DROP USER [ if exists ] user_name; 其中，user_name： 要删除的用户名。if exists：要删除的用户是否存在。 不指定if exists选项时，如果要删除的用户不存在，会提示错误信息。指定if exists选项时，如果要删除的用户不存在

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Join)是一种特殊的连接类型，在SQL中没有指定的关键字，通过在WHERE后面使用IN或EXISTS子查询实现。当IN/EXISTS右侧的多行满足子查询的条件时，主查询也只返回一行与IN/EXISTS子查询匹配的行，而不是复制左侧的行。 示例：查看参加培训的员工的教育信息。即使tra

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WITH GRANT OPTION ' print @SQL exec (@SQL) SET @SQL=' use [msdb] if exists(select top 1 1 from sys.sysusers where name = '''+ @Login_Name +''')

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MySQL) 反连接 反连接(Anti Join)是一种特殊的连接类型，在SQL中没有指定的关键字，通过在WHERE后面使用NOT IN或NOT EXISTS子查询实现。返回所有不满足条件的行。这个关系的概念跟半连接相反。 示例：查询没有参加培训的员工的教育信息。 文中课程 更多精彩课堂、微认证、沙箱实验，尽在华为云学院

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expression [ NOT ] IN ( select | expression [ , ... n ] ) | [ NOT ] EXISTS ( select ) } 查询条件由表达式和操作符共同定义。常用的条件定义方式如下： 比较操作符“>，<，>=，<=， !=， <>

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to a set of values. Valid operators are In, NotIn, Exists and DoesNotExist. values Array of strings values is an array of string

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unique on the server. If this field is specified and the generated name exists, the server will NOT return a 409 - instead, it will either return

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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unique on the server. If this field is specified and the generated name exists, the server will NOT return a 409 - instead, it will either return

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unique on the server. If this field is specified and the generated name exists, the server will NOT return a 409 - instead, it will either return

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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key's relationship to the value. Valid operators are Exists and Equal. Defaults to Equal. Exists is equivalent to wildcard for value, so that a pod

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unique on the server. If this field is specified and the generated name exists, the server will NOT return a 409 - instead, it will either return

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