added duckdb import for mimic3 as per #1238

mimic-iii/buildmimic/duckdb/README.md

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+# DuckDB
+
+The script in this folder creates the schema for MIMIC-IV and
+loads the data into the appropriate tables for
+[DuckDB](https://duckdb.org/).
+DuckDB, like SQLite, is serverless and
+stores all information in a single file.
+Unlike SQLite, an OLTP database,
+DuckDB is an OLAP database, and therefore optimized for analytical queries.
+This will result in faster queries for researchers using MIMIC-IV
+with DuckDB compared to SQLite.
+To learn more, please read their ["why duckdb"](https://duckdb.org/docs/why_duckdb)
+page.
+
+The instructions to load MIMIC-III into a DuckDB
+only require:
+1. DuckDB to be installed and
+2. Your computer to have a POSIX-compliant terminal shell,
+   which is already found by default on any Mac OSX, Linux, or BSD installation.
+
+To use these instructions on Windows,
+you need a Unix command line environment,
+which you can obtain by either installing
+[Windows Subsystem for Linux](https://docs.microsoft.com/en-us/windows/wsl/install-win10)
+or [Cygwin](https://www.cygwin.com/).
+
+## Set-up
+
+### Quick overview
+
+1. [Install](https://duckdb.org/docs/installation/) the CLI version of DuckDB
+2. [Download](https://physionet.org/content/mimiciii/1.4/) the MIMIC-III files
+3. Create DuckDB database and load data
+
+### Install DuckDB
+
+Follow instructions on their website to
+[install](https://duckdb.org/docs/installation/)
+the CLI version of DuckDB.
+
+You will need to place the `duckdb` binary in a folder on your environment path,
+e.g. `/usr/local/bin`.
+
+### Download MIMIC-III files
+
+[Download](https://physionet.org/content/mimiciii/1.4/)
+the CSV files for MIMIC-III by any method you wish.
+
+The intructions assume the CSV files are in the folder structure as follows:
+
+```
+mimic_data_dir
+    ADMISSIONS.csv.gz
+    ...
+```
+
+The CSV files can be uncompressed (end in `.csv`) or compressed (end in `.csv.gz`).
+
+The easiest way to download them is to open a terminal then run:
+
+```
+wget -r -N -c -np --user YOURUSERNAME --ask-password https://physionet.org/files/mimiciii/1.4/
+```
+
+Replace `YOURUSERNAME` with your physionet username.
+
+This will make you `mimic_data_dir` be `physionet.org/files/mimiciii/1.4`.
+
+# Create DuckDB database and load data
+
+The last step requires creating a DuckDB database and
+loading the data into it.
+
+You can do all of this will one shell script, `import_duckdb.sh`,
+located in this repository.
+
+See the help for it below:
+
+```sh
+$ ./import_duckdb.sh -h
+./import_duckdb.sh:
+USAGE: ./import_duckdb.sh mimic_data_dir [output_db]
+WHERE:
+    mimic_data_dir        directory that contains csv.gz or csv files
+    output_db: optional   filename for duckdb file (default: mimic3.db)
+$
+```
+
+Here's an example invocation that will make the database in the default "mimic3.db":
+
+```sh
+$ ./import_duckdb.sh physionet.org/files/mimiciii/1.4
+
+... output removed
+Successfully finished loading data into mimic3.db.
+
+$ ls -lh mimic3.db
+-rw-rw-r--. 1 myuser mygroup 26G Jan 25 16:11 mimic3.db
+```
+
+The script will print out progress as it goes.
+Be patient, this can take minutes to hours to load
+depending on your computer's configuration.
+
+# Help
+
+Please see the [issues page](https://github.com/MIT-LCP/mimic-iii/issues) to discuss other issues you may be having.