There are only four things you can do with a set of rows in an SQL table: insert them into a table, delete them from a table, update the values in their columns, or query them. The unit of work is a set of whole rows inside a base table.
When you worked with file systems, access was one record at a time, then one field within a record. Since you had repeated groups and other forms of variant records, you could change the structure of each record in the file.
The mental mode in SQL is that you grab a subset, as a unit, all at once in a base table and insert, update, or delete, as a unit, all at once. Imagine that you have enough computer power that you can allocate one processor to every row in a table. When you blow your whistle, ...