为什么我的 ORDER BY create_time ASC 变成了 order by ASC

开发是一件“升级打怪”的事，在开发各个环境下，妖怪频出，战术不断升级。程序员想要抛开迷雾，窥得真相，须得先参透个中招式，然后逐一解决。

本期文章的内容“就地取材”，来源自 LigaAI 工作中常见的开发问题，并通过「场景测试—分析区别—提出解决方案」的方法帮我们规避和尽早识别这种陷阱~话不多说，一起来看看吧！

遇到的问题：

“ 两条一毛一样的sql，分页的sql执行没问题，不分页的sql执行就有问题？”

01、场景准备

>> 测试场景

CREATE TABLE `test_page_or_not` (
  `id` bigint(20) NOT NULL COMMENT '主键编号',
  `name` varchar(255) COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '名称',
  `create_time` datetime(3) NOT NULL COMMENT '创建时间',
  `create_by` bigint(20) NOT NULL COMMENT '创建人',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='测试分页与不分页';

INSERT INTO `test_page_or_not` (`id`, `name`, `create_time`, `create_by`) VALUES (1, 'name1', '2022-02-17 22:25:04.000', 0);
INSERT INTO `test_page_or_not` (`id`, `name`, `create_time`, `create_by`) VALUES (2, 'name2', '2022-02-17 22:25:04.000', 0);
INSERT INTO `test_page_or_not` (`id`, `name`, `create_time`, `create_by`) VALUES (3, 'name3', '2022-02-18 22:25:04.000', 0);
INSERT INTO `test_page_or_not` (`id`, `name`, `create_time`, `create_by`) VALUES (4, 'name4', '2022-02-19 22:25:04.000', 0);

一些Java类文件：

public class TestWithPageDTO extends PageDTO {

    private static final long serialVersionUID = -970059691509424681L;

    private String name;

    private String orderBy;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getOrderBy() {
        return orderBy;
    }

    public void setOrderBy(String orderBy) {
        this.orderBy = orderBy;
    }

    @Override
    public String toString() {
        return "TestWithPageDTO{" +
                "name='" + name + '\'' +
                ", orderBy='" + orderBy + '\'' +
                '}';
    }
}


public class PageDTO extends BaseDTO {

    private static final long serialVersionUID = 2572899663737669356L;

    private Integer pageSize = 10;

    private Integer pageNum = 1;

    public Integer getPageSize() {
        return pageSize;
    }

    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }

    public Integer getPageNum() {
        return pageNum;
    }

    public void setPageNum(Integer pageNum) {
        this.pageNum = pageNum;
    }

    @Override
    public String toString() {
        return "PageDTO{" +
                "pageSize=" + pageSize +
                ", pageNum=" + pageNum +
                '}';
    }
}


public class BaseDTO implements Serializable {

    private static final long serialVersionUID = 9055050419546393543L;
}



public class TestWithoutPageDTO extends BaseDTO {

    private static final long serialVersionUID = 7862152821778815456L;

    private String name;

    private String orderBy;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getOrderBy() {
        return orderBy;
    }

    public void setOrderBy(String orderBy) {
        this.orderBy = orderBy;
    }

    @Override
    public String toString() {
        return "TestWithoutPageDTO{" +
                "name='" + name + '\'' +
                ", orderBy='" + orderBy + '\'' +
                '}';
    }
}

>> 分页场景

先来看看分页场景的参数、代码和日志打印，从日志可以看出SQL的最后执行是没有问题的。
请求参数：

{
  "name": "name",
  "orderBy": "ASC"
}

sql文件：

<!--分页查询数据-->
<select id="selectWithPage" parameterType="com.peng.java_study.api.dto.TestWithPageDTO" resultMap="BaseResultMap">
    SELECT * FROM test_page_or_not tpon
    WHERE
        tpon.name LIKE CONCAT("%", #{name, jdbcType=VARCHAR}, "%")
    <if test="orderBy != null and orderBy != ''">
        ORDER BY tpon.create_time ${orderBy}
    </if>
</select>

日志：

2022-02-18 16:39:09.217 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage_COUNT         : ==>  Preparing: SELECT count(0) FROM test_page_or_not tpon WHERE tpon.name LIKE CONCAT("%", ?, "%")
2022-02-18 16:39:09.218 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage_COUNT         : ==> Parameters: name(String)
2022-02-18 16:39:09.234 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage_COUNT         : <==      Total: 1
2022-02-18 16:39:09.236 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage               : ==>  Preparing: SELECT * FROM test_page_or_not tpon WHERE tpon.name LIKE CONCAT("%", ?, "%") ORDER BY tpon.create_time ASC LIMIT ?
2022-02-18 16:39:09.236 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage               : ==> Parameters: name(String), 10(Integer)
2022-02-18 16:39:09.238 DEBUG 18036 --- [nio-8080-exec-3] c.p.j.c.m.T.selectWithPage               : <==      Total: 4

