duckdb-en

DuckDB CLI Specialist

Helps with data analysis, SQL queries and file conversion via DuckDB CLI.

Quick Start

Read data files directly with SQL

# CSV
duckdb -c "SELECT * FROM 'data.csv' LIMIT 10"

# Parquet
duckdb -c "SELECT * FROM 'data.parquet'"

# Multiple files with glob
duckdb -c "SELECT * FROM read_parquet('logs/*.parquet')"

# JSON
duckdb -c "SELECT * FROM read_json_auto('data.json')"

Open persistent databases

# Create/open database
duckdb my_database.duckdb

# Read-only mode
duckdb -readonly existing.duckdb

Command Line Arguments

Output formats (as flags)

Flag	Format
-csv	Comma-separated
-json	JSON array
-table	ASCII table
-markdown	Markdown table
-html	HTML table
-line	One value per line

Execution arguments

Argument	Description
-c COMMAND	Run SQL and exit
-f FILENAME	Run script from file
-init FILE	Use alternative to ~/.duckdbrc
-readonly	Open in read-only mode
-echo	Show commands before execution
-bail	Stop on first error
-header / -noheader	Show/hide column headers
-nullvalue TEXT	Text for NULL values
-separator SEP	Column separator

Data Conversion

CSV to Parquet

duckdb -c "COPY (SELECT * FROM 'input.csv') TO 'output.parquet' (FORMAT PARQUET)"

Parquet to CSV

duckdb -c "COPY (SELECT * FROM 'input.parquet') TO 'output.csv' (HEADER, DELIMITER ',')"

JSON to Parquet

duckdb -c "COPY (SELECT * FROM read_json_auto('input.json')) TO 'output.parquet' (FORMAT PARQUET)"

Convert with filtering

duckdb -c "COPY (SELECT * FROM 'data.csv' WHERE amount > 1000) TO 'filtered.parquet' (FORMAT PARQUET)"

Dot Commands

Schema inspection

Command	Description
.tables [pattern]	Show tables (with LIKE pattern)
.schema [table]	Show CREATE statements
.databases	Show attached databases

Output control

Command	Description
.mode FORMAT	Change output format
.output file	Send output to file
.once file	Next output to file
.headers on/off	Show/hide column headers
.separator COL ROW	Set separators

Queries

Command	Description
.timer on/off	Show execution time
.echo on/off	Show commands before execution
.bail on/off	Stop on error
.read file.sql	Run SQL from file

Editing

Command	Description
.edit or \e	Open query in external editor
.help [pattern]	Show help

Output Formats (18 available)

Data export

• csv - Comma-separated for spreadsheets
• tabs - Tab-separated
• json - JSON array
• jsonlines - Newline-delimited JSON (streaming)

Readable formats

• duckbox (default) - Pretty ASCII with unicode box-drawing
• table - Simple ASCII table
• markdown - For documentation
• html - HTML table
• latex - For academic papers

Specialized

• insert TABLE - SQL INSERT statements
• column - Columns with adjustable width
• line - One value per line
• list - Pipe-separated
• trash - Discard output

Keyboard Shortcuts (macOS/Linux)

Navigation

Shortcut	Action
Home / End	Start/end of line
Ctrl+Left/Right	Jump word
Ctrl+A / Ctrl+E	Start/end of buffer

History

Shortcut	Action
Ctrl+P / Ctrl+N	Previous/next command
Ctrl+R	Search history
Alt+< / Alt+>	First/last in history

Editing

Shortcut	Action
Ctrl+W	Delete word backward
Alt+D	Delete word forward
Alt+U / Alt+L	Uppercase/lowercase word
Ctrl+K	Delete to end of line

Autocomplete

Shortcut	Action
Tab	Autocomplete / next suggestion
Shift+Tab	Previous suggestion
Esc+Esc	Undo autocomplete

Autocomplete

Context-aware autocomplete activated with Tab:

• Keywords - SQL commands
• Table names - Database objects
• Column names - Fields and functions
• File names - Path completion

Database Operations

Create table from file

CREATE TABLE sales AS SELECT * FROM 'sales_2024.csv';

Insert data

INSERT INTO sales SELECT * FROM 'sales_2025.csv';

Export table

COPY sales TO 'backup.parquet' (FORMAT PARQUET);

Analysis Examples

Quick statistics

SELECT
    COUNT(*) as count,
    AVG(amount) as average,
    SUM(amount) as total
FROM 'transactions.csv';

Grouping

SELECT
    category,
    COUNT(*) as count,
    SUM(amount) as total
FROM 'data.csv'
GROUP BY category
ORDER BY total DESC;

Join on files

SELECT a.*, b.name
FROM 'orders.csv' a
JOIN 'customers.parquet' b ON a.customer_id = b.id;

Describe data

DESCRIBE SELECT * FROM 'data.csv';

Pipe and stdin

# Read from stdin
cat data.csv | duckdb -c "SELECT * FROM read_csv('/dev/stdin')"

# Pipe to another command
duckdb -csv -c "SELECT * FROM 'data.parquet'" | head -20

# Write to stdout
duckdb -c "COPY (SELECT * FROM 'data.csv') TO '/dev/stdout' (FORMAT CSV)"

Configuration

Save common settings in ~/.duckdbrc:

.timer on
.mode duckbox
.maxrows 50
.highlight on

Syntax highlighting colors

.keyword green
.constant yellow
.comment brightblack
.error red

External Editor

Open complex queries in your editor:

.edit

Editor is chosen from: DUCKDB_EDITOR → EDITOR → VISUAL → vi

Safe Mode

Secure mode that restricts file access. When enabled:

• No external file access
• Disables .read, .output, .import, .sh etc.
• Cannot be disabled in the same session

Tips

• Use LIMIT on large files for quick preview
• Parquet is faster than CSV for repeated queries
• read_csv_auto and read_json_auto guess column types
• Arguments are processed in order (like SQLite CLI)
• WSL2 may show incorrect memory_limit values on some Ubuntu versions