IFNULL”返回0，而不是检查NULL。

String selectQry = ("SELECT at_cub_details.cd_id, at_cub_details.cd_surname, at_cub_details.cd_first_name, " +
                "at_cub_details.cd_archived " +
                "FROM at_cub_details, at_account_group " + 
                "WHERE at_account_group.acc_id = ? AND at_account_group.grp_id = at_cub_details.grp_id " +
                    "AND at_cub_details.cd_id NOT IN ( " +
                                    "SELECT IFNULL (at_cub_details.cd_id, 0) " +
                                          "FROM at_group, at_account_group group1, at_account_group group2, at_accounts " + 
                                          "LEFT JOIN at_account_cub_association ON at_accounts.acc_id = at_account_cub_association.acc_id " +
                                          "LEFT JOIN at_cub_details ON at_account_cub_association.cd_id = at_cub_details.cd_id " +
                                          "WHERE (at_accounts.acc_id = ? " +
                                            "AND (group1.acc_id = ?  " +
                                            "AND group1.grp_id = group2.grp_id " +
                                            "AND group2.acc_id = at_accounts.acc_id)) " +
                                            "AND (group2.grp_id = at_group.grp_id)) " +
                "ORDER BY at_cub_details.cd_surname, at_cub_details.cd_first_name;");

亲切的问候，

格林

MySQL-仅当成员不在另一个列表中时才返回成员列表

1 个答案: