> For the complete documentation index, see [llms.txt](https://docs.dwh.dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.dwh.dev/features/data-lineage/default-and-virtual-columns.md).

# Default and Virtual Columns

[**Youtube**](https://youtu.be/eLi8CnXP8LA)

**Default and Virtual Columns** also contain information about data lineage. And as usual, nobody pays attention to it :)

```sql
-- default value
CREATE TABLE t1 (
  id1 int,
  id2 int default (id1 +1)
);

CREATE VIEW v1 AS
  SELECT *
  FROM t1
;
```

If during data transformations, only the id1 column is inserted into the **T1** table, the lineage information will be lost.

At [**Dwh.dev**](https://dwh.dev/), we display it like this:

<figure><img src="/files/kyv6vyqKCGRcnZbyRtPc" alt=""><figcaption></figcaption></figure>

With **Virtual columns**, an even more precarious situation arises. It's impossible to insert data into a virtual column, and they will ALWAYS depend on other columns in the table.

```sql
-- virtual column
CREATE TABLE T2 (
  A INT,
  B INT,
  C INT,
  D INT AS (CASE WHEN A>0 THEN B ELSE C END)
);

CREATE VIEW v2 AS
  SELECT *
  FROM t2
;
```

At [**Dwh.dev**](https://dwh.dev/), we display it like this:&#x20;

<figure><img src="/files/3ve9jKPIOfmvTtcC9fIh" alt=""><figcaption></figcaption></figure>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.dwh.dev/features/data-lineage/default-and-virtual-columns.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.