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retl-model-limitations #6191

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retl-model-limitations #6191

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7 changes: 7 additions & 0 deletions src/connections/reverse-etl/index.md
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Expand Up @@ -307,6 +307,13 @@ Column name length | The maximum length of a record column. | 128 characters
Record JSON size | The maximum size for a record when converted to JSON (some of this limit is used by Segment). | 512 KiB
Column JSON size | The maximum size of any single column value. | 128 KiB

### Data Model limits

We execute model queries inside a [common table expression](https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#cte_rules), there are some constraints to consider when working with CTEs.

1. Session variables can not be used as CTEs do not support certain operations, including `SET`.
2. We can only bind the results from one single subquery. If there are multiple semi-colons `;` in the customer query, they'll be treated as several subqueries, which will result in a syntax error.

## FAQs

#### Why do my sync results show *No records extracted* when I select *Updated records* after I enable the mapping?
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