How to Efficiently Extract Columns from Records Returned by a Database Function?

Columns Concatenated in Record Returned by Function

When joining a table with a function that returns multiple columns, it's essential to account for potential data concatenation issues. To address this challenge, let's explore different approaches for extracting individual columns from the returned record.

General Approach for Decomposing Rows

To decompose the rows returned by a function, use the following syntax:

SELECT * FROM function_name(arguments);

Postgres 9.3 and Newer: Using JOIN LATERAL to Decompose Results

For Postgres 9.3 or above, you can leverage JOIN LATERAL to decompose the results more cleanly:

SELECT ...
FROM table_name a
JOIN LATERAL function_name(a.accountid, '2014-08-12') f
WHERE ...

Postgres 9.2 or Older: Decomposing Results Using a Subquery

In earlier Postgres versions, you can decompose the results using a subquery:

SELECT ...
FROM (
   SELECT a.*, function_name(a.accountid, '2014-08-12') AS rec
   FROM table_name a
   WHERE ...
) a

Best Practices for Decomposing Results

• Decompose the record in the outer query to avoid repeated function evaluations.
• Be cautious of potential duplicate column names when decomposing the record.
• For better performance, use NOT EXISTS instead of NOT IN (subquery) for row filtering.

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