MySQL连接-没有结果

Question

我很确定这与我选择的表或联接的顺序有关，但是在我的查询中尝试了各种重新排序之后，我仍然坚持0的结果。

有人能给我指明正确的方向吗？

表A(返回355个结果)：

SELECT DISTINCT
    person.person_id as "Person ID",
    CONCAT(person.last, ', ', person.first) as "Patient Name",
    person.birthday as "Birthday",
    person_ins_tie.insurance_id as "Insurance ID",
    insurance.carrier as "Carrier",
    insurance.phone as "Carrier Phone Number"
FROM
    person
        JOIN
    person_ins_tie ON person.person_id = person_ins_tie.person_id
        JOIN
    insurance ON person_ins_tie.insurance_id = insurance.insurance_id
WHERE
    insurance.carrier LIKE 'Blue%'

表B(返回0结果/没有错误)：

SELECT DISTINCT
    person.person_id as 'Person ID',
    patient.display_id as 'Chart #',
    CONCAT(person.last, ', ', person.first) as 'Patient Name',
    person.birthday as 'Birthday',
    insurance.insurance_id as 'Insurance ID',
    insurance.carrier as 'Carrier',
    insurance.phone as 'Carrier Phone Number'
FROM
    person
        JOIN
    person_ins_tie ON person.person_id = person_ins_tie.person_id
        JOIN
    insurance ON person_ins_tie.insurance_id = insurance.insurance_id
        JOIN
    patient ON person.person_id = patient.person_id
WHERE
    insurance.carrier LIKE 'Blue%'

我很感谢你的反馈！

Answer 1

JOIN的意思是INNER JOIN。

在本例中，当您加入patient表时，它尝试在person_id of patient表中从person表中找到person_id。因此，这里唯一的可能是在person_id表的person_id列中找不到来自上一个联接集的person_id。所以记录是0！