Join a table to existing vector data using a common field or column to match on using the Join tool.
To join a table, press the Join Attributes button in the Attribute Editor, or from the layer menu choose Join Attribute Table/File to Layer. This tool also available by right-clicking on the layer in the Control Center and going to the Layer submenu, then select JOIN- Join Attribute Table/File to Layer
The data in this example table join comes from the World Bank.
https://data.worldbank.org/data-catalog/ed-stats
File Name — Choose the table to join. Supported formats include csv, txt, dbf and other simple ascii text files.
Join File Delimiter — Specify the delimiter used in the file to separate values. If the join file is a DBF, this field is not applicable, and will be disabled.
Join File Attribute — Select the name of the attribute that matches an attribute in the existing layer. This is sometimes referred to as the Foreign Key or Common Attribute. The attribute names come from the first row of the table.
Attributes to Copy — Put a check next to each attribute to be copied, or remove the check to prevent an attribute from being copied. By default, all attribute names are selected. At least one attribute must be selected to join.
Click the Select All button to restore the check next to all of the attributes. Click the Clear All button to remove the check from all attributes.
When duplicate records are found there is a prompt providing options for handling the duplicate values:
Use case-sensitive comparisons — specifies whether or not text comparisons are case sensitive or not. Check this option to enable. By default comparisons are not case sensitive.
Ignore whitespace when looking for matches— specifies whether or not whitespace (i.e. spaces and tabs) should be ignored when looking for matches to join on. Check this option to ignore whitespace. By default whitespace is considered.
The preview at the bottom of the dialog shows an example of the external table that will be added to the vector features.