IDEA Error: Unknown system variable ‘tx_isolation’ at

java.sql.SQLException: Unknown system variable ‘tx_isolation’ at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1094) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4208) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4140) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2597) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2758) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2820) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2769) at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1569) at com.mysql.jdbc.ConnectionImpl.getTransactionIsolation(ConnectionImpl.java:3372) at com.mchange.v2.c3p0.impl.NewPooledConnection.(NewPooledConnection.java:107) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:198) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014) at com.mchange.v2.resourcepool.BasicResourcePool.access800 ( B a s i c R e s o u r c e P o o l . j a v a : 32 ) a t c o m . m c h a n g e . v 2. r e s o u r c e p o o l . B a s i c R e s o u r c e P o o l 800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool800(BasicResourcePool.java:32)atcom.mchange.v2.resourcepool.BasicResourcePoolAcquireTask.run(BasicResourcePool.java:1810) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

Solution:
1. the version of mysql-connector-java is too low and you need to upgarde to version 8.0.*
2. After you had upgraded the version of mysql-connector-java, update the driver:
com.mysql.jdbc.Driver——>com.mysql.cj.jdbc.Driver

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