今天寫的一個項目需要更換數據庫地址，項目框架是SSH，數據庫連接用的是c3p0，結果換了數據庫連接地址、用戶名、密碼之後始終連接不上數據庫（確認連接信息和數據庫本身沒有問題），然後日誌信息爲：
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 5, acquireRetryAttempts -> 0, acquireRetryDelay -> 1000000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> h4qly89seldn7schml8v|603698f, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> h4qly89seldn7schml8v|603698f, idleConnectionTestPeriod -> 1800, initialPoolSize -> 5, jdbcUrl -> jdbc:mysql://120.27.76.193:3360/wpwemall, lastAcquisitionFailureDefaultUser -> null, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 1800, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 10, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> select id from user where id=1, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> true, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
後來在網上找了好多都是出現這個問題，但是都沒有解決辦法
最終發現c3p0的配置中有一個定義連接的測試語句
c3p0.preferredTestQuery=select id from user where id=1
發現該測試語句指定的是user表，而我換的新的數據庫中沒有這個測試的數據表，最終導致了上面的現象
其實只要將這句話該爲默認的即可
mysql: select 1
oracle: select 1 from dual
