PySpark Null Handling

11 interview problems on coalesce, fillna and three-valued logic, from easy to hard.

• Replace Missing Values · Easy · Null Handling
• Unpivot Wide Columns to Rows · Medium · Pivot, Unpivot & Rollup
• Joining on Nullable Keys · Medium · Joins
• Data Quality: Null Count per Column · Medium · Null Handling
• Pivot with Several Aggregations · Hard · Pivot, Unpivot & Rollup
• Sessionize a Clickstream · Hard · Window Functions
• Build an SCD Type 2 History · Hard · Window Functions
• Price Valid at Order Time (Range Join) · Hard · Joins
• Reconcile Two Sources (Full Outer Join) · Hard · Joins
• Fill Missing Dates (Calendar Spine) · Hard · Joins
• Monthly Retention by Cohort · Hard · Joins

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Topics: Window Functions · Joins · Aggregations · Pivot, Unpivot & Rollup · Arrays · Null Handling · Conditional Logic · Dates · Filtering & Selection · Strings

Difficulty: Easy · Medium · Hard · PySpark interview roadmap · All problems