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KajoData articles about SQL. Practical knowledge about data analysis, tools and careers.
Articles: 6
expert
Zastanawiasz się, jak wygląda codzienność inżyniera danych? W tym wywiadzie z Darkiem Butkiewiczem (NIEINFORMATYK) poznasz kulisy tej pracy, realne technologie i wskazówki dla osób myślących o przebranżowieniu.
SQL
The average customer places a few orders. But how many buy once, and how many return regularly? I build the distribution step by step, including the mistakes that make valid SQL answer the wrong question.
SQL
A pivot can look correct while losing orders. I show how to count categories, distinguish zero from missing data and reconcile the columns with the source.
SQL
A query with three CTEs can look impressive while calculating the wrong sales total. I build one analysis step by step, keeping track of row meaning, missing values and the order of calculations.
SQL
A query can run successfully and answer the wrong question. I work through six orders to show how selection, grouping, missing values and result checks fit together.
Career & business
A query can run successfully and still answer the wrong question. Work through order grain, joins, missing amounts and a reproducible reconciliation.
