在使用JDBC的時候,有一句SQL是這麼寫的:insert into user_login (username, password, telephone) values (?,?,?);
,可是報錯:
java.sql.SQLException: Field ‘user_id’ doesn’t have a default value
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1092)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1040)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeLargeUpdate(ClientPreparedStatement.java:1347)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdate(ClientPreparedStatement.java:1025)
at com.xxx.login.dao.UserDaoImpl.addUser(UserDaoImpl.java:29)
at com.xxx.login.service.UserServiceImpl.register(UserServiceImpl.java:30)
at com.xxx.login.servlet.RegisterServlet.doGet(RegisterServlet.java:23)
at com.xxx.login.servlet.RegisterServlet.doPost(RegisterServlet.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.base/java.lang.Thread.run(Thread.java:834)
單獨回到命令行進行insert測試,發現錯誤原因是沒有默認值。
之後又嘗試了alter table user_login alter user_id set default 10005;
,這種附加default的方式被證實在第二次插值的時候會因爲主鍵不允許重複值而報錯,所以不可行。
那我們可以考慮加入auto_increment:alter table user_login auto_increment=1;
,執行後得到Query OK, 0 rows affected
,但還是不能解決問題,有和沒有一樣。
當然了,我們稍加分析可知default與primary_key是不兼容的,所以要去掉,此時使用desc user_login;
命令查詢表結構,如下圖:
果然是因爲auto_increment看似加進去實則沒加進去導致的。
那問題就在於怎麼加這個auto_increment?
我們直接alter是無效的,而刪表並重建,是不現實的。
似乎很糾結、很困難,下面說一下怎麼寫命令:
alter table user_login modify column `user_id` int not null auto_increment;
如果我們這麼處理的話,除了主鍵以外把整列重新指定,就能解決問題:
一定不要再附帶primary_key,只因爲主鍵已經被指定。
驗證:
mysql> insert into user_login (username, password, telephone) values('XiaoLaJiao', '12123', '12123');
Query OK, 1 row affected (0.15 sec)
mysql> insert into user_login (username, password, telephone) values('XiaoCaiJi', '12123', '12123');
Query OK, 1 row affected (0.14 sec)
再開一下Navicat,證明確實insert成功,這樣我們就化解了這個問題。
更多情況,請戳此處!
文中講解了三種情況如何去處理,比本文覆蓋面更廣;本文勝在詳細和覆盤各種嘗試過程。