How do I complete an existing attribute table with .CSV or .XLSX

Question

I have an existing vector layer (points) I was working on some time ago. The layer represents boreholes in the area of my interest (over 250 points).

Some time ago we got access to a number of geological documentations and my colleague updated some of the information regarding the boreholes in the Excel file. He used the same headers that I used in QGIS.

Is it possible in QGIS after adding a CSV or XLSX file for the join to fill in the missing gaps in an existing column rather than adding a completely new column?

For example, in the screenshot, you see a column named "do_str_wwy" - it represents the depth to the aquifer.

In the XLSX file, I have an identical column with completed values for the selected boreholes. What I want to accomplish is to fill in the NULL values in the existing column, because right now QGIS creates a whole new column every time and I don't know how it will handle this.

Answer 1

Using the examples you've shown, if you are using the Odwiert_na column as the key column to perform the join, you can use field calculator in your vector layer to overwrite the do_str_wwy column in one stroke with the following expression (replace new_layer_name accordingly). Note the use of single and double quotes

 attribute(get_feature('new_layer_name','Odwiert_na',"Odwiert_na"),'do_str_wwy')

This is essentially a lookup/join expression. This overwrites the entire column.

The structure works like this:

attribute(get_feature('other_layer_name','other_layer_matching_key_column',"current_layer_key_column"),'other_layer_desired_attribute')

get_feature() goes through your current layer's key column and grabs a matching feature (row) from the other layer based on matching values in the other layer's specified column.

attribute() then extracts the specific attribute from that matching feature.

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Or if you want to keep the existing values in do_str_wwy in your vector layer, and only fill in values if the field is NULL,

coalesce("do_str_wwy", attribute(get_feature('new_layer_name','Odwiert_na',"Odwiert_na"),'do_str_wwy'))

coalesce() returns the first non-null value so if do_str_wwy has a value, it uses that, otherwise it applies the lookup expression.