For each non-NULL variable-length field, the record header contains the length of the column in one or two bytes.

对于每个非空的变长字段，记录头使用一或两个字节包含了列的长度。

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Next check if the cursor contains records and if so loop through them. The record ID field is stored in the id variable. This will be used as a where parameter later.

下一步检查游标是否包含记录，如果包含记录，侧记录ID字段的值存储在ID变量中。

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