tessl/pypi-polars-u64-idx

Blazingly fast DataFrame library with 64-bit index support for handling datasets with more than 4.2 billion rows

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SQL Interface

Name: tessl/pypi-polars-u64-idx
Author: tessl

SQL query interface allowing standard SQL operations on DataFrames and integration with existing SQL workflows. Polars provides a comprehensive SQL engine that supports most standard SQL features while maintaining the performance characteristics of the native API.

Capabilities

SQLContext Class

Context manager for executing SQL queries against registered DataFrames and LazyFrames.

class SQLContext:
    def __init__(self, frames: dict[str, DataFrame | LazyFrame] | None = None, **named_frames: DataFrame | LazyFrame):
        """
        Create SQL execution context.
        
        Parameters:
        - frames: Dictionary mapping table names to DataFrames/LazyFrames
        - named_frames: Named DataFrames/LazyFrames as keyword arguments
        
        Examples:
        ctx = SQLContext({"users": df1, "orders": df2})
        ctx = SQLContext(users=df1, orders=df2)
        """
    
    def execute(self, query: str, *, eager: bool = True) -> DataFrame | LazyFrame:
        """
        Execute SQL query.
        
        Parameters:
        - query: SQL query string
        - eager: Return DataFrame (True) or LazyFrame (False)
        
        Returns:
        Query result as DataFrame or LazyFrame
        
        Examples:
        result = ctx.execute("SELECT * FROM users WHERE age > 25")
        lazy_result = ctx.execute("SELECT * FROM users", eager=False)
        """
    
    def register(self, name: str, frame: DataFrame | LazyFrame) -> SQLContext:
        """
        Register DataFrame/LazyFrame as table.
        
        Parameters:
        - name: Table name for SQL queries
        - frame: DataFrame or LazyFrame to register
        
        Returns:
        Self for method chaining
        
        Examples:
        ctx.register("customers", customer_df)
        """
    
    def unregister(self, name: str) -> SQLContext:
        """
        Remove registered table.
        
        Parameters:
        - name: Table name to remove
        
        Returns:
        Self for method chaining
        
        Examples:
        ctx.unregister("temp_table")
        """
    
    def tables(self) -> list[str]:
        """
        Get list of registered table names.
        
        Returns:
        List of table names
        """

SQL Function

Standalone function for executing SQL queries with inline table registration.

def sql(query: str, *, eager: bool = True, **named_frames: DataFrame | LazyFrame) -> DataFrame | LazyFrame:
    """
    Execute SQL query with inline table registration.
    
    Parameters:
    - query: SQL query string
    - eager: Return DataFrame (True) or LazyFrame (False)
    - named_frames: DataFrames/LazyFrames to use as tables
    
    Returns:
    Query result as DataFrame or LazyFrame
    
    Examples:
    result = pl.sql("SELECT * FROM users WHERE age > 25", users=df)
    result = pl.sql("SELECT u.name, o.amount FROM users u JOIN orders o ON u.id = o.user_id", users=users_df, orders=orders_df)
    """

def sql_expr(sql: str) -> Expr:
    """
    Create expression from SQL fragment.
    
    Parameters:  
    - sql: SQL expression string
    
    Returns:
    Expression object
    
    Examples:
    expr = pl.sql_expr("CASE WHEN age > 18 THEN 'Adult' ELSE 'Minor' END")
    df.with_columns(expr.alias("category"))
    """

Supported SQL Features

SELECT Statements

Standard SELECT syntax with column selection, aliases, and expressions.

-- Basic selection
SELECT name, age FROM users;

-- Column aliases
SELECT name AS full_name, age * 12 AS age_months FROM users;

-- Expressions and functions
SELECT 
    name,
    UPPER(name) AS name_upper,
    age + 1 AS next_year_age,
    CASE WHEN age >= 18 THEN 'Adult' ELSE 'Minor' END AS category
FROM users;

-- All columns
SELECT * FROM users;

-- Distinct values
SELECT DISTINCT department FROM employees;

WHERE Clauses

Filtering with various conditions and operators.

