假设这种结构是正确的：

MariaDB [test]> SELECT * FROM `Users`;
+----------+---------+------------+
| username | zipcode | birthdate  |
+----------+---------+------------+
| tester55 |   72758 | 1999-09-09 |
| tester86 |   60608 | 1983-05-10 |
| iosuser1 |   10011 | 1975-12-19 |
| iosuser5 |   10011 | 1975-12-21 |
+----------+---------+------------+
4 rows in set (0.00 sec)

和

MariaDB [test]> SELECT * FROM `Blocks`;
+----------+-------------+
| blocker  | blockeduser |
+----------+-------------+
| tester86 | tester55    |
| iosuser5 | tester55    |
+----------+-------------+
2 rows in set (0.00 sec)

您可以使用以下查询：

MariaDB [test]> SELECT `Users`.* FROM `Users` LEFT JOIN `Blocks` ON `Users`.`username` = `Blocks`.`blocker` WHERE `Blocks`.`blocker` IS NULL;
+----------+---------+------------+
| username | zipcode | birthdate  |
+----------+---------+------------+
| tester55 |   72758 | 1999-09-09 |
| iosuser1 |   10011 | 1975-12-19 |
+----------+---------+------------+
2 rows in set (0.00 sec)

您所说的表具有完全不同的结构是没有必要的，这就是数据库的全部概念。您可以使用@emaniazevedo建议的左连接，但需要根据需要检查这两列，或者使用notexists。
我宁愿不存在，因为我认为它更清楚。

select * from users 
where not exists(
    select * from blocks where Users.username = Blocks.blocker or users.username=Blocks.blockeduser
)

edit：由于您现在已经添加了您的查询，这个notexists应该只是作为一个附加子句，用and来添加子句。我也不明白你为什么要用having，我想那也应该是and。
第二次编辑：这是删除了混淆括号的整个查询。它现在从查找用户开始，在同一个zip中查找所有其他用户，然后查找所有其他匹配的用户。可以使用别名用户表来执行此操作，而不必使用嵌套查询。
顺便说一句，它会检查用户是否在阻止程序表的任一侧-如果不正确，则相应地修改。

select * from (
SELECT  zipcodes.zip, zipcodes.city, zipcodes.state,
        users.id, users.username, users.ava, users.gender, users.race, users.headline, users.marital, users.height, users.bodytype, users.religion, users.education, 
        users.occupation, users.politics, users.kids, users.wantkids, users.favdrink, users.drink, users.smoke, users.interests, users.aboutme, users.seekingGender, 
        users.seekingdistance, users.seekingrace, users.seekingmarital, users.seekingminage, users.seekingmaxage, users.seekingminheight, users.seekingmaxheight, 
        users.seekingbodytype, users.seekingreligion, users.seekingeducation, users.seekingoccupation, users.seekingpolitics, users.seekingkids, users.seekingwantkids, 
        users.seekingdrink, users.seekingsmoke, users.birthdate, 
        YEAR(CURRENT_TIMESTAMP) - YEAR(users.birthdate) - (RIGHT(CURRENT_TIMESTAMP, 5) < RIGHT(users.birthdate, 5)) as age, 
        3959 * acos(cos(radians(zipcodes.latitude)) *
                cos(radians(center.latitude)) *
                cos(radians(zipcodes.longitude ) -
                    radians(center.longitude)) +
                sin(radians(zipcodes.latitude)) *
                sin(radians(center.latitude))) AS distance 
from users as seeker
join zipcodes as centre on centre.zip=seeker.zip
JOIN users ON seeker.zip = users.zip
join zipcodes on zipcodes.zip=users.zip
where seeker.username = 'tester55' and seeker.username<>users.username AND users.gender = seeker.seekingGender AND seeker.gender=users.seekingGender
    AND users.seekingmarital LIKE seeker.seekingmarital AND users.bodytype LIKE seeker.seekingbodytype AND users.religion LIKE seeker.seekingreligion 
    AND users.education LIKE seeker.seekingducation and users.occupation LIKE seeker.seekingoccupation AND users.politics LIKE seeker.seekingpolitics 
    AND users.kids LIKE seeker.seekingkids AND users.wantkids LIKE seeker.seekingwantkids AND users.drink LIKE seeker.seekingdrinker 
    AND users.smoke LIKE seeker.seekingsmoker AND users.race LIKE seeker.seekingrace AND seeker.seekingminheight <= users.height AND seeker.seekingmaxheight >= users.height 
    AND users.birthdate >= DATE_SUB(NOW(), INTERVAL seeker.seekingmaxage YEAR) AND users.birthdate <= DATE_SUB(NOW(), INTERVAL seeker.seekingminage YEAR)
    and not exists(
        select * from blocks where blocks.blocker=users.username and blocks.blockeduser=seeker.username
    )
) selections
where distance < selections.seekingdistance
ORDER BY distance

edit：使用原始示例数据（包括表def和insert）对上述内容进行简化的版本。我将所有示例用户更新为相同的zip，并将其作为唯一标准。如果这对您不起作用，请确保被阻止的用户确实正确匹配-例如没有尾随空格。

create table users (username varchar(20),zipcode varchar(10),birthdate date)
insert users values ('tester55','10011','1999-09-09')
,('tester86','10011','1983-05-10')
,('iosuser1','10011','1975-12-19')
,('iosuser5','10011','1975-12-21')
,('tester150','10011','1975-12-21')

create table Blocks(blocker varchar(20),blockeduser varchar(20))
insert Blocks values ('tester86','tester55'),('iosuser5','tester55'),('tester150','tester55')

create table ZipCode(zipcode varchar(10), city varchar(20))
insert zipcode values ('72758','Rogers'),('60608','Chicago')

select users.*
from users seeker
join users on users.zipcode=seeker.zipcode and users.username<>seeker.username
where seeker.username='tester55'
and not exists(select * from blocks where blocks.blocker=users.username and blocks.blockeduser=seeker.username)

结果：（已排除阻止tester55的所有用户）

username    zipcode birthdate
iosuser1    10011   1975-12-19