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Practical guides on working with CSV, Parquet, JSON and SQL — written around the tools on this site, with real examples rather than generic advice.
CSV
Parquet
JSON
SQL
- How to Query CSV Files with SQLRun real SQL — GROUP BY, joins, window functions — against a CSV with no database to set up.
- How to Query Parquet Files with SQLQuery Parquet's columns, including nested ones, and see why some queries answer instantly.
- DuckDB vs Traditional SQL Databases for Local Data AnalysisNo server, no import step, columnar by default: what actually changes for local analysis.
Data quality and profiling
- What Is Data Profiling?What profiling actually computes, and how it differs from a data-quality check.
- What Is Data Quality?A concrete definition: the specific, checkable problems it covers and why language matters.
- How to Find Duplicate Rows in a CSV FileWhy sorting doesn't find duplicates, and where duplicate detection stops working at scale.
- How to Find Missing Values in a CSV FileNULL, an empty string and a whitespace-only value are three different things. Here's why it matters.