A composite key, in the context of relational databases, is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined; when taken individually the columns do not guarantee uniqueness.

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Join Tables related by a composite primary key in qgis

I have two tables, one has the geometry and other has attributes. The table with geometry has unique number primary key, and 4 columns admin1,admin2,admin3,featureid. Table two is a csv file has the ...