ClickHouse/docs/en/sql-reference/aggregate-functions/reference/groupconcat.md

slug	sidebar_position	sidebar_label	title
/en/sql-reference/aggregate-functions/reference/groupconcat	363	groupConcat	groupConcat

Calculates a concatenated string from a group of strings, optionally separated by a delimiter, and optionally limited by a maximum number of elements.

Syntax

groupConcat[(delimiter [, limit])](expression);

Arguments

• expression — The expression or column name that outputs strings to be concatenated..
• delimiter — A string that will be used to separate concatenated values. This parameter is optional and defaults to an empty string if not specified.
• limit — A positive integer specifying the maximum number of elements to concatenate. If more elements are present, excess elements are ignored. This parameter is optional.

:::note If delimiter is specified without limit, it must be the first parameter. If both delimiter and limit are specified, delimiter must precede limit. :::

Returned value

• Returns a string consisting of the concatenated values of the column or expression. If the group has no elements or only null elements, and the function does not specify a handling for only null values, the result is a nullable string with a null value.

Examples

Input table:

┌─id─┬─name─┐
│  1 │ John │
│  2 │ Jane │
│  3 │ Bob  │
└────┴──────┘

1. Basic usage without a delimiter:

Query:

SELECT groupConcat(Name) FROM Employees;

Result:

JohnJaneBob

This concatenates all names into one continuous string without any separator.

2. Using comma as a delimiter:

Query:

SELECT groupConcat(', ')(Name)  FROM Employees;

Result:

John, Jane, Bob

This output shows the names separated by a comma followed by a space.

3. Limiting the number of concatenated elements

Query:

SELECT groupConcat(', ', 2)(Name) FROM Employees;

Result:

John, Jane

This query limits the output to the first two names, even though there are more names in the table.