Your expression is building a query string for use in a Web.Contents call. Different parts of your code each separately compute parameters that should be included in the final query string. These are provided as “query fragment” records, which all need to be combined into a single, consolidated record that’s then passed to Web.Contents:
ProductCodeFragment = GetProductCodeQueryFragment(), // might return [productId = 123]
LimitFragment = GetLimitQueryFragment(), // might return [limit = 100]
FinalQueryParams = (single, consolidated record containing query parameters from all fragment records, such as ProductCodeFragment and LimitFragment),
Result = Web.Contents("some-url", [Query = FinalQueryParams]
Using Power Query’s built-in functionality, combining the fragment records into a consolidated record is easy, so long as the fragment records each have different fields. If they do, a record merge can be performed using the combination operator (&) or the records can be combined using Record.Combine, both of which produce the same output.
[productId = 123] & [limit = 100] // outputs [productId = 123, limit = 100]]
Record.Combine({[productId = 123], [limit = 100]}) // outputs [productId = 123, limit = 100]
The challenge comes if multiple records contain the same field—say, one fragment record contains [productId = 123] while another contains [productId = 456]. Record.Combine and & are exclusive in how they compute the field values they output. When the same field name is present in multiple input records (e.g. both input records contain field productId), the value for that field that’s output will be the value from the last/right-most input record (in this case, productId = 456). The other input record value(s) for that field will be ignored (so in this case, productId = 123 is ignored).
// notice that productId 123 is *not* included in the outputs
[productId = 123] & [productId = 456] // outputs [productId = 456]
Record.Combine({[productId = 123], [productId = 456]}) // outputs [productId = 456]
