pgloader-usage-examples

Pgloader Usage Examples

Currently not included, because redundant with the tutorial.

Usage Examples

Review the command line options and pgloader’s version:

pgloader --help
pgloader --version

Loading from a complex command

Use the command file as the pgloader command argument, pgloader will parse that file and execute the commands found in it:

pgloader --verbose ./test/csv-districts.load

CSV

Load data from a CSV file into a pre-existing table in your database, having pgloader guess the CSV properties (separator, quote and escape character):

pgloader ./test/data/matching-1.csv pgsql:///pgloader?tablename=matching

Load data from a CSV file into a pre-existing table in your database, with expanded options:

pgloader --type csv                                   \
         --field id --field field                     \
         --with truncate                              \
         --with "fields terminated by ','"            \
         ./test/data/matching-1.csv                   \
         postgres:///pgloader?tablename=matching

In that example the whole loading is driven from the command line, bypassing the need for writing a command in the pgloader command syntax entirely. As there’s no command though, the extra inforamtion needed must be provided on the command line using the –type and –field and –with switches.

For documentation about the available syntaxes for the –field and –with switches, please refer to the CSV section later in the man page.

Note also that the PostgreSQL URI includes the target tablename.

Reading from STDIN

File based pgloader sources can be loaded from the standard input, as in the following example:

pgloader --type csv                                         \
         --field "usps,geoid,aland,awater,aland_sqmi,awater_sqmi,intptlat,intptlong" \
         --with "skip header = 1"                          \
         --with "fields terminated by '\t'"                \
         -                                                 \
         postgresql:///pgloader?districts_longlat          \
         < test/data/2013_Gaz_113CDs_national.txt

The dash (-) character as a source is used to mean standard input, as usual in Unix command lines. It’s possible to stream compressed content to pgloader with this technique, using the Unix pipe:

gunzip -c source.gz | pgloader –type csv … - pgsql:///target?foo

Loading from CSV available through HTTP

The same command as just above can also be run if the CSV file happens to be found on a remote HTTP location:

pgloader --type csv                                                     \
         --field "usps,geoid,aland,awater,aland_sqmi,awater_sqmi,intptlat,intptlong" \
         --with "skip header = 1"                                       \
         --with "fields terminated by '\t'"                             \
         http://pgsql.tapoueh.org/temp/2013_Gaz_113CDs_national.txt     \
         postgresql:///pgloader?districts_longlat

Some more options have to be used in that case, as the file contains a one-line header (most commonly that’s column names, could be a copyright notice). Also, in that case, we specify all the fields right into a single –field option argument.

Again, the PostgreSQL target connection string must contain the tablename option and you have to ensure that the target table exists and may fit the data. Here’s the SQL command used in that example in case you want to try it yourself:

create table districts_longlat
(
         usps        text,
         geoid       text,
         aland       bigint,
         awater      bigint,
         aland_sqmi  double precision,
         awater_sqmi double precision,
         intptlat    double precision,
         intptlong   double precision
);

Also notice that the same command will work against an archived version of the same data, e.g. http://pgsql.tapoueh.org/temp/2013_Gaz_113CDs_national.txt.gz.

Finally, it’s important to note that pgloader first fetches the content from the HTTP URL it to a local file, then expand the archive when it’s recognized to be one, and only then processes the locally expanded file.

In some cases, either because pgloader has no direct support for your archive format or maybe because expanding the archive is not feasible in your environment, you might want to stream the content straight from its remote location into PostgreSQL. Here’s how to do that, using the old battle tested Unix Pipes trick:

curl http://pgsql.tapoueh.org/temp/2013_Gaz_113CDs_national.txt.gz \
| gunzip -c                                                        \
| pgloader --type csv                                              \
           --field "usps,geoid,aland,awater,aland_sqmi,awater_sqmi,intptlat,intptlong"
           --with "skip header = 1"                                \
           --with "fields terminated by '\t'"                      \
           -                                                       \
           postgresql:///pgloader?districts_longlat

Now the OS will take care of the streaming and buffering between the network and the commands and pgloader will take care of streaming the data down to PostgreSQL.

Migrating from SQLite

The following command will open the SQLite database, discover its tables definitions including indexes and foreign keys, migrate those definitions while casting the data type specifications to their PostgreSQL equivalent and then migrate the data over:

createdb newdb
pgloader ./test/sqlite/sqlite.db postgresql:///newdb

Migrating from MySQL

Just create a database where to host the MySQL data and definitions and have pgloader do the migration for you in a single command line:

createdb pagila
pgloader mysql://user@localhost/sakila postgresql:///pagila

Fetching an archived DBF file from a HTTP remote location

It’s possible for pgloader to download a file from HTTP, unarchive it, and only then open it to discover the schema then load the data:

createdb foo
pgloader --type dbf http://www.insee.fr/fr/methodes/nomenclatures/cog/telechargement/2013/dbf/historiq2013.zip postgresql:///foo

Here it’s not possible for pgloader to guess the kind of data source it’s being given, so it’s necessary to use the –type command line switch.