Transact-SQL Error Messages

This section provides detailed information about Transact-SQL (T-SQL) error messages, their causes, and potential solutions. Understanding these errors is crucial for debugging and developing robust SQL Server applications.

Common T-SQL Error Categories

  • Msg 102, Level 15, State 1

    Incorrect syntax near 'keyword'. This error typically indicates a misspelled keyword, missing punctuation, or incorrect placement of clauses in your T-SQL statement.

    Learn More about Syntax Errors
  • Msg 208, Level 16, State 1

    Invalid object name 'ObjectName'. This error occurs when the database engine cannot find the specified table, view, stored procedure, or other object.

    Learn More about Invalid Object Names
  • Msg 122, Level 15, State 1

    A number is expected. This error usually means a numeric value was expected but something else (like a string or a variable without a value) was provided.

    Learn More about Data Type Mismatches
  • Msg 515, Level 16, State 2

    Cannot insert the value NULL into column 'ColumnName', table 'TableName'. Column does not allow nulls. This error is raised when you attempt to insert or update a row with a NULL value in a column that is defined as NOT NULL.

    Learn More about NULL Violations
  • Msg 1205, Level 13, State 2

    Transaction (Process ID: 123) was deadlocked on [Resource] by another process and has been chosen as the deadlock victim. Rerun the transaction. This indicates a deadlock situation where two or more processes are waiting for each other to release locks.

    Learn More about Deadlocks

Syntax Errors

Syntax errors are among the most common. They occur when T-SQL statements do not conform to the rules of the T-SQL language.

Example:


SELECT Column1, Column2
FROM MyTable
WHERE Column3 = 'Value' -- Missing semicolon here can sometimes cause issues depending on context
GROUP BY Column1 -- Incorrect clause order
ORDER BY Column2 DESC

Common causes:

  • Typos in keywords (e.g., SELCT instead of SELECT)
  • Missing or misplaced commas, parentheses, or other punctuation.
  • Incorrect order of clauses (e.g., ORDER BY before GROUP BY).
  • Using reserved keywords as identifiers without proper quoting.

Invalid Object Names

When SQL Server cannot find a referenced object (table, view, stored procedure, etc.), it returns Msg 208.

Troubleshooting:

  • Verify the object name for spelling mistakes.
  • Check if the object exists in the current database context.
  • Ensure you have the necessary permissions to access the object.
  • If the object is in a different database, use the three-part name format: DatabaseName.SchemaName.ObjectName.

Data Type Mismatches

These errors occur when an operation expects a certain data type but receives another, or when attempting to convert data implicitly or explicitly fails.

Example: Trying to add a string to an integer column.


-- Incorrect: Cannot add string to an integer column
UPDATE MyTable
SET NumericColumn = NumericColumn + 'abc';

-- Correct: Explicitly cast or ensure data types match
UPDATE MyTable
SET NumericColumn = NumericColumn + CAST('123' AS INT);

NULL Violations

Occurs when attempting to insert a NULL value into a column that does not permit nulls (NOT NULL constraint).

Solutions:

  • Provide a non-NULL value for the column.
  • If a default value is not specified, ensure your application logic handles cases where a value might be missing and provides a suitable alternative.
  • Review the table schema definition.

Deadlocks

Deadlocks happen when two or more processes require locks on resources that the other process currently holds, creating a circular dependency.

Mitigation Strategies:

  • Keep transactions short and concise.
  • Access objects in a consistent order across all transactions.
  • Use appropriate isolation levels.
  • Minimize the number of operations within a transaction.
  • Implement retry logic in your application for deadlocked transactions.

Further Resources