# Self-Increasing Id (Continue...)

+ Restrictions on use:
  + Must be defined on the column of the primary key or unique index
  + Can only be defined on columns of type integer, FLOAT, or DOUBLE
  + Specifying on the same column as the default value of the column DEFAULT is not supported
  + Adding the AUTO_INCREMENT attribute with ALTER TABLE is not supported
  + You need to control whether the AUTO_INCREMENT attribute is allowed to be removed by ALTER TABLE via the session variable @ @tidb_allow_remove_auto_inc; by default, this attribute is not allowed to be removed

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