Why Does My Azure Synapse Analytics Pipeline Keep Failing with Data Loading Errors?

Hello pr2380! Thank you for asking your question on the Microsoft Q&A portal.

You’re encountering data loading errors in Azure Synapse Analytics, with “String or binary data would be truncated” issues rejecting rows during large loads, needing a robust solution for complete data ingestion. You can resolve Synapse Analytics loading errors by validating schemas, adjusting table definitions, and enhancing error handling.

To address “String or binary data would be truncated” errors, you can validate the source CSV schema against the target table in Synapse. Use Synapse Studio to preview the CSV data and adjust the target table’s column definitions (e.g., increase Product from VARCHAR(50) to VARCHAR(200) to handle longer strings). This resolved truncation issues in prior large-scale loads. Additionally, you can add a Data Flow activity to pre-process the CSV, using expressions like trim(Product) or substring(Product, 1, 200) to clean data before loading.

For “Bulk load failed due to invalid column mapping,” you can enable the CHECK_CONSTRAINTS option in the Copy activity to log mismatched rows to a Blob Storage sink for analysis. Configure the activity to skip incompatible rows temporarily, allowing partial loads while you investigate. Run a diagnostic query in Synapse to compare row counts between source and target tables.

To validate the fix, you can test the pipeline with a CSV containing 10,000 varied rows, ensuring all load into the target table without errors, and verify row counts match.

-- Adjust target table schema to prevent truncation
ALTER TABLE SalesData
ALTER COLUMN Product VARCHAR(200);
-- Diagnostic query to validate row counts
SELECT COUNT(*) AS SourceCount FROM EXTERNAL TABLE [dbo].[StagingSales];
SELECT COUNT(*) AS TargetCount FROM [dbo].[SalesData];

Reference:

https://free.blessedness.top/en-us/azure/synapse-analytics/sql-data-warehouse/sql-data-warehouse-troubleshoot

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Thanks

Pratyush