I am trying to join a .csv file with a .shp file in QGIS but QGIS is unable to read the data in my .csv file as it indicated that the variables are string of length and precision 0. As a result, I am unable to use the method of create a new column of numeric characters and the option to add a new column or to use the field calculator is disable in my attribute table.
The solution may be to create a .csvt file, in the same folder as your .csv file, where you just write the data type. For instance:
"String", "String", "String", "String", "String", "Integer"