SyntaxShelf

Union

2 snippets across 2 stacks - Python, SQL

Also written as Union · union all

PYPython

typing Module Essentials

PY · Common Standard Library
Syntax
from typing import Optional, Union, TypeVar, Generic
Example
from typing import TypeVar, Generic

T = TypeVar("T")

class Stack(Generic[T]):
    def __init__(self) -> None:
        self._items: list[T] = []

    def push(self, item: T) -> None:
        self._items.append(item)

    def pop(self) -> T:
        return self._items.pop()

stack = Stack[int]()
stack.push(42)
print(stack.pop())
Output
42

Note Since 3.10, use X | Y instead of Union[X, Y]. Since 3.12, use the type parameter syntax: class Stack[T]: instead of TypeVar + Generic.

SQLSQL

UNION / UNION ALL

SQL · Advanced
Syntax
SELECT columns FROM table1
UNION [ALL]
SELECT columns FROM table2;
Example
SELECT first_name, email, 'customer' AS source
FROM customers
UNION ALL
SELECT first_name, email, 'employee' AS source
FROM employees;
Output
-- Combined list of customers and employees

Note UNION removes duplicates (slower, requires sorting). UNION ALL keeps all rows (faster). Use UNION ALL unless you specifically need deduplication. Both queries must have the same number of columns with compatible types.

Frequently asked questions

How does Python handle union?
This task is covered in 2 stacks on this page: Python, SQL. The "typing Module Essentials" snippet in Python uses `from typing import Optional, Union, TypeVar, Generic`.
Which code does the Python example use?
The "typing Module Essentials" snippet uses `from typing import Optional, Union, TypeVar, Generic`, from the Common Standard Library section of the Python cheat sheet.
Which stacks cover "union" on this page?
Python, SQL. Together they hold 2 copy-ready snippets for this task.
Is there anything to watch out for?
Yes. For "typing Module Essentials": Since 3.10, use X | Y instead of Union[X, Y]. Since 3.12, use the type parameter syntax: class Stack[T]: instead of TypeVar + Generic.

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