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From: Marcelo Fernandes <marcefern7@gmail.com>
Date: Mon, 24 Mar 2025 16:42:19 +1300
Message-ID: <CAM2F1VMbOEubpXk44B5KaWKX0OSVrA8-9xqidhJMNtDprhTSTg@mail.gmail.com>
Subject: Best way to check if a table is empty
To: pgsql-general@lists.postgresql.org
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Hi folks,

I came up with three strategies to verify whether a table is empty.

I wanted to sound the community to check whether my assumptions are correct for
each of these strategies, and to also discuss which strategy is best.

## Strategy 1 [possibly best?]

SELECT EXISTS (SELECT 1 FROM foo LIMIT 1);

Pros:
  1. Works with any table.
  2. Relatively fast (if the table is well organised).

Cons:
  1. Sequential Scan
  2. If the table is bloated, it reads more buffers.

## Strategy 2

SELECT min(id) FROM foo;

Pros:
  1. Does an index-only scan on a field that presumably has a PK index.
  2. Works well even if the table is bloated.

Cons:
  1. Sequential Scan if the table does not have a PK index.
  2. Reads a few more buffers than Strategy 1 when the table is well organised.
  3. Performs worse if the index is bloated.

## Strategy 3 [worst]

SELECT count(*) FROM foo;

Pros:
  1. Uses a widespread and intuitive operation (count)

Cons:
  1. Very slow on large tables as it performs a Sequential Scan.


How does all of that sound? Are there further strategies I should consider?
Anything I have missed in the Strategies above?

Regards,
Marcelo.