A Guide to Ad Hoc Distributed Queries Enable – Process, Usage, and Risks

With SQL Server environment, there are so many concepts that remain new for many users. One such concept is the ad hoc distributed queries enable in SQL Server. But what it is and why do we use them? In this complete write-up, we will learn about the Ad Hoc queries and will also try to figure out how to use them and how exactly they benefit the database administrators. 

So, without any delays, let’s proceed with understanding these queries, before we get any more confused by the term.

What is Ad Hoc Query in SQL? A Complete Overview

To learn what ad hoc distributed queries enable is, the users must know what is ad hoc actually and what we are dealing with. By definition, these are one-time queries in SQL Server that DBAs generally uses only once without storing. These queries in SQL Server that are not in the scope of any future use. Moreover, these queries can access data or files from a remote server or files linked without requiring a server configuration. 

Here are a few cases where these queries are used to make it simpler for the users to understand:

• We use these queries when we have to quickly check database performance or inconsistencies in the database. 
• Ad Hoc distributed queries are also used frequently by the analysts for data exploration, or validate data facts. 
• These queries are also very beneficial for database maintenance checks and validations. 

If we sum up all these cases and situations, it simply means that we use these queries for a short-term requirement without storing them permanently or without the need to pre-define them. 

They support quick data investigation, error/issue troubleshooting in the database, or work efficiently as situational queries without much administrative effort. Now, this is just the definition for Ad Hoc. Moving on, let’s understand the types of ad hoc queries in SQL Server databases. 

Types of Ad Hoc Distributed Queries Explained

Proceeding with the ad hoc distributed queries enable, we will now learn more about its types and understand what these types are and how they are different.

The ad hoc queries in SQL Server are basically of three types. Let’s take a look at each of them to know them better:

1. The first one is the Standard Ad-Hoc Query. These queries are mainly executed directly in SSMS-like tools and carry out the desired tasks. 
2. Next, the category is the Dynamic Ad-Hoc Query in SQL Server. This query is generated at the runtime. What makes it different is that it is generated by the applications that can create queries and commands depending on certain conditions, filters or user requirements. 
3. The last category is Ad Hoc distributed queries. These are capable of accessing the external data sources with the help of features like OPENROWSET and OPENDATASOURCE. These options often allow users to retrieve data from remote servers efficiently. 

The last type of query is the one we are discussing here. These queries help database administrators to fetch the data from remote servers. So now we are aware of what these files are and what are the categories they are divided into. Let’s now take a look at how these queries are processed by SQL Server. 

Ad Hoc Distributed Queries Enable – How the Queries are Processed in SQL Server?

To learn the working of Ad Hoc SQL queries in SQL Server, we will now understand the processing and execution of these queries. Below is the step-by-step process on these queries processing for the desired operations. 

• Submitting the Ad Hoc Queries in SQL Server: The first step is the submission of the ad hoc distributed queries to SQL Server.  
• Syntax Validation: The next part is the validation of query syntax. The SQL Server then parses and verifies the syntax of the ad hoc queries and further checks the objects such as columns, tables, and associated permissions. 
• Compilation of the Query in SQL: Then, the next step is the compilation of the queries. For this, the query optimizer creates an execution plan based on the indexes, statistics available, and the current server conditions of SQL.  
• Execution Plan Caching: For the execution, a compilation plan is then stored in the plan cache. In case of ad hoc distributed queries, SQL Server marks these plans for single-use, as users generally do not use queries again. 
• Execution of Query: After the execution plan, SQL Server finally executes the plan and further retrieves the data as required or needed by the query. 
• Memory and Resource Consumption: As for each ad hoc SQL Server query, some memory space is allotted; if there are several different ad hoc queries, they might end up consuming more of the CPU and memory. This can happen due to recurring compilations of the queries and unused cached plans in the database. 
• Reuse or Elimination of Query: In case a database administrator runs the same ad hoc query again, the SQL Server engine will use the cached plan again. If not, the SQL Server will remove the plan cache. 

Ad Hoc Distributed Queries Security Risk – The Silent Threats

Here are some of the risks that a user or database administrator can encounter while working with the ad-hoc queries in the database. 

• Unauthorized Access to the Remote Data Sources
• Trespassing the Connected Server Security Controls
• Attack Surface Growth in SQL Server
• Threat for Data Exfiltration
• Risks of Violating Compliance Regulations 
• Higher Risks of SQL Injection Attacks

These are some of the common risks that come along with ad hoc distributed queries enable in SQL Server. Most occur because with the ad hoc queries, the SQL Server gets direct access to the external data sources while bypassing the security controls. Furthermore, with this, the attack surface also increases for the attackers. With the execution of these queries for remote servers, they can also result in higher chances of different types of SQL Injection attacks, risking the data confidentiality of the users. So, what can we do if that happens? The first answer is not panic, and then go for a solution that can help recover the data after a similar attack. Let’s now see how that works.

Recover SQL Injection Affected Data with a Professional Solution

As we read, the ad hoc distributed queries allow users to access the data that has been stored on a remote server or in another application. But doing that also leads to some threats, including unauthorized access and SQL injection attacks. Once the data has been affected by such attacks, there aren’t many ways that can help the users get their data back. In such cases, it is important to go for a professional solution like SysTools SQL Recovery Tool. This utility is designed with many advanced features, including the recovery from SQL Injection attacks. 

Let’s take a look at how this tool works step-by-step:

1. Install and run the tool. Click on Open to browse the affected file.
2. Next, choose a scan mode from Quick Scan and Advance Scan to check for any corruption in the file.
3. After the scan, preview the recovered files. Then click on the Export Tab to proceed.
4. In the Export window, choose the destination and add authentication details.
5. Next, choose the data you want to export and then click on the Recover Button.

Following these steps will help with recovering the data after SQL injection attacks due to ad hoc distributed queries enable. But, it is still important to run the queries with complete precautions to avoid risks of data breaches or permanent data loss. 

Best & Safe Practices to Prevent Data Risks due to Ad Hoc SQL Queries

• The first measure is to disable the ad hoc distributed queries unless there is some crucial task that requires such query execution.
• Do not grant complete access to all users. Instead, grant the least permissions to users and further limit the ad hoc users’ access to the sensitive or crucial data and tables. 
• The parameterized queries reduce the risk of SQL Injection attacks; hence, it is beneficial to use parameterized queries in SQL Server to keep the data safe. 
• With the help of regular monitoring and auditing, it becomes easier for the database administrators to detect any unusual exports and access patterns in the databases. 
• Encrypt the data that is too crucial or sensitive for non-admin users. This will help database administrators and users to keep their data secure even with the ad hoc queries enabled. 

Wrapping Up

Coming to an end, let’s recall what we learned today. With the help of this technical write-up, we discussed ad hoc distributed queries enable thoroughly. Along with the definition, we also learned its types and how it is processed in SQL Server. Even though the query is helpful for the users, there are still risks to using it. Hence, we suggested a professional solution to help users if they end up compromising data to these risks.