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

• delimiter — A string that will be used to separate concatenated values. This parameter is optional and defaults to an empty string or delimiter from parameters if not specified.
• expression — The expression or column name that outputs strings to be concatenated.

Parameters

• 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.

Also, if different delimiters are specified as parameters and arguments, the delimiter from arguments will be used only. :::

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.