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The Databas CLI provides both an interactive REPL (Read-Eval-Print Loop) and a single-query execution mode for testing and exploring SQL queries.

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Installation

Build the CLI from the workspace root: 
cargo build --package databas_cli
The binary will be available at target/debug/databas_cli.

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Usage Modes

The CLI supports two modes of operation:

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Interactive REPL Mode

Launch the REPL by running the CLI without arguments: 
./target/debug/databas_cli
You’ll see the interactive prompt: 
>>>
1

Start the REPL

Run the CLI without arguments to enter interactive mode:
./target/debug/databas_cli
2

Enter SQL queries

Type your SQL queries at the prompt and press Enter:
>>> SELECT * FROM users WHERE id = 1
3

Exit the REPL

Type exit to quit the interactive session:
>>> exit

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Single-Query Mode

Execute a single query by passing it as a command-line argument: 
./target/debug/databas_cli "SELECT * FROM users"
This mode is useful for scripting or quick one-off queries.

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Example Sessions

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Basic Query Execution

$ ./target/debug/databas_cli
>>> SELECT name, email FROM users WHERE age > 18
'SELECT name, email FROM users WHERE age > 18'

>>>
The CLI parses your query and displays the parsed result. Each successfully parsed statement is echoed back in quotes.

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Multiple Statements

You can execute queries with multiple statements: 
>>> CREATE TABLE users (id INTEGER, name TEXT); INSERT INTO users VALUES (1, 'Alice')
'CREATE TABLE users (id INTEGER, name TEXT)'
'INSERT INTO users VALUES (1, 'Alice')'

>>>

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Error Handling

If a query contains syntax errors, the CLI displays an error message: 
>>> SELECT * FORM users
ERROR: expected FROM, got FORM
>>>
The error is displayed on stderr, and the REPL continues running, allowing you to correct and retry your query.

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Exiting the CLI

To exit the interactive REPL, type the exit command: 
>>> exit
$

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Command Reference

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Interactive Commands

CommandDescription
exitExit the interactive REPL session
Any SQL queryParse and display the query structure

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Command-Line Arguments

databas_cli [QUERY]
Arguments:
  • QUERY (optional): SQL query to execute in single-query mode. If omitted, launches the interactive REPL.

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How It Works

The CLI uses the databas_sql_parser crate to parse SQL queries. The parsing process:
  1. Reads input from stdin (REPL mode) or command-line argument (single-query mode)
  2. Passes the query to the SQL parser
  3. Iterates through parsed statements
  4. Displays each successfully parsed statement or shows parsing errors
The current implementation focuses on parsing and validation. Query execution will be added as the database engine matures.

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Tips

  • Press Ctrl+C to force-quit the REPL if needed
  • The CLI outputs to stdout for successful parses and stderr for errors
  • Quote your queries in single-query mode to preserve spacing and special characters
  • Each query in the REPL is independent—there’s no persistent state between queries yet

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Next Steps

SQL Parser

Learn about the SQL parsing engine

Core Database

Explore the database engine internals

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