数据库系统原理与实践——修复第四次作业中的错误

原先的表达式含义是只能购买RS或CS而没买别的，新的含义才是同时购买RS和CS。

数据库系统原理与实践/平时作业/第四次作业.tex

@@ -198,16 +198,17 @@ from (select account.ACCOUNT_ID, OPEN_BRANCH_ID, AVAIL_BALANCE, max_avail_balanc
         \begin{minted}{SQL}
 select individual.ID_NUMBER 身份证号, concat(individual.LAST_NAME, individual.FIRST_NAME) 姓名全名
 from individual
-where not exists(select *
-                    from account
-                    where PRODUCT_CD != 'CS' and PRODUCT_CD != 'RS' and account.CUST_ID = individual.CUST_ID);
+where not not exists(select * from account where PRODUCT_CD = 'CS' and account.CUST_ID = individual.CUST_ID)
+  and not not exists(select * from account where PRODUCT_CD = 'RS' and account.CUST_ID = individual.CUST_ID);
         \end{minted}
         \begin{csv}
 ,身份证号,姓名全名
-1,41032619780815564X,许文强
-2,370900196802069281,何婕
-3,320623197108259227,施珊珊
-4,321111197703197600,孔庆东
+1,350403198204222299,尤青
+2,41032619780815564X,许文强
+3,370900196802069281,何婕
+4,450881196612220768,吕东
+5,320623197806169227,严匡
+6,320623197108259227,施珊珊
         \end{csv}
     }