Background: I have a bunch of (huge) SHP-files that I would like to merge to one big SHP-file that I can use for geo-processing (clip, etc.). Now I was able to merge a big part of the SHP-files to one big ~ 400 MB SHP-file (Note: This big SHP-file is the result of merging many smaller SHP-files). But this is still incomplete, I would need to merge that big file with a couple of other SHP-files. Unfortunately this does not work in QGIS, it keeps crashing (minidump). I suppose it's because of the file format (not able to handle that amount of data). So I thought maybe it would be possible to add these SHP-files to a Spatialite DB in QGIS and then merge them there somehow. But I don't know exactly how to continue. Maybe there is an easier way to achieve the result
Question: Is there a way to merge these (SHP-)files in QGIS-Spatialite or just QGIS so I can use them with other Layers (SHP-files) for exampling for clipping? I know that theoretically I could use the SHP-files that I want to clip with other SHP-layers one by one, but it would be nicer to have all the data in one layer/file/DB and only clip once. All the SHP-files contain polygons. Edit: Basically the goal is to be able to geoprocess the data comfortably (clip, difference, etc.).
Below is some information from the attribute table from two huge SHP-files that I would like to merge (Merging SHP in Qgis does not work, it crashes):
SHP-file 1: Has one row, file size is 700 kB SHP-file 2:Around 35,000 rows, file size is ~ 400 MB
Important Edit 14.8.18:
So, now I loaded all the many and partly big SHP-files (or the data from them) into a Spatialite data base (or a *.sqlite file). I have them there, I guess they are called "tables" now? I still would like to join/merge/dissolve (what's the right word?) all these different layers/tables into one layer/table that I can use to run geoprocessing commands like clip or difference with another layer in QGIS (in this case a SHP-file layer). I could do it one by one and use the result layer for each layer/table, but the goal is to have it done in one round. I thought that's what all this fancy software is made for? If it helps all the tables/files/layers in my Spatialite DB contain a "geom" -column that says "MULTIPOLYGON" in each row.
I try to do something with st-Union as described for example here, but I can't get it to work. Can anybody help or give a hint?
Edit 15.8.18: I was able to merge two layers in Spatialite that contain the same amount of columns with this SQL code (found it here):
CREATE TABLE merged AS SELECT * FROM layer1 UNION ALL SELECT * FROM layer2;
But I still have other layers that I want to merge and they have a different number of columns which creates this error: "SELECTs to the left and right of UNION ALL do not have the same number of result columns".
Also I'm not sure how to add the other layers, I tried this code and then got the error message aobve:
CREATE TABLE merged AS SELECT * FROM layer1 UNION ALL SELECT * FROM layer2 UNION ALL Select * FROM layer3;
The final layer (merged from all the individual layers) can continue all columns. Important is that it can be used with QGIS' geo-processing tools with other (SHP)-layers.