它不会对数值字段生效，除非这些字段具有一致的长度。
It does not work on numeric fields unless the fields are all the same length.
数值字段被赋以0值，而字符串字段则赋以空字符串值。
Numeric fields are given the value 0, and string fields have the empty string value.
一个字符被转换为数值形式来存储进数值字段或变量中。
A character value is being converted to numeric form for storage in a numeric column or variable.
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