Identifier consistency across systems
Identifier consistency across systems covers two areas: the identifier level (product or variant) and the identifier type (SKU, id, EAN, MPN and so on).
1. Identifier level: product or variant
Different identification levels across systems make joining data hard, because product sales cannot be assigned to variant sales.
Example: Google Analytics 4 uses item_group_id. We know the Classic T-shirt sold 3 times and generated PLN 450 in revenue, but not which variants sold. Google Ads uses id, so costs are assigned to individual variants:
| Variant | item_group_id | id | Spent |
|---|---|---|---|
| Classic T-shirt, white, size S | 1 | a | 15 zł |
| Classic T-shirt, white, size M | 1 | b | 2 zł |
| Classic T-shirt, black, size S | 1 | c | 5 zł |
The most precise information sits at the last identification level, the variant. To join GA4 and Google Ads data, both must be reduced to a common identifier, item_group_id, because there's no way to split PLN 450 of revenue across variants. Data quality suffers: we only know the Classic T-shirt (item_group_id: 1) earned PLN 450 and spent PLN 22, not which variant is the most popular.
| Variant | item_group_id | id | Spent | Revenue |
|---|---|---|---|---|
| Classic T-shirt, white, size S | 1 | a | 15 zł | 300 zł |
| Classic T-shirt, white, size M | 1 | b | 2 zł | 0 zł |
| Classic T-shirt, black, size S | 1 | c | 5 zł | 150 zł |
When every system works at the variant level, we know exactly which product is the most popular.
2. Identifier type: SKU, id, EAN, MPN and so on
The second key dimension is the identifier type. Products often carry several identifiers:
- product card number (often assigned automatically by the shop panel)
- warehouse number
- accounting number
- SKU
- MPN
- GTIN
Bad: each system uses a different identifier
- Google Analytics 4: product card number
- Google Ads: SKU
- Meta Ads: warehouse number
Good: one identifier everywhere
- Google Analytics 4: SKU
- Google Ads: SKU
- Meta Ads: SKU
With different identifiers, data from these systems can't be joined simply; extra mappings between systems are needed.
Good practice: give each product one identifier and use it in every system: the shop panel, accounting and warehouse systems, marketplaces and ad platforms.
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