What Are Statistics in Fabric Data Warehouse & How to Manage Statistics | Microsoft Fabric Tutorial

What Are Statistics in Fabric Data Warehouse & How to Manage Statistics

In this Microsoft Fabric tutorial, we explain what statistics are in a Fabric Data Warehouse, why they are critical for performance, and how to manage them manually or automatically using T-SQL.

📊 What Are Statistics?

Statistics describe the distribution of values in a column
Used by the query optimizer to estimate row counts and selectivity
Critical to choosing an efficient query execution plan

🔧 Manual Statistics Management

Create, update, and inspect statistics on frequently filtered or joined columns:

-- Create statistics manually
CREATE STATISTICS DimCustomer_CustomerKey_FullScan
ON dbo.DimCustomer (CustomerKey) WITH FULLSCAN;

-- Update statistics after data changes
UPDATE STATISTICS dbo.DimCustomer (DimCustomer_CustomerKey_FullScan) WITH FULLSCAN;

-- View histogram of statistics
DBCC SHOW_STATISTICS ('dbo.DimCustomer', 'DimCustomer_CustomerKey_FullScan') WITH HISTOGRAM;

⚙️ Automatic Statistics

Automatically created when queries involve JOIN, GROUP BY, WHERE, or ORDER BY
Generated under names like _WA_Sys_...
Automatically refreshed when underlying data changes significantly

-- Query that triggers auto-stat creation
SELECT CustomerKey FROM dbo.DimCustomer GROUP BY CustomerKey;

-- View system-generated statistics
SELECT
    object_name(s.object_id) AS object_name,
    c.name AS column_name,
    s.name AS stats_name,
    STATS_DATE(s.object_id, s.stats_id) AS stats_update_date,
    s.auto_created
FROM sys.stats s
JOIN sys.stats_columns sc ON s.stats_id = sc.stats_id AND s.object_id = sc.object_id
JOIN sys.columns c ON sc.object_id = c.object_id AND sc.column_id = c.column_id
WHERE object_name(s.object_id) = 'DimCustomer';

💡 Best Practices

Create stats manually for columns heavily used in WHERE and JOIN clauses
Use WITH FULLSCAN for higher accuracy
Inspect STATS_DATE to verify freshness
Allow auto stats to handle low-frequency changes

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