输入掩码通常包含原义字符。
原义字符是在查询语句中包含的一个字符，数字或者是时间数据。
A literal is a character, a number, or a date that is included in the SELECT statement.
返回带格式字符串的子字符串，也可以选择包含提示字符和原义字符。
Returns a substring of the formatted string, optionally including prompt and literal characters.
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