How to Reliably Check for a Table's Existence in a Specific PostgreSQL Schema?

Determining Table Existence in a PostgreSQL Schema

PostgreSQL databases often utilize schemas, including the public schema and custom schemas for different organizations. This necessitates reliable methods for confirming the presence of a table within a particular schema.

Limitations of the Information Schema

While the information schema offers a view of database tables, it's restricted to tables accessible by the current user. This limitation can produce false negatives. The following query, using the information schema, might not accurately reflect the table's existence:

<code class="language-sql">SELECT EXISTS (
   SELECT FROM information_schema.tables 
   WHERE  table_schema = 'schema_name'
   AND    table_name   = 'table_name'
   );</code>

Reliable Methods Using System Catalogs

For a more comprehensive check, leverage PostgreSQL's system catalogs. The query below uses pg_class and pg_namespace to reliably determine if a table exists, regardless of user permissions:

<code class="language-sql">SELECT EXISTS (
   SELECT FROM pg_catalog.pg_class c
   JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
   WHERE  n.nspname = 'schema_name'
   AND    c.relname = 'table_name'
   AND    c.relkind = 'r'    -- only tables
   );</code>

This query returns true if the table exists.

Type Casting for Table Existence Verification

Another technique involves casting the table identifier to the regclass type. A successful cast implies the table's existence; failure results in an exception.

<code class="language-sql">SELECT 'schema_name.table_name'::regclass;</code>

Using to_regclass (PostgreSQL 9.4 and later)

For PostgreSQL 9.4 and subsequent versions, the to_regclass function provides a more robust solution. It returns NULL if the table is absent, avoiding exceptions:

<code class="language-sql">SELECT to_regclass('schema_name.table_name');</code>

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