Copying CSV file to temp table with dynamic number of columns?
Basics:


The 1st row of the CSV file has column names of defined format.
The PROGRAM clause of COPY and GET DIAGNOSTICS after COPY require Postgres 9.3+.
format() requires Postgres 9.1+
This works with pure standard Postgres - except for the head command that the shell is expected to provide. For Windows versions consider:


How to do what head, tail, more, less, sed do in Powershell?



Full automation

This function copies any table structure completely dynamically:

CREATE OR REPLACE FUNCTION f_dynamic_copy(_file    text
                                        , _tbl     text = 'tmp1'
                                        , _delim   text = E'\t'
                                        , _nodelim text = chr(127)) -- see below!
  RETURNS text AS
$func$
DECLARE
   row_ct int;
BEGIN
   -- create staging table for 1st row as  single text column 
   CREATE TEMP TABLE tmp0(cols text) ON COMMIT DROP;

   -- fetch 1st row
   EXECUTE format($$COPY tmp0 FROM PROGRAM 'head -n1 %I' WITH (DELIMITER %L)$$  -- impossible delimiter
                , _file, _nodelim);

   -- create actual temp table with all columns text
   EXECUTE (
      SELECT format('CREATE TEMP TABLE %I(', _tbl)
          || string_agg(quote_ident(col) || ' text', ',')
          || ')'
      FROM  (SELECT cols FROM tmp0 LIMIT 1) t
           , unnest(string_to_array(t.cols, E'\t')) col
      );

   -- Import data
   EXECUTE format($$COPY %I FROM %L WITH (FORMAT csv, HEADER, NULL '\N', DELIMITER %L)$$
                , _tbl, _file, _delim);

   GET DIAGNOSTICS row_ct = ROW_COUNT;
   RETURN format('Created table %I with %s rows.', _tbl, row_ct);
END
$func$  LANGUAGE plpgsql;


Call variants:

SELECT f_dynamic_copy('/path/to/file.csv');
SELECT f_dynamic_copy('/path/to/file2.csv', 'tmp_file2');
SELECT f_dynamic_copy(_file  =&gt; '/path/to/file2.csv'
                    , _tbl   =&gt; 'tmp_file2');
                    , _delim =&gt; E'\t'); -- using assignment operator since pg 9.5


Answer:

Created table tmp_file2 with 123 rows.

Before the main COPY, run a preliminary COPY ... TO tmp0 to fetch the first row with column names, which are expected to be unquoted, case-sensitive strings like COPY ... TO ... (FORMAT csv, HEADER) would export them. 

The structure of the actual target table is derived from it, all columns with data type text. The default name of the resulting table is tmp1 - or provide your own as 2nd function parameter.

Then COPY is executed. The default delimiter is a tab character - or provide your delimiter as 3rd function parameter.

Use any single-byte character for the non-delimiter _nodelim which does not appear in the first line of your CSV file. I am arbitrarily picking the control character "Delete" (ASCII 127). That character would be swallowed here on SO, so I generate with chr(127) instead, which is also valid. Assuming the character won't pop up - or provide your non-delimiter as 4th function parameter.

The function returns table name and number of imported rows.
Remember, a temporary table dies with the end of the session.

The manual:


  Executing a command with PROGRAM might be restricted by the operating
  system's access control mechanisms, such as SELinux.


Related answer on SO:


“ERROR: extra data after last expected column” when using PostgreSQL COPY


Postgres 8.4

That version is too old, I am not going to back-port that far.


GET DIAGNOSTICS  is an optional feature. You can just leave it away or replace it with a full count on the table
A primitive (expensive) alternative for the PROGRAM clause of COPY in pg 9.3 would be to import the complete table instead:

EXECUTE format($$COPY tmp0 FROM %L WITH (DELIMITER %L)$$, _file, _delim);



Or you prepare a second input file, or you can make it work by piping from the shell: COPY tablename FROM STDIN is available in pg 8.4.


format() can be replaced with plain string concatenation. Be wary of SQL injection though!


SQL injection in Postgres functions vs prepared queries