Kết hợp dữ liệu trong SQL

Stack rows from multiple tables into a single unified result, and know when stacking (rather than joining) is the right approach for combining data.

Enrich a base table with additional data without losing any rows, and understand when a left join is the right choice — specifically, when not every row in your primary table has a match in the other table.

Combine only the rows that match across tables, understand how inner joins differ from left joins, and choose between them based on whether unmatched rows matter to your analysis.

Join tables accurately when no single column uniquely identifies matching rows, and recognize the consequences of choosing incorrect join columns.