>> 不分页场景

再来看看正常场景的参数、代码和日志打印：从日志可以看出 SQL 的执行报错了，因为 SQL 从 ORDER BY tpon.create_time ASC 变成了 order by ASC。

请求参数：


{
  "name": "name",
  "orderBy": "ASC"
}

sql 文件：


<!--不分页查询数据-->
<select id="selectWithoutPage" parameterType="com.peng.java_study.api.dto.TestWithoutPageDTO" resultMap="BaseResultMap">
    SELECT * FROM test_page_or_not tpon
    WHERE
        tpon.name LIKE CONCAT("%", #{name, jdbcType=VARCHAR}, "%")
    <if test="orderBy != null and orderBy != ''">
        ORDER BY tpon.create_time ${orderBy}
    </if>
</select>

日志:


2022-02-18 16:52:24.684 DEBUG 18036 --- [nio-8080-exec-5] c.p.j.c.m.T.selectWithoutPage            : ==>  Preparing: SELECT * FROM test_page_or_not tpon WHERE tpon.name LIKE CONCAT("%", ?, "%") order by ASC
2022-02-18 16:52:24.684 DEBUG 18036 --- [nio-8080-exec-5] c.p.j.c.m.T.selectWithoutPage            : ==> Parameters: name(String)
2022-02-18 16:52:24.687 ERROR 18036 --- [nio-8080-exec-5] c.p.java_study.rest.test.TestController  : TestController.list(TestWithoutPageDTO) exception: 

org.springframework.jdbc.BadSqlGrammarException: 
### Error querying database.  Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ASC' at line 1
### The error may exist in file [D:\file\project\1\java-study\java-study-provider\target\classes\mapper\TestPageOrNotMapper.xml]
### The error may involve com.peng.java_study.core.mapper.TestPageOrNotMapper.selectWithoutPage-Inline
### The error occurred while setting parameters
### SQL: SELECT * FROM test_page_or_not tpon WHERE tpon.name LIKE CONCAT("%", ?, "%") order by ASC
### Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ASC' at line 1
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ASC' at line 1
        at org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator.doTranslate(SQLErrorCodeSQLExceptionTranslator.java:235) ~[spring-jdbc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72) ~[spring-jdbc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:91) ~[mybatis-spring-2.0.6.jar:2.0.6]
        at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:441) ~[mybatis-spring-2.0.6.jar:2.0.6]
        at com.sun.proxy.$Proxy92.selectList(Unknown Source) ~[na:na]
        at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:224) ~[mybatis-spring-2.0.6.jar:2.0.6]
        at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:147) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:80) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.binding.MapperProxy$PlainMethodInvoker.invoke(MapperProxy.java:152) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:85) ~[mybatis-3.5.6.jar:3.5.6]
        at com.sun.proxy.$Proxy93.selectWithoutPage(Unknown Source) ~[na:na]
        at com.peng.java_study.core.manager.impl.TestPageOrNotManagerImpl.selectWithoutPage(TestPageOrNotManagerImpl.java:36) ~[classes/:na]
        at com.peng.java_study.rest.test.TestController.list(TestController.java:150) ~[classes/:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at com.peng.java_study.config.LanguageFilter.doFilter(LanguageFilter.java:39) ~[classes/:na]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
        at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
Caused by: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ASC' at line 1
        at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120) ~[mysql-connector-java-8.0.23.jar:8.0.23]
        at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.23.jar:8.0.23]
        at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953) ~[mysql-connector-java-8.0.23.jar:8.0.23]
        at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370) ~[mysql-connector-java-8.0.23.jar:8.0.23]
        at com.zaxxer.hikari.pool.ProxyPreparedStatement.execute(ProxyPreparedStatement.java:44) ~[HikariCP-3.4.2.jar:na]
        at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.execute(HikariProxyPreparedStatement.java) ~[HikariCP-3.4.2.jar:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
        at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59) ~[mybatis-3.5.6.jar:3.5.6]
        at com.sun.proxy.$Proxy132.execute(Unknown Source) ~[na:na]
        at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:325) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) ~[mybatis-3.5.6.jar:3.5.6]
        at com.github.pagehelper.util.ExecutorUtil.pageQuery(ExecutorUtil.java:177) ~[pagehelper-5.1.11.jar:na]
        at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:104) ~[pagehelper-5.1.11.jar:na]
        at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.6.jar:3.5.6]
        at com.sun.proxy.$Proxy130.query(Unknown Source) ~[na:na]
        at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147) ~[mybatis-3.5.6.jar:3.5.6]
        at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140) ~[mybatis-3.5.6.jar:3.5.6]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
        at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:427) ~[mybatis-spring-2.0.6.jar:2.0.6]
        ... 62 common frames omitted

02、分析

两个 sql 的语句和入参是一毛一样的，唯一的区别在于一个使用了分页，另一个没有使用分页。因此我们来仔细分析下报错日志，查找 sql 被修改的原因。

>> 分析具体的代码调用链

在日志的99行，我们发现有一个 PageHelper 的调用栈。

 at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:104) ~[pagehelper-5.1.11.jar:na]

