How can i get substring in SQLite? - sqlite

Question

There is a column.
And it has values like
'/abc/def/ghi/w1.xyz'
'/jkl/mno/r.stuv'
(it's path data and the number of '/'s in each value is not fixed.)
how can i get substring column which has values like
'/abc/def/ghi/'
'/jkl/mno/'
(extracting only the directory part. removing the file part.)
i read about substr(X,Y), substr(X,Y,Z), instr(X,Y).
but it's not easy to apply them because the number of '/'s in each value is not fixed and instr(X,Y) seems to find the first occurrence from the left.

Answer 1

With a recursive CTE:
create table tablename(col text);
insert into tablename(col) values
('/abc/def/ghi/w1.xyz'),
('/jkl/mno/r.stuv');
with recursive cte(col, pos, rest) as (
select col, instr(col, '/') pos, substr(col, instr(col, '/') + 1) rest
from tablename
union all
select col, instr(rest, '/'), substr(rest, instr(rest, '/') + 1)
from cte
where instr(rest, '/') > 0
)
select col, substr(col, 1, sum(pos)) path
from cte
group by col
See the demo.
Results:
| col | path |
| ------------------- | ------------- |
| /abc/def/ghi/w1.xyz | /abc/def/ghi/ |
| /jkl/mno/r.stuv | /jkl/mno/ |

Answer 2

If you are on Unix/Linux environment, you could do something like this (let's take an example).
Let's say test.db was your SQLite3 database with a table like so:
create table test (dataset text);
insert into test (dataset) values ('/abc/def/ghi/w1.xyz');
insert into test (dataset) values ('/jkl/mno/r.stuv');
From command line, you can run:
sqlite3 test.db -batch -noheader "select dataset from test"
That'll give you this as the output (I know that's not the output you want, but just read on):
/abc/def/ghi/w1.xyz
/jkl/mno/r.stuv
Explanation
the -batch and -noheader switches suppress all output except for the data resulting from the SQL statement
sqlite3 test.db -batch -noheader "sql statement" runs the SQL statement you provided and the output is dumped on the screen (stdout)
Solution
Now, we'll use awk with it to get what you want like so:
sqlite3 test.db -batch -noheader "select dataset from test" | awk -F'/' 'BEGIN{OFS="/"} {$NF = ""; print $0}'
Result will be:
/abc/def/ghi/
/jkl/mno/
Crude explanation
awk works on every line output by your sqlite3 command
the line is split by / character with -F'/' switch
since we want the output to contain the delimiters as is, we set the output field separator to be '/' as well using OFS='/'
we set number of fields (NF) in a way that the last item is ignored and then we print the rest of the data
as the other split fields are printed, OFS inserts / between those fields