Question

I just saw a sqlite query and I cannot find what is it mean on the Internet.

                SELECT _id," +
                "NULL AS data1," +
                "NULL AS data2," +
                "artist_key||' '||album_key AS match from ....
                           ^^^^^^^

Are there anyone know what is ||’ ‘|| mean?

Answer 1

|| is the string concatenation operator. From the documenation:

The || operator is “concatenate” – it joins together the two strings
of its operands.

So in your case, the column match in the result will contain the artist_key column joined with the album_key column, with a space in-between.