VARIADIC parameters in PostgreSQL

Introduction

VARIADIC parameters let you pass a flexible number of arguments to a function. This helps when you don't know how many inputs you will get.

When you want a function to accept any number of values, like adding many numbers.

When you want to search for multiple keywords in a text without fixing how many keywords.

When you want to collect a list of items in one call without making many calls.

When you want to simplify your code by handling multiple inputs in one function.

Syntax

PostgreSQL

CREATE FUNCTION function_name(VARIADIC param_name data_type[]) RETURNS return_type AS $$
BEGIN
  -- function body
END;
$$ LANGUAGE plpgsql;

The VARIADIC keyword must be used before the last parameter in the function.

The parameter with VARIADIC must be an array type.

Examples

This function sums any number of integers passed as arguments.

PostgreSQL

CREATE FUNCTION sum_numbers(VARIADIC nums int[]) RETURNS int AS $$
DECLARE
  total int := 0;
  n int;
BEGIN
  FOREACH n IN ARRAY nums LOOP
    total := total + n;
  END LOOP;
  RETURN total;
END;
$$ LANGUAGE plpgsql;

Calls the sum_numbers function with 4 numbers, returns 10.

PostgreSQL

SELECT sum_numbers(1, 2, 3, 4);

This function joins multiple text inputs into one string separated by commas.

PostgreSQL

CREATE FUNCTION concat_texts(VARIADIC texts text[]) RETURNS text AS $$
BEGIN
  RETURN array_to_string(texts, ', ');
END;
$$ LANGUAGE plpgsql;

Returns 'apple, banana, cherry'.

PostgreSQL

SELECT concat_texts('apple', 'banana', 'cherry');

Sample Program

This function greets each name passed to it. If no names are given, it says 'Hello, nobody!'.

PostgreSQL

CREATE FUNCTION greet_people(VARIADIC names text[]) RETURNS text AS $$
DECLARE
  result text := '';
  name text;
BEGIN
  IF array_length(names, 1) IS NULL THEN
    RETURN 'Hello, nobody!';
  END IF;
  FOREACH name IN ARRAY names LOOP
    result := result || 'Hello, ' || name || '! '; 
  END LOOP;
  RETURN trim(result);
END;
$$ LANGUAGE plpgsql;

SELECT greet_people('Alice', 'Bob', 'Charlie');

Important Notes

You can call a VARIADIC function with an array by using VARIADIC keyword in the call, like: SELECT func(VARIADIC array);

VARIADIC parameters must be the last parameter in the function definition.

Summary

VARIADIC lets functions accept flexible numbers of arguments as an array.

Use VARIADIC for cleaner code when input count varies.

Remember VARIADIC parameter must be last and is always an array type.

Practice

1. What does the VARIADIC keyword do in a PostgreSQL function?

easy

A. Specifies that the function is a trigger

B. Defines a function that returns multiple result sets

C. Allows the function to accept a variable number of arguments as an array

D. Indicates the function is immutable

Solution

1. Step 1: Understand the role of VARIADIC

   VARIADIC allows a function to accept any number of arguments as a single array parameter.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated function features.

3. Final Answer:

   Allows the function to accept a variable number of arguments as an array -> Option C

4. Quick Check:

   VARIADIC = variable arguments as array [OK]

Hint: VARIADIC means flexible argument count packed as array [OK]

Common Mistakes:

• Thinking VARIADIC returns multiple result sets
• Confusing VARIADIC with triggers
• Assuming VARIADIC changes function volatility

2. Which of the following is the correct syntax to declare a VARIADIC parameter in a PostgreSQL function?

easy

A. CREATE FUNCTION example(VARIADIC nums int[]) RETURNS int AS $$ ... $$ LANGUAGE sql;

B. CREATE FUNCTION example(nums VARIADIC int) RETURNS int AS $$ ... $$ LANGUAGE sql;

C. CREATE FUNCTION example(nums int VARIADIC) RETURNS int AS $$ ... $$ LANGUAGE sql;

D. CREATE FUNCTION example(nums int[]) VARIADIC RETURNS int AS $$ ... $$ LANGUAGE sql;

Solution

1. Step 1: Identify correct VARIADIC syntax

   VARIADIC must precede the parameter name and the parameter type must be an array type, e.g., VARIADIC nums int[].

2. Step 2: Check each option

   CREATE FUNCTION example(VARIADIC nums int[]) RETURNS int AS $$ ... $$ LANGUAGE sql; correctly places VARIADIC before the parameter name and uses an array type. Options A, B, and C misuse the position or syntax of VARIADIC.

