mysql数据库去重

mysql数据库去重：

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1) 如果要保留id最小的那一项:

DELETE n1 FROM tableName n1, tableName n2 WHERE n1.columnName = n2.columnName AND n1.id > n2.id;

2) 如果要保留id最大的那一项:

DELETE n1 FROM tableName n1, tableName n2 WHERE n1.columnName = n2.columnName AND n1.id < n2.id;