删除具有外键约束的 Mysql 表列

Question

如何删除 mysql 中所有相关外键和其他约束的列？

Answer 1

使用SET FOREIGN_KEY_CHECKS = 0; 然后更改包含约束定义的表。 完成后，将FOREIGN_KEY_CHECKS转回 1。

Answer 2

MySQL 上的 AFAIK您必须在删除列之前手动删除约束。

仅当您使用该子句创建约束时，ON DELETE CASCADE 子句才会影响该表，并且只需要删除与该约束的该表连接的外部行。

Answer 3

如果您使用的是 java：

public void deleteColumn(Connection connection, String tableName, String columnName) throws SQLException {
    // Drop all constraints that contain the specified column
    {
        final ResultSet resultSet = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY).executeQuery("select CONSTRAINT_NAME from INFORMATION_SCHEMA.KEY_COLUMN_USAGE where CONSTRAINT_SCHEMA = SCHEMA() and TABLE_NAME = '" + tableName + "' and COLUMN_NAME = '" + columnName + "'");
        while (resultSet.next()) {
            final String constraintName = resultSet.getString("CONSTRAINT_NAME");
            connection.createStatement().executeUpdate("ALTER TABLE `" + tableName + "` DROP FOREIGN KEY`" + constraintName + "`"); // Drop the foreign key constraint          
        }
        resultSet.close();
    }

    // Drop all indexes that contain the specified column:
    {
        final ResultSet resultSet = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY).executeQuery("SHOW INDEX FROM `" + tableName + "` where column_name = '" + columnName+ "'");
        while (resultSet.next()) {
            final String keyName = resultSet.getString("Key_name");
            connection.createStatement().executeUpdate("ALTER TABLE `" + tableName + "` DROP INDEX `" + keyName + "`"); // Drop the index               
        }
        resultSet.close();
    }

    // Drop the column:
    connection.createStatement().executeUpdate("ALTER TABLE `" + tableName + "` DROP COLUMN `" + columnName + "`"); // Drop the column
}

Answer 4

使用 ON DELETE CASCADE

http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html