MySQL子查询返回空

Question

嗨，我是一个初学者，我正在尝试使子查询的所有结果行都为null，以返回0而不为null。 但我遇到一个错误。 我将非常感谢任何建议。 谢谢

错误代码：1064您的SQL语法错误； 检查与您的MySQL服务器版本相对应的手册，以在'AS'Income'附近使用正确的语法

SELECT  

 COUNT(DISTINCT t1.id) AS 'Val1',


     COALESCE((SELECT SUM(CAST(COALESCE(r.t_payment_total,0) AS DECIMAL(18,2))) AS 'Income'
FROM reserv r
INNER JOIN newtbladds1 t ON t.t_parent_id = r.id
 WHERE r.t_status!="Pending" && r.t_status!="Booked" AND r.c_mid = m.id AND  t.t_type_id = t1.t_type_id 
 ),0)AS 'Income'



 FROM tbladds1 t1
JOIN tbladds1_type tt ON tt.id = t1.t_type_id
JOIN tbladdress m ON m.id = t1.t_mid
JOIN tbladdressfr mf ON mf.id = t1.t_floor_id
JOIN tblppl mp ON mp.t_mid = m.id AND mp.t_type = 'try' AND mp.t_system_id = 'ok'
GROUP BY t1.t_tool_type_id
ORDER BY m.t_m ASC, tt.t_ttype ASC, mf.t_floor ASC;

输出我删除了COALESCE我为空

Val1           Income
10              Null
2               30
23              10
5               Null

期望的输出

Val1           Income
10              0
2               30
23              10
5               0

Answer 1

我建议将子查询移至from子句

SELECT
    t1.t_tool_type_id
  , COUNT( DISTINCT t1.id ) AS `Val1`
  , COALESCE(i.Income , 0 ) AS `Income`
FROM tbladds1 t1
JOIN tbladds1_type tt ON tt.id = t1.t_type_id
JOIN tbladdress m ON m.id = t1.t_mid
JOIN tbladdressfr mf ON mf.id = t1.t_floor_id
JOIN tblppl mp ON mp.t_mid = m.id
    AND mp.t_type = 'try'
    AND mp.t_system_id = 'ok'
left join (
        SELECT
             CAST( SUM(r.t_payment_total) AS decimal(18, 2) ) AS `Income`
        FROM reserv r
        INNER JOIN newtbladds1 t ON t.t_parent_id = r.id
        WHERE r.t_status != 'Pending'
        AND r.t_status != 'Booked'
        AND r.c_mid = m.id
        GROUP BY
            t.t_type_id
    ) as i on t1.t_type_id = i.t_type_id
GROUP BY
    t1.t_tool_type_id
;

nb：我假设r.t_payment_total是数字。

我还建议您始终将单引号用于值/文字，并在MySQL反引号中使用标识（例如列标题），但实际上它们在此查询中不是必需的。