aliyun/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