How Can I Concatenate Character(2) Columns in PostgreSQL SELECT Statements?

Combining Character(2) Columns in PostgreSQL Queries

When working with PostgreSQL SELECT statements, combining character(2) columns can present a challenge due to the concatenation operator (||) requiring at least one string input.

One solution is to explicitly cast one of the character(2) columns to the text data type before concatenation. This ensures both inputs are string types, allowing for successful concatenation. For instance:

<code class="language-sql">SELECT a::text || b AS combined_column FROM foo;</code>

Alternatively, the concat_ws() function offers a robust solution. This function handles multiple inputs, concatenating them with a specified separator and gracefully managing NULL values. This prevents NULL results even if one of the input columns contains a NULL value. Example:

<code class="language-sql">SELECT concat_ws(', ', a, b) AS combined_column FROM foo;</code>

For scenarios demanding immutable functions (e.g., for indexes, generated columns, or partitioning), a custom immutable function based on concat_ws() or an alternative strategy, such as adding and updating a new combined column via a database trigger, is recommended.

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