How to Replace MySQL's GROUP_CONCAT with PostgreSQL's STRING_AGG?

Migrating from MySQL's GROUP_CONCAT to PostgreSQL's STRING_AGG

MySQL's GROUP_CONCAT function efficiently combines values from multiple rows into a single string. PostgreSQL offers the STRING_AGG function to achieve the same result.

The Solution:

To replicate the functionality of GROUP_CONCAT in your PostgreSQL database, use the STRING_AGG function within your query. For instance, if you want to concatenate values from a column named some_column for each unique id, the query would look like this:

<code class="language-sql">SELECT id, STRING_AGG(some_column, ',')
FROM the_table
GROUP BY id;</code>

Detailed Explanation:

• STRING_AGG(some_column, ','): This part of the query concatenates the values found in the some_column column. The , specifies a comma as the separator between concatenated values. You can change this separator to any other character or string as needed.
• GROUP BY id: This groups the rows based on the id column. The STRING_AGG function then operates on each group separately, concatenating values only within the same id group.

Expected Output:

The query will generate output similar to what you'd get with MySQL's GROUP_CONCAT:

<code>id    | string_agg
------+-----------------
TM67  | 4,9,72
TM99  | 2,3</code>

This demonstrates a direct and effective translation of the MySQL GROUP_CONCAT function's capabilities into a PostgreSQL context using STRING_AGG.

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