-- Simple conditions
SELECT * FROM users WHERE age > 25;
SELECT * FROM users WHERE name = 'John';
SELECT * FROM users WHERE active = true;

-- Multiple conditions
SELECT * FROM users WHERE age > 18 AND age < 65;
SELECT * FROM users WHERE department = 'Sales' OR department = 'Marketing';

-- IN and NOT IN
SELECT * FROM users WHERE department IN ('Sales', 'Marketing', 'Support');
SELECT * FROM users WHERE age NOT IN (25, 30, 35);

-- BETWEEN
SELECT * FROM sales WHERE amount BETWEEN 1000 AND 5000;

-- LIKE patterns
SELECT * FROM users WHERE name LIKE 'John%';
SELECT * FROM users WHERE email LIKE '%@company.com';

-- NULL handling
SELECT * FROM users WHERE phone IS NOT NULL;
SELECT * FROM users WHERE notes IS NULL;

JOINs

Various types of joins between tables.

-- INNER JOIN
SELECT u.name, o.amount 
FROM users u 
INNER JOIN orders o ON u.id = o.user_id;

-- LEFT JOIN
SELECT u.name, o.amount 
FROM users u 
LEFT JOIN orders o ON u.id = o.user_id;

-- RIGHT JOIN
SELECT u.name, o.amount 
FROM users u 
RIGHT JOIN orders o ON u.id = o.user_id;

-- FULL OUTER JOIN
SELECT u.name, o.amount 
FROM users u 
FULL OUTER JOIN orders o ON u.id = o.user_id;

-- Multiple joins
SELECT u.name, o.amount, p.name AS product_name
FROM users u
JOIN orders o ON u.id = o.user_id
JOIN products p ON o.product_id = p.id;

-- Self join
SELECT u1.name AS user1, u2.name AS user2
FROM users u1
JOIN users u2 ON u1.manager_id = u2.id;

GROUP BY and Aggregations

Grouping data with aggregate functions.

-- Basic grouping
SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department;

-- Multiple aggregations
SELECT 
    department,
    COUNT(*) AS count,
    AVG(salary) AS avg_salary,
    MAX(salary) AS max_salary,
    MIN(salary) AS min_salary,
    SUM(salary) AS total_salary
FROM employees
GROUP BY department;

-- Multiple grouping columns
SELECT department, location, COUNT(*) AS count
FROM employees
GROUP BY department, location;

-- HAVING clause
SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;

ORDER BY

Sorting query results.

-- Single column ascending
SELECT * FROM users ORDER BY age;

-- Single column descending  
SELECT * FROM users ORDER BY age DESC;

-- Multiple columns
SELECT * FROM users ORDER BY department, age DESC;

-- Order by expression
SELECT name, age, salary FROM employees ORDER BY salary / age DESC;

-- Order by column position
SELECT name, age FROM users ORDER BY 2 DESC;

LIMIT and OFFSET

Limiting and paginating results.

-- Limit results
SELECT * FROM users LIMIT 10;

-- Offset and limit (pagination)
SELECT * FROM users ORDER BY id LIMIT 10 OFFSET 20;

-- Top N results
SELECT * FROM sales ORDER BY amount DESC LIMIT 5;

Subqueries

Nested queries for complex operations.

-- Subquery in WHERE
SELECT * FROM users 
WHERE department IN (
    SELECT department FROM departments WHERE budget > 100000
);

-- Correlated subquery
SELECT u.name, u.salary
FROM users u
WHERE u.salary > (
    SELECT AVG(salary) FROM users u2 WHERE u2.department = u.department
);

-- Subquery in SELECT
SELECT 
    name,
    salary,
    (SELECT AVG(salary) FROM users) AS company_avg
FROM users;

-- EXISTS
SELECT * FROM users u
WHERE EXISTS (
    SELECT 1 FROM orders o WHERE o.user_id = u.id
);

Window Functions

Advanced analytical functions with window specifications.

