删除Mysql表列与外键约束

Question

如何删除所有相关的外键和其他约束列在MySQL？

Answer 1

据我所知在MySQL 你必须删除列前手动删除的约束。

只有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关联的外部行。

Answer 2

使用ON DELETE CASCADE

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

Answer 3

使用SET FOREIGN_KEY_CHECKS = 0;然后更改包含约束定义的表。大功告成后，关闭FOREIGN_KEY_CHECKS回1

Answer 4

，如果你使用的是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 
}