The SQL standard imposes a constraint on window functions that they cannot be used in SQL标准对窗口函数施加了一个约束，它们不能在UPDATE or DELETE statements to update rows. UPDATE语句或DELETE语句中用于更新行。Using such functions in a subquery of these statements (to select rows) is permitted.允许在这些语句的子查询中使用这些函数（选择行）。
MySQL does not support these window function features:MySQL不支持以下窗口功能：
DISTINCT syntax for aggregate window functions.DISTINCT语法。
Nested window functions.嵌套窗口函数。
Dynamic frame endpoints that depend on the value of the current row.依赖于当前行的值的动态帧终结点。
The parser recognizes these window constructs which nevertheless are not supported:解析器可以识别这些不受支持的窗口构造：
The GROUPS frame units specifier is parsed, but produces an error. GROUPS框单位说明符被解析，但产生错误。Only 仅支持ROWS and RANGE are supported.ROWS和RANGE。
The 已分析框架规范的EXCLUDE clause for frame specification is parsed, but produces an error.EXCLUDE子句，但会产生错误。
IGNORE NULLS is parsed, but produces an error. IGNORE NULLS会被解析，但会产生错误。Only 仅支持RESPECT NULLS is supported.RESPECT NULLS。
FROM LAST is parsed, but produces an error. FROM LAST被解析，但产生一个错误。Only 只支持FROM FIRST is supported.FROM FIRST。