-- Row number
SELECT 
    name, 
    salary,
    ROW_NUMBER() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;

-- Partition by
SELECT 
    name,
    department,
    salary,
    ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) AS dept_rank
FROM employees;

-- Aggregate window functions
SELECT 
    name,
    salary,
    SUM(salary) OVER (ORDER BY salary) AS running_total,
    AVG(salary) OVER (PARTITION BY department) AS dept_avg
FROM employees;

-- LAG and LEAD
SELECT 
    date,
    sales,
    LAG(sales, 1) OVER (ORDER BY date) AS prev_sales,
    LEAD(sales, 1) OVER (ORDER BY date) AS next_sales
FROM daily_sales;

Common Table Expressions (CTEs)

WITH clauses for complex queries.

-- Simple CTE
WITH high_earners AS (
    SELECT * FROM employees WHERE salary > 80000
)
SELECT department, COUNT(*) 
FROM high_earners 
GROUP BY department;

-- Multiple CTEs
WITH 
sales_summary AS (
    SELECT user_id, SUM(amount) AS total_sales
    FROM orders
    GROUP BY user_id
),
user_categories AS (
    SELECT 
        user_id,
        CASE 
            WHEN total_sales > 10000 THEN 'VIP'
            WHEN total_sales > 5000 THEN 'Premium'
            ELSE 'Standard'
        END AS category
    FROM sales_summary
)
SELECT category, COUNT(*) AS user_count
FROM user_categories
GROUP BY category;

-- Recursive CTE (if supported)
WITH RECURSIVE subordinates AS (
    SELECT id, name, manager_id, 1 as level
    FROM employees
    WHERE manager_id IS NULL
    
    UNION ALL
    
    SELECT e.id, e.name, e.manager_id, s.level + 1
    FROM employees e
    JOIN subordinates s ON e.manager_id = s.id
)
SELECT * FROM subordinates;

Data Types and Functions

SQL functions and type operations.

-- String functions
SELECT 
    UPPER(name) AS name_upper,
    LOWER(name) AS name_lower,
    LENGTH(name) AS name_length,
    SUBSTRING(name, 1, 3) AS name_prefix,
    CONCAT(first_name, ' ', last_name) AS full_name
FROM users;

-- Numeric functions
SELECT 
    ROUND(salary, -3) AS salary_rounded,
    ABS(balance) AS balance_abs,
    CEIL(rating) AS rating_ceil,
    FLOOR(rating) AS rating_floor
FROM accounts;

-- Date functions
SELECT 
    EXTRACT(YEAR FROM created_at) AS year,
    EXTRACT(MONTH FROM created_at) AS month,
    DATE_TRUNC('month', created_at) AS month_start,
    created_at + INTERVAL '30 days' AS future_date
FROM orders;

-- Conditional functions
SELECT 
    name,
    CASE 
        WHEN age < 18 THEN 'Minor'
        WHEN age < 65 THEN 'Adult'
        ELSE 'Senior'
    END AS age_category,
    COALESCE(phone, email, 'No contact') AS contact_info,
    NULLIF(status, 'inactive') AS active_status
FROM users;

Usage Examples

Basic SQL Operations

import polars as pl

# Create sample data
users = pl.DataFrame({
    "id": [1, 2, 3, 4, 5],
    "name": ["Alice", "Bob", "Charlie", "Diana", "Eve"],
    "age": [25, 30, 35, 28, 32],
    "department": ["Sales", "Engineering", "Sales", "Marketing", "Engineering"]
})

orders = pl.DataFrame({
    "id": [101, 102, 103, 104, 105],
    "user_id": [1, 2, 1, 3, 2],
    "amount": [100, 250, 150, 300, 200],
    "date": ["2023-01-15", "2023-01-16", "2023-01-17", "2023-01-18", "2023-01-19"]
})

# Simple SQL query
result = pl.sql("""
    SELECT name, age, department
    FROM users 
    WHERE age > 30
    ORDER BY age DESC
""", users=users)

print(result)

