join a table one to many

[MohamadRahahleh]

I am trying to join a table with many rows to a polygon shape file with less numbers as a one to many relationship for time series; however, I only keep getting the first year for each polygon instead of all the years. I am using ArcMap desktop 10.8

[BarryNorthey]

The table and feature class must be in the same (file) geodatabase to be able tomdo a one-to-many join.

"When using data where a one-to-many or many-to-many relationship exists, you should use a relate or relationship class to establish the relationship between the datasets. However, it is possible to create a join under these circumstances. When you create a join in such a case, there are differences between how tools and other layer-specific settings work depending on the data source. If you are using geodatabase data to create the join, all matching records are returned. If you are using nondatabase data, like shapefiles or dBASE tables, to create the join, only the first matching record is returned".

https://desktop.arcgis.com/en/arcmap/latest/manage-data/tables/about-joining-and-relating-tables.htm