java - 填充数据库中的外键问题

Question

Deleting previous tuples from flights
 Error: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationExcepti
on: Duplicate entry 'AAH196' for key 'PRIMARY'
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Dupl
icate entry 'AAH196' for key 'PRIMARY'

        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou
rce)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
        at com.mysql.jdbc.Util.getInstance(Util.java:384)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)

        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498)
        at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
        at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
        at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2562)
        at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1664)
        at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1583)
        at Populate.Populate_flights(Populate.java:94)
        at Populate.<init>(Populate.java:36)
        at Populate.main(Populate.java:28)

Deleting previous tuples from reservationsInserting Data into table building Err
or 2: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException
: Cannot add or update a child row: a foreign key constraint fails (`cs585hw3`.`
reservations`, CONSTRAINT `reservations_ibfk_1` FOREIGN KEY (`flight_no`) REFERE
NCES `flights` (`flight_no`))
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cann
ot add or update a child row: a foreign key constraint fails (`cs585hw3`.`reserv
ations`, CONSTRAINT `reservations_ibfk_1` FOREIGN KEY (`flight_no`) REFERENCES `
flights` (`flight_no`))

        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou
rce)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
        at com.mysql.jdbc.Util.getInstance(Util.java:384)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)

        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498)
        at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
        at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
        at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2562)
        at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1664)
        at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1583)
        at Populate.Populate_reservations(Populate.java:126)
        at Populate.<init>(Populate.java:37)
        at Populate.main(Populate.java:28)

我有两张 table 。 flights.data 和 reservations.data。我正在尝试通过 jdbc 填充表。填充它时，出现上述错误。

reservations 到 flights 有一个外键引用。我必须先从辅助表中删除记录。这意味着，我应该在从航类中删除之前从预订中删除记录。那是对的吗？我检查了我的表，预订表有一个外键。所以我必须先从这个表中删除数据。

但是我该如何执行这个任务呢？

在预约功能中，我是这样做的，

Statement s = conn.createStatement();

        s.executeUpdate("DELETE FROM reservations");

在表函数中，它是一样的，相反，我使用了从表中删除。请告诉我如何修复它。

Answer 1

您知道要在航类中删除的行的主键吗？假设它是 5。

long flightId = 5;
Statement s = c.prepareStatement("DELETE FROM reservations WHERE flight_id = ?");
s.setLong(1,flightId);
s.executeUpdate();

届时，您可以删除您的航类，因为不会有任何预订指向它。

s.prepareStatement("DELETE FROM flights WHERE id = ?");
s.setLong(1, flightId);
s.executeUpdate();

编辑:如果你想从两个表中删除所有日期:

Statement s = c.prepareStatement("DELETE FROM reservations");
s.executeUpdate();

s = c.prepareStatement("DELETE FROM flights");
s.executeUpdate();