SQL server Openquery equivalent to PostgresQL - postgresql

Question

Is there query equivalent to sql server's openquery or openrowset to use in postgresql to query from excel or csv ?

Answer 1

You can use PostgreSQL's COPY
As per doc:
COPY moves data between PostgreSQL tables and standard file-system
files. COPY TO copies the contents of a table to a file, while COPY
FROM copies data from a file to a table (appending the data to
whatever is in the table already). COPY TO can also copy the results
of a SELECT query
COPY works like this:
Importing a table from CSV
Assuming you already have a table in place with the right columns, the command is as follows
COPY tblemployee FROM '~/empsource.csv' DELIMITERS ',' CSV;
Exporting a CSV from a table.
COPY (select * from tblemployee) TO '~/exp_tblemployee.csv' DELIMITERS ',' CSV;
Its important to mention here that generally if your data is in unicode or need strict Encoding, then Always set client_encoding before running any of the above mentioned commands.
To set CLIENT_ENCODING parameter in PostgreSQL
set client_encoding to 'UTF8'
or
set client_encoding to 'latin1'
Another thing to guard against is nulls, while exporting , if some fields are null then PostgreSQL will add '/N' to represent a null field, this is fine but may cause issues if you are trying to import that data in say SQL server.
A quick fix is modify the export command by specifying what would you prefer as a null placeholder in exported CSV
COPY (select * from tblemployee ) TO '~/exp_tblemployee.csv' DELIMITERS ',' NULL as E'';
Another common requirement is import or export with the header.
Import CSV to table with Header for columns present in first row of csv file.
COPY tblemployee FROM '~/empsource.csv' DELIMITERS ',' CSV HEADER
Export a table to CSV with Headers present in the first row.
COPY (select * from tblemployee) TO '~/exp_tblemployee.csv' DELIMITERS ',' CSV HEADER