Why Does SQL Server Truncate CSV Data Even with varchar(MAX) Columns?

Truncation Errors in SQL Server CSV Import Despite varchar(MAX)

Encountering truncation errors while importing a CSV file into SQL Server can be frustrating, especially when the columns are explicitly defined as varchar(MAX). To understand why this occurs, let's delve into the issue.

The SQL Server Import and Export Wizard allows you to manipulate the source data types in the Advanced tab. Typically, the wizard sets the source data type to DT_STR, equivalent to VARCHAR(255), for text columns. However, for columns intended to hold very long strings, such as varchar(MAX), you need to manually change the data type to DT_TEXT.

The truncation error occurs when the wizard attempts to convert the source data to the destination data type. If the destination data type is varchar(MAX), but the source data type is still DT_STR (VARCHAR(255)), the data will be truncated if it exceeds the 255-character limit.

Solution:

To resolve this issue, navigate to the Advanced tab in the Data Source selection of the Import and Export Wizard. Select the offending columns that are experiencing truncation and change their data type from DT_STR to DT_TEXT. You can select multiple columns and make the change simultaneously. This change will ensure that the data is handled correctly during the import process, preventing truncation errors due to character overflow.

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