How Can I Concatenate Values Across Multiple Rows in PostgreSQL?
Jan 21, 2025 am 09:22 AMPostgreSQL data row value connection
In relational database operations, it is often necessary to process the data before obtaining the final result. A common task is to concatenate values from multiple rows based on a common identifier. In PostgreSQL, the GROUP_CONCAT
function provides a simple solution for this.
GROUP_CONCAT
Function
PostgreSQL version 9.0 and above introduced the GROUP_CONCAT
aggregation function, which takes a set of values in a column and concatenates them into a single string. The syntax of GROUP_CONCAT
is as follows:
GROUP_CONCAT(DISTINCT expression [ORDER BY expression] [separator])
Parameters:
- DISTINCT: (optional) Prevents duplicate values from being included in the results.
- expression: The column or expression to join.
- ORDER BY: (optional) Specifies the order in which values are concatenated.
- separator: (optional) Character or string used to separate concatenated values. The default is comma (,).
Example
Consider the following table named "sample_data":
id | value |
---|---|
TM67 | 4 |
TM67 | 9 |
TM67 | 72 |
TM99 | 2 |
TM99 | 3 |
To join the values in the "value" column for each unique "id" we can use GROUP_CONCAT
like this:
SELECT id, GROUP_CONCAT(value) AS concatenated_values FROM sample_data GROUP BY id;
This query will produce the following output:
id | concatenated_values |
---|---|
TM67 | 4,9,72 |
TM99 | 2,3 |
As you can see, the values for each "id" are concatenated and separated by commas.
Alternative syntax for PostgreSQL 9.0
Starting with PostgreSQL version 9.0, an alternative syntax for GROUP_CONCAT
can be used:
SELECT id, string_agg(value, ',') AS concatenated_values FROM sample_data GROUP BY id;
This syntax is equivalent to the GROUP_CONCAT
syntax described above.
Conclusion
You can easily join multiple rows of data in PostgreSQL by using the GROUP_CONCAT
or string_agg
function. Which syntax you choose depends on your PostgreSQL version and personal preference.
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