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A join that keeps every row from the first (left) table and adds matching data from the second table, leaving the second table's columns empty (null) where there is no match.
Example
Raket Parts B.V. has 436 customers. A left join from customers to their January to September 2025 orders keeps all 436, and 22 of them come back with empty order columns: they placed no order in that period. An inner join would hide those 22 customers, which are exactly the ones an account manager needs to see.
Raket Parts B.V. is a fictional company created for Insyt.
Why it matters
It is how you find what is missing, such as customers without orders or products never sold.
Where it is used
SQL queries, data quality checks and BI models. Used by data analysts, BI developers and data engineers.
For your role
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