PostgreSQL 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 ​​of multiple rows based on common identifiers. In PostgreSQL, the GROUP_CONCAT function provides a simple solution for this.

GROUP_CONCAT Function

PostgreSQL version 9.0 and above introduces the GROUP_CONCAT aggregate function, which takes a set of values ​​in a column and concatenates them into a single string. GROUP_CONCAT syntax is as follows:

GROUP_CONCAT(DISTINCT expression [ORDER BY expression] [separator])

parameter:

• DISTINCT: (optional) Prevent duplicate values ​​from being included in the result.
• expression: The column or expression to be joined.
• ORDER BY: (optional) Specifies the order of joining values.
• separator: (optional) A character or string used to separate the concatenated values. Default is comma (,).

Example

Consider the following table called "sample_data":

SELECT id, GROUP_CONCAT(value) AS concatenated_values
FROM sample_data
GROUP BY id;

SELECT id, GROUP_CONCAT(value) AS concatenated_values FROM sample_data GROUP BY id;

]

] As you can see, the values ​​of each "id" are concatenated and separated by commas.

SELECT id, string_agg(value, ',') AS concatenated_values
FROM sample_data
GROUP BY id;

SELECT id, string_agg(value, ',') AS concatenated_values FROM sample_data GROUP BY id;

GROUP_CONCAT syntax described above. in conclusion

GROUP_CONCAT or the

functions, you can easily concatenate multi-row data in PostgreSQL. Which syntax to choose depends on your PostgreSQL version and personal preferences.