What is Data Truncation in SQL?

Learn what is data truncation in SQL and how to prevent it from happening with this expert's guide. Find out how to detect and fix silent truncation errors.

What is Data Truncation in SQL?

In SQL, the TRUNCATE TABLE statement is a data definition language (DDL) operation that marks extensions of a table for deallocation (emptying it for reuse). This command quickly deletes all records in a table by deallocating the data pages used by the table. However, SQL Server won't allow silent truncation of data just because the column is too small to accept it. There are other ways in which SQL Server can truncate data that is about to be inserted into a table without generating any kind of error or warning.

The TRUNCATE TABLE command removes data from a table, but not the table itself. It is used to delete complete data from an existing table. For example, 'SQLShack ApexSQL Community' inserted into the table after truncation as 'SQLShack A'. This trace flag displays the SQL truncation error message: “String or binary data would be truncated in the table '%.

This issue has been discussed in various forums to improve the error related to silent truncation of data so that it can be quickly fixed. Some of the events you attribute to truncation are actually the result of implicit T-SQL conversions that are implemented for the convenience of developers. So if the data passed is too long for the column, it will be reverted and generate a truncation error instead of silently truncating and inserting. There are certain circumstances in which SQL Server will silently truncate data, without providing any errors or warnings, before inserting it into a table.Now, after truncating the CUSTOMERS table, the output of the SELECT statement will be as shown in the code block below -.

However, unless at least one of the concatenated strings is of a large value type (such as varchar (max) or nvarchar (max)), it will be truncated instead of returning a large value type. This will make many administrators and database developers satisfied with this detailed SQL truncation error message.

Charlotte Wilson
Charlotte Wilson

Friendly travel advocate. Freelance zombie scholar. Extreme web practitioner. Evil coffee buff. Professional beer practitioner.

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