3. Final Answer:

   CREATE FUNCTION example(VARIADIC nums int[]) RETURNS int AS $$ ... $$ LANGUAGE sql; -> Option A

4. Quick Check:

   VARIADIC before param name + array type = correct syntax [OK]

Hint: VARIADIC goes before param name and uses array type [OK]

Common Mistakes:

• Placing VARIADIC after parameter name
• Using non-array type with VARIADIC
• Putting VARIADIC after RETURNS keyword

3. Given the function:

CREATE FUNCTION sum_all(VARIADIC nums int[]) RETURNS int AS $$
  SELECT SUM(n) FROM unnest(nums) AS n;
$$ LANGUAGE sql;

What is the result of SELECT sum_all(2, 4, 6);?

medium

A. ARRAY[2,4,6]

B. 12

C. Error: wrong number of arguments

D. NULL

Solution

1. Step 1: Understand VARIADIC input

   The function accepts any number of integers as separate arguments, packed into an array named nums.

2. Step 2: Calculate the sum

   Input arguments 2, 4, 6 become array [2,4,6]. The function sums these values: 2 + 4 + 6 = 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   Sum of 2,4,6 = 12 [OK]

Hint: VARIADIC packs inputs as array; sum them inside function [OK]

Common Mistakes:

• Expecting an array output instead of sum
• Thinking VARIADIC requires explicit array input
• Assuming function errors on multiple arguments

4. Consider this function definition:

CREATE FUNCTION concat_texts(VARIADIC texts text) RETURNS text AS $$
  SELECT string_agg(t, ',') FROM unnest(texts) AS t;
$$ LANGUAGE sql;

Which error will occur if you call SELECT concat_texts('hello', 'world');?

medium

A. Error: VARIADIC parameter must be declared as an array type

B. No error, returns 'hello,world'

C. Error: missing FROM-clause entry for table 'texts'

D. Error: function does not exist

Solution

1. Step 1: Check VARIADIC parameter type

   The parameter texts is declared as text, not text[]. VARIADIC requires an array type.

2. Step 2: Identify error cause

   PostgreSQL will raise a syntax error because VARIADIC must be followed by an array type, e.g., VARIADIC texts text[].

3. Final Answer:

   Error: VARIADIC parameter must be declared as an array type -> Option A

4. Quick Check:

   VARIADIC needs array type parameter [OK]

Hint: VARIADIC param must be array type, else syntax error [OK]

Common Mistakes:

• Declaring VARIADIC param as scalar type
• Expecting no error with wrong type
• Confusing error with missing FROM clause

5. You want to create a function that accepts a fixed integer and then any number of text arguments variadically. Which of these function declarations is correct?

hard

A. CREATE FUNCTION example(fixed int, VARIADIC texts text) RETURNS text AS $$ ... $$ LANGUAGE sql;

B. CREATE FUNCTION example(VARIADIC texts text[], fixed int) RETURNS text AS $$ ... $$ LANGUAGE sql;

C. CREATE FUNCTION example(fixed int, texts VARIADIC text[]) RETURNS text AS $$ ... $$ LANGUAGE sql;

D. CREATE FUNCTION example(fixed int, VARIADIC texts text[]) RETURNS text AS $$ ... $$ LANGUAGE sql;

Solution

1. Step 1: Recall VARIADIC position rule

   VARIADIC parameter must be the last parameter in the function declaration.

2. Step 2: Check parameter types and order

   CREATE FUNCTION example(fixed int, VARIADIC texts text[]) RETURNS text AS $$ ... $$ LANGUAGE sql; places fixed int first and VARIADIC texts text[] last, which is correct. CREATE FUNCTION example(VARIADIC texts text[], fixed int) RETURNS text AS $$ ... $$ LANGUAGE sql; places VARIADIC first, which is invalid. CREATE FUNCTION example(fixed int, texts VARIADIC text[]) RETURNS text AS $$ ... $$ LANGUAGE sql; misplaces VARIADIC keyword. CREATE FUNCTION example(fixed int, VARIADIC texts text) RETURNS text AS $$ ... $$ LANGUAGE sql; uses non-array type with VARIADIC.

3. Final Answer:

   CREATE FUNCTION example(fixed int, VARIADIC texts text[]) RETURNS text AS $$ ... $$ LANGUAGE sql; -> Option D

4. Quick Check:

   VARIADIC last and array type = correct [OK]

Hint: VARIADIC param must be last and array type [OK]

Common Mistakes:

• Placing VARIADIC parameter before fixed parameters
• Using scalar type with VARIADIC
• Misplacing VARIADIC keyword after parameter name