php - UNION SELECT mysql php pdo 无值返回

Question

SELECT t1.case_num AS casenum, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL
FROM luponcase_tbl t1
WHERE t1.case_num = :id AND t1.status = :active
UNION
SELECT mhearing_number, mhearing_status, mhearing_number, NULL, NULL, NULL, NULL, NULL,
    NULL, NULL
FROM luponcase_mediation_tbl t4
WHERE t4.case_num = :id AND t4.status = :active
UNION
SELECT mfileblob, mfile_type, mfilesize, mhearing_number, mnameoffile, NULL, NULL, NULL,
    NULL, NULL
FROM luponcase_mediation_reference_tbl t5
WHERE t5.case_num = :id AND t5.status = :active

这是我的 union sql，我没有得到结果，所以我试图回显结果

while ($selected_row = $stmt->fetch(PDO::FETCH_ASSOC)) {
                        print_r($selected_row);
} 

令我惊讶的是结果是

Array ( [casenum] => 14 [NULL] => ) 

我假设第一个值是正确的，然后 NULL 列不是。如何以一种方式使我只获得除 NULL 列之外的列。

Answer 1

当你连接到数据库时，你可以设置一些属性来控制PDO如何处理数据库查询返回的Nulls和Empty Strings