Store select query's output in one array in postgres

Deeper into array storage of query results

Taking this discussion further, PostgreSQL presents additional methods for storing query results as arrays. These are the goodie bag tricks of experienced programmers who know every option matters.

The array constructor method

Sometimes, we don't want the entire row but just one column. Array constructor lets us do that:

SELECT ARRAY(SELECT t.column1 FROM your_table as t);
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This handy command lets us create an array of 'column1' values only. It's like getting the flavor you want in a bag of assorted jelly beans.

Query and fetch column names

Ah! The convenience of automation. How about a query that gets us column names of a table and stores them in an array? Take a look:

SELECT ARRAY_AGG(column_name::text) 
FROM information_schema.columns 
WHERE table_name = 'your_table';
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Save the manual labor. This does everything for you and gift wraps the column names into an array.

Direct storage with SELECT...INTO

The SELECT...INTO syntax allows us to create an array variable containing our results directly, kind of like a quick takeaway meal:

DO $$
DECLARE
  my_array TEXT[];
BEGIN
  SELECT ARRAY_AGG(column1) INTO my_array FROM your_table;
END $$;
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Ensure you do typecasting when necessary while using this method to avoid runtime stomach aches.

Playing with data types in arrays

While working with arrays, consider your schema definition and data types well, especially when dealing with multidimensional arrays or arrays of composite types:

SELECT ARRAY_AGG(ROW(t.column1, t.column2)::your_composite_type) FROM your_table as t;
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This prepares a whole meal of data types for our array. Be sure your typecasts align well with the expected dish.

Advanced use cases and debugging

Buckle up as we explore some advanced practices and debugging techniques for handling the unexpected. You never know when these might save your day.

Catching unexpected output

Debugging is the programming equivalent of a bedtime story's plot twist. Here's how to catch the monster under your code's bed:

BEGIN
  -- your code
EXCEPTION WHEN OTHERS THEN
  RAISE NOTICE 'Exception: %', SQLERRM;
END;
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Manipulating and formatting arrays

format() helps us dress our queries for the ball, while string_agg() converts arrays to a string, like turning pumpkins into carriages:

SELECT string_agg(array_element::text, ', ') FROM UNNEST(your_array) AS array_element;
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Guard your castle with defensive programming

Practising defensive programming is like having a double-checking fairy by your side. Always ensure your table and columns exist before executing your queries:

IF EXISTS(SELECT 1 FROM information_schema.tables WHERE table_name = 'your_table') THEN
  -- your query
END IF;
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Encapsulate logic in functions

We can also encapsulate logic into PL/pgSQL functions for more readable, reusable, and elegant code:

CREATE OR REPLACE FUNCTION aggregate_to_array() RETURNS TEXT[] AS $$
BEGIN
  RETURN ARRAY(SELECT column1 FROM your_table);
END;
$$ LANGUAGE plpgsql;
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