I agree.
However, there is a another step in-between text and database, in the form of a "Foreign Data Wrapper", to let the database serve up the underlying (csv-)textfile:
psql -qX << SQL_TXT
create server if not exists temp_fs foreign data wrapper file_fdw;
drop foreign table if exists ft_pm2 cascade;
create foreign table ft_pm2 (
"CAT_HEADER" text
, "SUPPLIER_CODE" text
, "CUSTOMER_CODE" text
, "F4" text
, "F5" text
, "F6" text
, "F7" text
, "F8" numeric
)
server temp_fs
options (
format 'csv'
, header 'true'
, filename '/tmp/data.txt'
);
copy(select * from ft_pm2 order by 2, 3) to stdout with (format csv, h
+eader true);
SQL_TXT
Results are (again):
CAT_HEADER,SUPPLIER_CODE,CUSTOMER_CODE,F4,F5,F6,F7,F8
CAT_LINE,0001P,ABC12345,20190924,,1,Z,3.36
CAT_LINE,0001P,ABC23456,20190924,,1,Z,2.14
CAT_LINE,0001P,ABC34567,20190924,,1,Z,12.23
CAT_LINE,0002P,ABC12345,20190924,,1,Z,4.26
CAT_LINE,0002P,ABC23456,20190924,,1,Z,1.21
CAT_LINE,0002P,ABC34567,20190924,,1,Z,22.24
Such SQL using a 'Foreign Table' reads the underlying csv/text file(s). The annoying part is setting up the table , for instance in the case of tables with hundreds of columns you need a separate little application to do that, and this is where perl comes in handy (reading the header line and turning it into the CREATE TABLE column-list).
Weaknesses and strengths:
Advantages: SQL access to csv data. DBD::CSV delivers SQL as in
SQL::Statement::Syntax
which is nice but basic. The Data Wrapper's Foreign Table gives you access to the data via the full postgres SQL engine:
Window Functions,
Grouping Sets/Cube/Rollup,
Generated Columns,
Partitioning
, etc., etc.)
Disadvantages: Needs Postgres, and with extension file_fdw installed. Table remains read-only. No indexing possible, so that huge csv-files can make it slow (alhough 'copying' onto a materialized view [3] on the foreign table makes of course indexing possible again). Filesystem access for the postgres superuser is necessary.
It all depends what you want to do.
[1] file_fdw - this foreign data wrapper reads text files
[2] Create Server
[3] Create Foreign Table
[4] Create Materialized View
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