有sql脚本如下：use kdd99; create table kdd99_accounts ( account_id integer, district_id integer, frequency varchar(20), date DATE ); load data infile 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/kdd99_accounts.csv' into table kdd99_accounts CHARACTER SET gb2312 fields terminated by ',' optionally enclosed by '"' escaped by '"' lines terminated by '\r\n'; create table Kdd99_card( card_id integer, disp_id integer, issued DATE, type varchar(10) ); load data infile 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/Kdd99_card.csv' into table Kdd99_card CHARACTER SET gb2312 fields terminated by ',' optionally enclosed by '"' escaped by '"' lines terminated by '\r\n'; create table Kdd99_disp( disp_id integer, client_id integer, account_id integer, type varchar(6) ); load data infile 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/Kdd99_disp.csv' into table Kdd99_disp CHARACTER SET gb2312 fields terminated by ',' optionally enclosed by '"' escaped by '"' lines terminated by '\r\n'; create table Kdd99_trans( trans_id integer,account_id integer,date date,type varchar(2),operation varchar(20),amount long,balance long,k_symbol varchar(20),bank varchar(4),account long ); load data infile 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/Kdd99_trans.csv' into table Kdd99_trans CHARACTER SET gb2312 fields terminated by ',' optionally enclosed by '"' escaped by '"' lines terminated by '\r\n';请问如何验证客户开通信用卡之后，其账户余额相较于开卡之前是否有提升

要验证客户开通信用卡之后，其账户余额相较于开卡之前是否有提升，可以按照以下步骤进行：

1. 首先，根据Kdd99_card表和Kdd99_disp表中的信息，找到所有开通了信用卡的客户对应的account_id。

2. 然后，根据Kdd99_trans表中的信息，筛选出这些客户在开通信用卡之前和之后的所有交易记录。可以使用以下SQL语句筛选开通信用卡之前的交易记录：

SELECT *
FROM Kdd99_trans
WHERE account_id IN (
    SELECT account_id
    FROM Kdd99_disp
    WHERE disp_id IN (
        SELECT disp_id
        FROM Kdd99_card
        WHERE issued < 开卡日期
    )
);

其中，开卡日期需要替换为实际的开卡日期。

3. 计算开通信用卡之前和之后的账户余额之和，并比较两者的差值。可以使用以下SQL语句计算开通信用卡之前的账户余额之和：

SELECT SUM(balance)
FROM Kdd99_trans
WHERE account_id IN (
    SELECT account_id
    FROM Kdd99_disp
    WHERE disp_id IN (
        SELECT disp_id
        FROM Kdd99_card
        WHERE issued < 开卡日期
    )
);

其中，开卡日期需要替换为实际的开卡日期。

4. 同样地，可以使用以下SQL语句计算开通信用卡之后的账户余额之和：

SELECT SUM(balance)
FROM Kdd99_trans
WHERE account_id IN (
    SELECT account_id
    FROM Kdd99_disp
    WHERE disp_id IN (
        SELECT disp_id
        FROM Kdd99_card
        WHERE issued >= 开卡日期
    )
);

其中，开卡日期需要替换为实际的开卡日期。

5. 最后，比较两个账户余额之和的差值，如果差值为正数，则说明客户开通信用卡之后的账户余额相较于开卡之前有提升。