Inspect an Access Lookup Field’s Stored Key Before Writing Its Criteria
A datasheet can show a friendly location name while storing a numeric location key. If a query treats the visible name as the field's stored text, the criteria can be aimed at the wrong representation.
Work in a copy of the desktop Access query. Choose one known record and note its visible location and the reference-table entry it should identify. Use the key and label together while investigating; two locations can have similar names without being the same record.
Reveal the value being queried
Access normally shows a lookup field's display value in query Datasheet View. Microsoft describes exposing its bound value in Design View: select the lookup field in the grid, open Property Sheet, choose the Lookup tab and set Display Control to Text Box. Inspect the result in the query copy rather than changing the stored keys to match what was previously displayed.
For a fictional example, a record may show Workshop while its bound key is 12. Confirm that key 12 identifies the intended Workshop entry in the related table. The number is a reference, not an alternative spelling of the label.
Put label criteria on the label field
To filter using the display name, Microsoft's procedure adds the related lookup source to the query, joins it appropriately and applies criteria to that source's label field. Keep the bound key visible during the check, even if the finished report will show only a readable label.
Use one expected matching record and one that should be excluded. Inspect their keys and related labels in the query result. If two reference rows share the same display name, determine whether name-based criteria are intentionally meant to include both.
Do not rewrite stored numeric keys as text names to make a single filter convenient. That would change the data model rather than clarify the query. Resolve a broken relationship or incorrect reference entry at its actual source with the database owner.
Save the reviewed query under a clear name and document whether its criteria operate on keys or labels. This makes later troubleshooting possible when a friendly name is renamed but its underlying identity remains the same.
Sources: Microsoft: querying Access lookup fields.