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Video of Self Join in SQL in Database ERD Principles course by Database Star channel, video No. 5 free certified online
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A self join in SQL is where you write a query on one table that joins to the same table a second time. It's used when you have a record in the table that refers to another record in the same table.
A common example is employees and managers, or product categories. Anything with a "hierarchical data" setup may use an SQL self join.
This video shows you what an SQL self join is, how to write one, and how to overcome issues with column names and missing data.
You can find out more about joins overall in this guide here: https://www.databasestar.com/sql-joins/
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Timestamps:
00:00 Introduction
00:12 Self Join definition
01:38 Employee solution
06:03 Final query
06:45 Categories example
07:30 Left Join