从两个表中选择数据，mysql

我的数据库有两个表customer和transaction

customer表有8列，transaction表有4列

客户表主键是id，在事务表中没有主键，每个客户在事务表中存在多条记录

我需要从customer中选择4列，从transaction中选择3列

以下是查询：

query ='SELECT c.customer_id AS "Customer ID",
               c.father_name AS "Father Name",
               c.address AS Address,
               c.phone_number AS "Phone Number",
               c.mobile_number AS "Mobile Number",
               c.id_proof AS "ID Proof",
               c.area AS "Area",
               c.ip_address AS "IP Address",
               c.mac_address AS "MAC Address",
               c.package_type AS "Package Type",
               c.name AS Name,
               c.activation_date AS "Activation Date",
               c.status AS "Status",
               c.installation_cost AS "Installation Cost",
               c.totalamount_paid AS "Total Amount Paid",
               c.monthly_amount AS "Monthly Amount",
               c.lastpaid_date AS "Last Paid Date",
               c.lastpaid_amount AS "Last Paid Amount",
               c.nextpay_date AS "Next Pay Date",
               c.totaldue_amount AS "Total Due Amount",
               t.agent_id AS "Agent ID",
               t.token_number AS "Token Number",
               t.machine_id AS "Machine ID"
          FROM customer c INNER JOIN transaction t ON c.customer_id = t.customer_id
        WHERE DATE(t.paid_date)BETWEEN '" + fromDate + "'AND '" + toDate + "' ";

但问题是：

记录在事务表中存在多少次，这些次是它的给定记录，但我只需要一次

我该怎么做呢？

试试这个-

query = " ... ... ... GROUP BY c.customer_id";

---

您很可能希望对某些列求和或使用其他聚合函数。

问题在于您的查询逻辑。您可以从

transaction

表中选择三列。现在，对于一个客户，可以有多个交易。如果您正在选择

t.agent\u id

、

t.token\u number

和

t.machine\u id

，这将为您提供客户进行的每笔交易的这些值

如果您的业务逻辑允许，请从

select

列表中删除这三列，并使用

EXISTS

子句，而不是

内部联接，如下所示：

query ='SELECT c.customer_id AS "Customer ID",
               c.father_name AS "Father Name",
               c.address AS Address,
               c.phone_number AS "Phone Number",
               c.mobile_number AS "Mobile Number",
               c.id_proof AS "ID Proof",
               c.area AS "Area",
               c.ip_address AS "IP Address",
               c.mac_address AS "MAC Address",
               c.package_type AS "Package Type",
               c.name AS Name,
               c.activation_date AS "Activation Date",
               c.status AS "Status",
               c.installation_cost AS "Installation Cost",
               c.totalamount_paid AS "Total Amount Paid",
               c.monthly_amount AS "Monthly Amount",
               c.lastpaid_date AS "Last Paid Date",
               c.lastpaid_amount AS "Last Paid Amount",
               c.nextpay_date AS "Next Pay Date",
               c.totaldue_amount AS "Total Due Amount" /*,
               t.agent_id AS "Agent ID",
               t.token_number AS "Token Number",
               t.machine_id AS "Machine ID" -- */
          FROM customer c 
        WHERE EXISTS (SELECT 1
                        FROM transaction t
                       WHERE c.customer_id = t.customer_id
                         AND DATE(t.paid_date)BETWEEN '"
                                                        + fromDate
                                                        + "'AND '"
                                                        + toDate + "' "

现在，如果您的企业确实需要这三个值，您可以简单地使用
选择DISTINCT
，不再担心重复值。
query='SELECT c.customer\u id作为“customer id”，
c、 父亲的名字是“父亲的名字”，
c、 地址作为地址，
c、 电话号码为“电话号码”，
c、 手机号码为“手机号码”，
c、 身份证明为“身份证明”，
c、 面积为“面积”，
c、 ip_地址为“ip地址”，
c、 mac_地址作为“mac地址”，
c、 包装类型为“包装类型”，
c、 姓名作为姓名，
c、 激活日期为“激活日期”，
c、 状态为“状态”，
c、 安装成本作为“安装成本”，
c、 支付的总金额作为“支付的总金额”，
c、 每月金额为“每月金额”，
c、 lastpaid_日期为“Last Paid date”，
c、 上次支付金额为“上次支付金额”，
c、 下一个付款日期为“下一个付款日期”，
c、 总到期金额作为“总到期金额”，
t、 代理id为“代理id”，
t、 令牌号作为“令牌号”，
t、 机器id为“机器id”
从客户c内部连接事务t到c.customer\u id=t.customer\u id
其中日期（t.paid_DATE）介于“+fromDate+”和“+toDate+”之间
GROUP BY c.customer_id；
会限制1个适合您的需求吗？我可以在查询中保留在哪里为什么不使用
DISTINCT
？不是这样，它只给出第一条记录，我只希望每个客户有一条记录。我正在开发.net应用程序，我是否应该在上面的查询之后使用GROUP BY.if（reportsmachine.Text！=“”）{query=query+”和“+”t.machine_id=“+””“+reportsmachine.Text+”；}如果（reportscustomer.Text！=”）{query=query+”和“+”t.customer_id=“+”“+reportscustomer.Text+”；}这里有reportscustomer和reportsmachine是文本框。@SahilMittal-好吧，看来我比你早7分钟回答了这个问题，你刚刚编辑了你的答案，使之与我的相似。因此，如果它是正确的，我的答案就是被接受。提示：）在哪里使用DISTINCT in querySimple-ext to
SELECT
，如
query='SELECT DISTINCT c.customer\u id…
。您看起来对SQL很陌生。我建议你多做些家庭作业。转到w3schools.com的SQL教程。
query ='SELECT c.customer_id AS "Customer ID",
               c.father_name AS "Father Name",
               c.address AS Address,
               c.phone_number AS "Phone Number",
               c.mobile_number AS "Mobile Number",
               c.id_proof AS "ID Proof",
               c.area AS "Area",
               c.ip_address AS "IP Address",
               c.mac_address AS "MAC Address",
               c.package_type AS "Package Type",
               c.name AS Name,
               c.activation_date AS "Activation Date",
               c.status AS "Status",
               c.installation_cost AS "Installation Cost",
               c.totalamount_paid AS "Total Amount Paid",
               c.monthly_amount AS "Monthly Amount",
               c.lastpaid_date AS "Last Paid Date",
               c.lastpaid_amount AS "Last Paid Amount",
               c.nextpay_date AS "Next Pay Date",
               c.totaldue_amount AS "Total Due Amount" /*,
               t.agent_id AS "Agent ID",
               t.token_number AS "Token Number",
               t.machine_id AS "Machine ID" -- */
          FROM customer c 
        WHERE EXISTS (SELECT 1
                        FROM transaction t
                       WHERE c.customer_id = t.customer_id
                         AND DATE(t.paid_date)BETWEEN '"
                                                        + fromDate
                                                        + "'AND '"
                                                        + toDate + "' "