dept40_fk 和 dept60_pk 是级联约束，这里级联禁用后:两个都禁用了。

然后使用启用的命令：

但是却只启用了一个：这里60启用了，但是40没有启用

我看了一下和我遇到相同问题的问答：我在禁用和启用之间并没有对数据库进行过操作。但依然没有自己恢复之间的约束。

请问老师：在视频里

drop table dept90;

只删除了一个表，如果我要一次删除多个表应该怎么写。

请问老师，这里只说了定义唯一性约束，如果我要取消掉这个唯一性约束应该怎么写语句呢？

百度上给的方法是：

Alter table 表名
drop constraint 约束名;

但如果这名字是默认的，我并不清楚该怎么办。

老师，我的plsol是从官网上下载的，是因为这个原因吗？

前段时间数据库用得好好的，今天数据就丢失了，请问如何怎么解决呢

老师，他总是显示错误，怎么回事呢？？？？？

4.12创建一个混合查询显示工作岗位和工作岗位的薪水合计，并且合计部门 20、50、80 和 90 的工作岗位的薪水。给每列一个恰当的列标题。

    按照视频里的语句运行结果是这样的：

    但题目要显示的是部门号为20、50、80 和 90 的全部岗位的合计薪水的话：就要按照department_id分组

select department_id,sum(salary),sum(decode(department_id, 20,salary))"Dep 20",sum(decode(department_id,50,salary))"Dep 50" from employees group by  department_id;

    然后这里就遇到问题了：如果按job_id分组那么 部门的合计薪水就会分开显示（19000拆成了13000和6000，图1），按照department_id分组的话，就没法显示工作岗位（图2）。

    请问老师要做到即显示工作岗位也显示部门的合计薪水(而不是岗位的合计薪水)，语句应该怎么写。

老师这是什么情况

百度找了好久 也没弄好，不行了

老师，我运行出来的结果怎么是0啊

老师我这里哪里出错了，找了半天不知道什么原因

老师：

    问题1：第一条语句可以搜索到，但是改成 ‘%2005’后一条都搜不到。

select last_name, hire_date from employees where hire_date like '%05';
select last_name, hire_date from employees where hire_date like '%2005';

    问题2：第一条语句可以匹配到一条，把 = 改成 like 后一条都没有，并且第三条语句的 '_7-8月-2005' 表示一个占位符的话应该也能匹配到一吧，但是却一个都匹配不到。

select last_name, hire_date from employees where hire_date = '17-8月-2005';
select last_name, hire_date from employees where hire_date like '17-8月-2005';
select  last_name,  hire_date  from  employees  where  hire_date  like  '_7-8月-2005';

实际运算时的情况如下：

SQL>  select last_name, hire_date from employees where hire_date like '%05';
LAST_NAME                 HIRE_DATE
------------------------- -----------
Kochhar                   2005/9/21
Austin                    2005/6/25
Chen                      2005/9/28
Sciarra                   2005/9/30
Baida                     2005/12/24
Tobias                    2005/7/24
Fripp                     2005/4/10
Vollman                   2005/10/10
Nayer                     2005/7/16
Bissot                    2005/8/20
Atkinson                  2005/10/30
Marlow                    2005/2/16
Stiles                    2005/10/26
Davies                    2005/1/29
Partners                  2005/1/5
Errazuriz                 2005/3/10
Tucker                    2005/1/30
Bernstein                 2005/3/24
Hall                      2005/8/20
Smith                     2005/3/10
LAST_NAME                 HIRE_DATE
------------------------- -----------
Doran                     2005/12/15
Vishney                   2005/11/11
Ozer                      2005/3/11
Hutton                    2005/3/19
Bull                      2005/2/20
Chung                     2005/6/14
Dilly                     2005/8/13
Everett                   2005/3/3
Fay                       2005/8/17
29 rows selected

SQL>  select last_name, hire_date from employees where hire_date like '%2005';
LAST_NAME                 HIRE_DATE
------------------------- -----------

SQL>  select last_name, hire_date from employees where hire_date = '17-8月-2005';
LAST_NAME                 HIRE_DATE
------------------------- -----------
Fay                       2005/8/17

SQL>  select last_name,   hire_date  from  employees  where  hire_date like '17-8月-2005';
LAST_NAME                 HIRE_DATE
------------------------- -----------

SQL>  select last_name, hire_date from employees where hire_date like '%7-8月-2005';
LAST_NAME                 HIRE_DATE
------------------------- -----------

为啥导入老师代码项目完成后显示没有?