Using SQLContext

# Create SQL context with multiple tables
ctx = pl.SQLContext({
    "users": users,
    "orders": orders
})

# Complex query with joins
result = ctx.execute("""
    SELECT 
        u.name,
        u.department,
        COUNT(o.id) as order_count,
        SUM(o.amount) as total_spent,
        AVG(o.amount) as avg_order
    FROM users u
    LEFT JOIN orders o ON u.id = o.user_id
    GROUP BY u.id, u.name, u.department
    ORDER BY total_spent DESC
""")

# Register additional tables
products = pl.DataFrame({
    "id": [1, 2, 3],
    "name": ["Widget", "Gadget", "Tool"],
    "category": ["A", "B", "A"]
})

ctx.register("products", products)

Advanced SQL Features

# Window functions
result = ctx.execute("""
    SELECT 
        name,
        department,
        age,
        ROW_NUMBER() OVER (PARTITION BY department ORDER BY age) as dept_rank,
        AVG(age) OVER (PARTITION BY department) as dept_avg_age,
        age - AVG(age) OVER (PARTITION BY department) as age_diff
    FROM users
""")

# CTE with aggregations
result = ctx.execute("""
    WITH department_stats AS (
        SELECT 
            department,
            COUNT(*) as emp_count,
            AVG(age) as avg_age,
            MAX(age) as max_age
        FROM users
        GROUP BY department
    ),
    order_stats AS (
        SELECT 
            u.department,
            SUM(o.amount) as dept_sales
        FROM users u
        JOIN orders o ON u.id = o.user_id
        GROUP BY u.department
    )
    SELECT 
        ds.department,
        ds.emp_count,
        ds.avg_age,
        COALESCE(os.dept_sales, 0) as total_sales,
        COALESCE(os.dept_sales, 0) / ds.emp_count as sales_per_employee
    FROM department_stats ds
    LEFT JOIN order_stats os ON ds.department = os.department
    ORDER BY sales_per_employee DESC
""")

Mixing SQL with Polars API

# Start with SQL, continue with Polars API
lazy_result = pl.sql("""
    SELECT u.name, u.department, o.amount, o.date
    FROM users u
    JOIN orders o ON u.id = o.user_id
    WHERE u.age > 25
""", users=users, orders=orders, eager=False)

# Continue with Polars operations
final_result = (lazy_result
    .with_columns([
        pl.col("date").str.strptime(pl.Date, "%Y-%m-%d"),
        pl.col("amount").cast(pl.Float64)
    ])
    .filter(pl.col("amount") > 150)
    .group_by("department")
    .agg([
        pl.col("amount").sum().alias("total_sales"),
        pl.col("name").n_unique().alias("unique_customers")
    ])
    .collect()
)

SQL Expression Integration

# Use SQL expressions in Polars operations
df = users.with_columns([
    pl.sql_expr("CASE WHEN age >= 30 THEN 'Senior' ELSE 'Junior' END").alias("seniority"),
    pl.sql_expr("UPPER(name)").alias("name_upper"),
    pl.sql_expr("age * 12").alias("age_months")
])

# Complex SQL expressions
df = users.with_columns([
    pl.sql_expr("""
        CASE 
            WHEN department = 'Engineering' AND age > 30 THEN 'Senior Engineer'
            WHEN department = 'Engineering' THEN 'Engineer'
            WHEN department = 'Sales' AND age > 28 THEN 'Senior Sales'
            WHEN department = 'Sales' THEN 'Sales Rep'
            ELSE 'Other'
        END
    """).alias("role")
])

Performance Optimization

# Lazy execution with SQL
lazy_query = pl.sql("""
    SELECT 
        department,
        COUNT(*) as count,
        AVG(age) as avg_age
    FROM users
    WHERE age > 25
    GROUP BY department
""", users=users.lazy(), eager=False)

# Check execution plan
print(lazy_query.explain())

# Collect with optimizations
result = lazy_query.collect(
    predicate_pushdown=True,
    projection_pushdown=True
)

Error Handling

try:
    result = ctx.execute("SELECT * FROM nonexistent_table")
except pl.SQLSyntaxError as e:
    print(f"SQL syntax error: {e}")
except pl.SQLInterfaceError as e:
    print(f"SQL interface error: {e}")
except Exception as e:
    print(f"Other error: {e}")