进入该行代码，发现它进入了分页查询。问题来了：

明明我们使用的对象是 TestWithoutPageDTO.class，调用的 sql 也是 selectWithoutPage，为啥还是会进入分页查询呢？

让我们来一探究竟：

下图的1号红色圈可以帮助我们判断当前sql是否需要进行分页。根据图数据显示，本应该走 else 的分支（不分页，3号绿色圈）的，但最后进了 if 分支（分页，2号红色圈）。

继续使用 skip 方法查看。按照该代码的逻辑，4号红色圈的 page 应为 null 才不会分页；既然分页了，那就说明 page 不为 null 。
利用 getPage 方法，在经过调试后我们发现，代码进入了5号红色圈位置。这表明，要么，参数对象已实现了 IPage 接口，要么，supportMethodsArguments 参数为 true。

根据上面 sql 参数，我们得知参数是 TestWithoutPageDTO.class 的实例，它的类继承图如下。该类并没有继承或实现 IPage 接口，因此肯定是 supportMethodsArguments 参数为 true 。

进入PageHelper官网，查看 supportMethodsArguments 参数介绍：根据参数对象中的属性自动识别是否需要分页。

再查看当前项目的配置，发现当前项目确实配置了该参数，既然它确实可以简化一些操作，那这个属性还不能改动。


supportMethodsArguments：支持通过 Mapper 接口参数来传递分页参数，默认值false，分页插件会从查询方法的参数值中，自动根据上面 params 配置的字段中取值，查找到合适的值时就会自动分页。使用方法可以参考测试代码中的 com.github.pagehelper.test.basic 包下的 ArgumentsMapTest 和 ArgumentsObjTest。

pagehelper:
  helperDialect: mysql
  reasonable: true
  supportMethodsArguments: true
  params: count=countSql

继续进入5号红色圈内部的 getPageFromObject 方法，重点看一下13号黄色圈，这个圈使用反射的方式去获取参数对象的orderBy属性。

很快，问题找到了：

笔者为了排序在实体中增加了 orderBy 属性，因此 hasOrderBy 为 true；进入9号红色圈的代码块后，创建了分页的对象，导致 PageHelper 插件把该 sql 语句作为分页查询来对待，自然也就把ORDER BY create_time ASC 语句偷梁换柱了。

找出问题所在，接下来就是解决了。

03、解决

>> 方案一：

将 supportMethodsArguments 属性改为 false ，但这个改动很有可能会对现有的sql查询语句造成一定的影响，因此不推荐。

pagehelper:
  helperDialect: mysql
  reasonable: true
  supportMethodsArguments: false
  params: count=countSql

>> 方案二：

将实体类中的 orderBy 改为另一个变量名，比如 orderByCreateTime ，这样就可以避免 PageHelper 认错分页参数了。

public class TestWithoutPageDTO extends BaseDTO {

    private static final long serialVersionUID = 7862152821778815456L;

    private String name;

    private String orderByCreateTime;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getOrderByCreateTime() {
        return orderByCreateTime;
    }

    public void setOrderByCreateTime(String orderByCreateTime) {
        this.orderByCreateTime = orderByCreateTime;
    }

    @Override
    public String toString() {
        return "TestWithoutPageDTO{" +
                "name='" + name + '\'' +
                ", orderByCreateTime='" + orderByCreateTime + '\'' +
                '}';
    }
}


<!--不分页查询数据-->
<select id="selectWithoutPage" parameterType="com.peng.java_study.api.dto.TestWithoutPageDTO" resultMap="BaseResultMap">
    SELECT * FROM test_page_or_not tpon
    WHERE
        tpon.name LIKE CONCAT("%", #{name, jdbcType=VARCHAR}, "%")
    <if test="orderByCreateTime != null and orderByCreateTime != ''">
        ORDER BY tpon.create_time ${orderByCreateTime}
    </if>
</select>

修改后的日志，无异常产生：

2022-02-18 21:00:58.928 DEBUG 9768 --- [nio-8080-exec-1] c.p.j.c.m.T.selectWithoutPage            : ==>  Preparing: SELECT * FROM test_page_or_not tpon WHERE tpon.name LIKE CONCAT("%", ?, "%") ORDER BY tpon.create_time ASC
2022-02-18 21:00:58.944 DEBUG 9768 --- [nio-8080-exec-1] c.p.j.c.m.T.selectWithoutPage            : ==> Parameters: name(String)
2022-02-18 21:00:58.960 DEBUG 9768 --- [nio-8080-exec-1] c.p.j.c.m.T.selectWithoutPage

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本文作者：rookie0peng

为什么我的 ORDER BY create_time ASC 变成了 order by ASC

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为什么我的 ORDER BY create_time ASC 变成了 order by ASC

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01、场景准备