MySQL查询，比较表reseults

Question

当我单独执行这些查询，我得到下面$sql1->first 2列，$sql2->second 2列结果：

$userid='AD0004'; 
$comp_code='AD'; 

$sql1 = "SELECT DISTINCT CCCOMPANY, CCCNTY 
     FROM D.TMTBCNTC 
     WHERE CCCOMPANY='$comp_code'"; 

// //gets USER & their counties 
$sql2 = "SELECT DISTINCT UCCOMPANY, UCCNTY 
     FROM D.TMTBCNTU 
     WHERE UCUSERID='$userid' 
     AND UCCOMPANY='$comp_code'"; 

CCCOMPANY CCCNTY UCCNTY UCCOMPANY 
AD  AT    
AD  BB  BB  AD 
AD  BE  BE  AD 
AD  BR  BR  AD 
AD  CM  CM  AD 
AD  CO  CO  AD 
AD  DE  DE  AD 
AD  EB  EB  AD 
AD  EP  EP  AD 
AD  FB  FB  AD 
AD  GB    
AD  GU  GU  AD 
AD  GV  GV  AD 
AD  HA  HA  AD 
AD  KF  KF  AD 
AD  KN  KN  AD 
AD  MB  MB  AD 
AD  MG  MG  AD 
AD  PF  PF  AD 
AD  TA  TA  AD 
AD  UB  UB  AD 
AD  WI  WI  AD 

我想要做的就是加入了列CCCOMPANY=UCCOMPANY && CCCNTY=UCCNTY并返回没有找到匹配项时为空白字段。

我遇到的问题是查询似乎环回通过本身，这意味着我得到每家公司22个县，每个用户20个县，其中就出来20x22 => 440分的结果，我想22分的结果和一个查询。

EDIT1：

$sql = " 
SELECT DISTINCT c_t.CCCOMPANY, c_t.CCCNTY, (
CASE WHEN u_t.UCUSERID='$userid' 
THEN 'exists here' 
END 
) AS UserOnSite 
FROM D.TMTBCNTC as c_t 
LEFT JOIN D.TMTBCNTU AS u_t ON u_t.UCCOMPANY = c_t.CCCOMPANY 
WHERE c_t.CCCOMPANY = '$comp_code'"; 

输出：

AD | AT | 
    AD | BB | 
    AD | BE | 
    AD | BR | 
    AD | CM | 
    AD | CO | 
    AD | DE | 
    AD | EB | 
    AD | EP | 
    AD | FB | 
    AD | GB | 
    AD | GU | 
    AD | GV | 
    AD | HA | 
    AD | KF | 
    AD | KN | 
    AD | MB | 
    AD | MG | 
    AD | PF | 
    AD | TA | 
    AD | UB | 
    AD | WI | 
    AD | AT | exists here 
    AD | BB | exists here 
    AD | BE | exists here 
    AD | BR | exists here 
    AD | CM | exists here 
    AD | CO | exists here 
    AD | DE | exists here 
    AD | EB | exists here 
    AD | EP | exists here 
    AD | FB | exists here 
    AD | GB | exists here 
    AD | GU | exists here 
    AD | GV | exists here 
    AD | HA | exists here 
    AD | KF | exists here 
    AD | KN | exists here 
    AD | MB | exists here 
    AD | MG | exists here 
    AD | PF | exists here 
    AD | TA | exists here 
    AD | UB | exists here 
    AD | WI | exists here 

EDIT2：

$sql = " 
SELECT DISTINCT c_t.CCCOMPANY, c_t.CCCNTY, (
    CASE WHEN u_t.UCUSERID='$userid' 
    THEN 'exists here' 
    END 
    ) AS UserOnSite 
FROM D.TMTBCNTC as c_t 
LEFT JOIN D.TMTBCNTU 
    AS u_t 
    ON u_t.UCCOMPANY = c_t.CCCOMPANY 
WHERE c_t.CCCOMPANY = '$comp_code' 
    AND u_t.UCCNTY = c_t.CCCNTY"; 


    AD | AT | 
    AD | BB | exists here 
    AD | BB | 
    AD | BE | exists here 
    AD | BE | 
    AD | BR | exists here 
    AD | BR | 
    AD | CM | exists here 
    AD | CM | 
    AD | CO | exists here 
    AD | CO | 
    AD | DE | exists here 
    AD | DE | 
    AD | EB | exists here 
    AD | EB | 
    AD | EP | exists here 
    AD | EP | 
    AD | FB | exists here 
    AD | FB | 
    AD | GB | 
    AD | GU | exists here 
    AD | GU | 
    AD | GV | exists here 
    AD | GV | 
    AD | HA | exists here 
    AD | HA | 
    AD | KF | exists here 
    AD | KF | 
    AD | KN | exists here 
    AD | KN | 
    AD | MB | exists here 
    AD | MB | 
    AD | MG | exists here 
    AD | MG | 
    AD | PF | exists here 
    AD | PF | 
    AD | TA | exists here 
    AD | TA | 
    AD | UB | exists here 
    AD | UB | 
    AD | WI | exists here 
    AD | WI | 

Answer 1

尝试此查询：

$sql = " 
SELECT DISTINCT c_t.CCCOMPANY, c_t.CCCNTY, (
CASE WHEN u_t.UCUSERID='$userid' 
THEN 'exists here' 
END 
) AS UserOnSite 
FROM D.TMTBCNTC as c_t 
LEFT JOIN D.TMTBCNTU AS u_t ON u_t.UCCOMPANY = c_t.CCCOMPANY 
WHERE c_t.CCCOMPANY = '$comp_code' 
AND u_t.UCCNTY = c_t.CCCNTY "; // additional where clause 

你命名列和表中并没有真正使得它更容易。但是这应该给你你正在寻找

这应该输出如下结果：

CCCOMPANY CCCNTY UserOnSite 
AD  | AT | NULL    
AD  | BB | exist here 
AD  | BE | exist here 
AD  | BR | exist here 
AD  | CM | exist here 
AD  | CO | exist here 
AD  | DE | exist here 
AD  | EB | exist here 
AD  | EP | exist here 
AD  | FB | exist here 

其次更好的尝试：编辑

$sql = " 
SELECT DISTINCT c.CCCOMPANY, c.CCCNTY, (
SELECT (
    CASE WHEN u.UCUSERID='$userid' 
    THEN 'exists here' 
    END 
) 
FROM D.TMTBCNTU as u 
WHERE u.UCUSERID = '$userid' 
AND u.UCCOMPANY = c.CCCOMPANY 
AND u.UCCNTY = c.CCCNTY 
LIMIT 1 
) AS UserOnSite 
FROM D.TMTBCNTC AS c 
WHERE c.CCCOMPANY = '$comp_code'"; 

这应该更好地工作