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System Design Masterclass · Data Governance Compliance
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A data engineer inherits a 50-table database from a team that left the company. No documentation. No data dictionary. Column names like flg_1, amt_adj, and dt_proc. What does flg_1 mean? Is amt_adj in dollars or cents? Is dt_proc a processing date or a creation date?
Data profiling answers these questions by analyzing the actual data. Run profiling on flg_1 and discover it only contains 0 and 1. It is a boolean flag. Profile amt_adj and find values range from -99999 to 99999 with 2 decimal places. It is a dollar amount with adjustments. Profile dt_proc and find dates spanning 2018-2026, with 95% falling on weekdays. It is a processing date, not creation.
Data profiling is the systematic examination of data to understand its structure, content, quality, and relationships. It is the first step before any data migration, integration, or quality improvement. You need to understand what you have before you can fix it.
Uber's data platform team profiles every new table before it enters the . They found that 15% of columns in their legacy systems had misleading names, and 8% had data types that did not match the actual content. Profiling caught these issues before they corrupted downstream analytics.
| Analysis Type | What It Shows | Example Findings |
|---|---|---|
| Column statistics | Min, max, mean, median, std deviation, null count | "age" ranges 0-999, 12% null, mean = 34 |
| Value distribution | Most frequent values, histogram | "status" is 80% active, 15% inactive, 5% suspended |
| Pattern analysis | Common formats in string columns | "phone" has formats: (xxx) xxx-xxxx (60%), xxx-xxx-xxxx (30%), international (10%) |
| Uniqueness | Distinct values vs. total rows | "email" has 99.7% unique. 0.3% duplicates exist |
| Null analysis | Which columns have missing data, how much | "address_line_2" is 65% null, expected for apartments |
| Cross-column correlation | Relationships between columns | When "country" is "IN", "currency" is always "INR" |
| Referential integrity | Do foreign keys match? | 2.1% of "order.customer_id" values do not exist in "customers" table |
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