1导入项目有什么需要注意的吗?

2.之前导过一次后删除了没选打钩的地方,有什么影响?

3.删除时有个打钩的选项是会删除源码吗?

老师，为啥我的也测试不通过，百度了一下，也没找到相关的解决办法

问题：老师我用c3p0数据库连接池用配置文件实现连接时报错了，你看是我这个xml文件建的有问题吗，还是c3p0-0.9.1.2.jar这个版本还需要依赖别的jar包，下面是报的错，最下面是配置文件图片

六月 19, 2020 10:37:26 上午 com.mchange.v2.log.MLog <clinit>

信息: MLog clients using java 1.4+ standard logging.

六月 19, 2020 10:37:27 上午 com.mchange.v2.c3p0.C3P0Registry banner

信息: Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]

六月 19, 2020 10:37:27 上午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager

信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 5, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> hellc3p0, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge9eiaa1k63i3np8f2kz|e73f9ac, idleConnectionTestPeriod -> 0, initialPoolSize -> 10, jdbcUrl -> jdbc.mysql://localhost:3306/test, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 100, maxStatements -> 0, maxStatementsPerConnection -> 2, minPoolSize -> 10, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]

六月 19, 2020 10:37:47 上午 com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector run

警告: com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@1f407bb -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!

六月 19, 2020 10:37:47 上午 com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector run

警告: com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@1f407bb -- APPARENT DEADLOCK!!! Complete Status: 

Managed Threads: 3

Active Threads: 3

Active Tasks: 

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@4e0ee3ce (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0)

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@6fe6fc6b (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1)

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@7f0acc23 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2)

Pending Tasks: 

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@17088d3d

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@2e211c81

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@767ca88a

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@5fbe09b2

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@c0c061d

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@2a6fc609

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@39440336

Pool thread stack traces:

Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,main]

java.lang.Thread.sleep(Native Method)

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)

com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,main]

java.lang.Thread.sleep(Native Method)

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)

com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,main]

java.lang.Thread.sleep(Native Method)

com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)

com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

六月 19, 2020 10:37:56 上午 com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask run

警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@4e0ee3ce -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 

java.sql.SQLException: No suitable driver

at java.sql.DriverManager.getDriver(DriverManager.java:315)

at com.mchange.v2.c3p0.DriverManagerDataSource.driver(DriverManagerDataSource.java:223)

at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)

at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)

at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)

at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)

at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

六月 19, 2020 10:37:56 上午 com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask run

警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@7f0acc23 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 

java.sql.SQLException: No suitable driver

at java.sql.DriverManager.getDriver(DriverManager.java:315)

at com.mchange.v2.c3p0.DriverManagerDataSource.driver(DriverManagerDataSource.java:223)

at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)

at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)

at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)

at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)

at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

六月 19, 2020 10:37:56 上午 com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask run

警告: com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@6fe6fc6b -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 

java.sql.SQLException: No suitable driver

at java.sql.DriverManager.getDriver(DriverManager.java:315)

at com.mchange.v2.c3p0.DriverManagerDataSource.driver(DriverManagerDataSource.java:223)

at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)

at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)

at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)

at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)

at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

java.sql.SQLException: Connections could not be acquired from the underlying database!

at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:529)

at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)

at com.bjsxt7.connection.C3P0Test.testGetConnection1(C3P0Test.java:31)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)

at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)

at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)

at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)

at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)

at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)

at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)

at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)

at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)

at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)

at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)

at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)

at org.junit.runners.ParentRunner.run(ParentRunner.java:363)

at org.junit.runner.JUnitCore.run(JUnitCore.java:137)

at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)

at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)

at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)

at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.

at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)

at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)

at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)

... 24 more

Process finished with exit code -1

为什么我的dept_id不能定义，只能设置空