LISTAGG function - Amazon Redshift

LISTAGG function

For each group in a query, the LISTAGG aggregate function orders the rows for that group according to the ORDER BY expression, then concatenates the values into a single string.

LISTAGG is a compute node-only function. The function returns an error if the query doesn't reference a user-defined table or Amazon Redshift system table. For more information, see Querying the catalog tables.

Syntax

LISTAGG( [DISTINCT] aggregate_expression [, 'delimiter' ] ) [ WITHIN GROUP (ORDER BY order_list) ]

Arguments

DISTINCT

A clause that eliminates duplicate values from the specified expression before concatenating. Trailing spaces are ignored. For example, the strings 'a' and 'a ' are treated as duplicates. LISTAGG uses the first value encountered. For more information, see Significance of trailing blanks.

aggregate_expression

Any valid expression, such as a column name, that provides the values to aggregate. NULL values and empty strings are ignored.

delimiter

The string constant to separate the concatenated values. The default is NULL.

WITHIN GROUP (ORDER BY order_list)

A clause that specifies the sort order of the aggregated values.

Returns

VARCHAR(MAX). If the result set is larger than the maximum VARCHAR size, LISTAGG returns the following error:

Invalid operation: Result size exceeds LISTAGG limit

Usage notes

  • If a statement includes multiple LISTAGG functions that use WITHIN GROUP clauses, each WITHIN GROUP clause must use the same ORDER BY values.

    For example, the following statement returns an error.

    SELECT LISTAGG(sellerid) WITHIN GROUP (ORDER BY dateid) AS sellers, LISTAGG(dateid) WITHIN GROUP (ORDER BY sellerid) AS dates FROM sales;

    The following statements runs successfully.

    SELECT LISTAGG(sellerid) WITHIN GROUP (ORDER BY dateid) AS sellers, LISTAGG(dateid) WITHIN GROUP (ORDER BY dateid) AS dates FROM sales; SELECT LISTAGG(sellerid) WITHIN GROUP (ORDER BY dateid) AS sellers, LISTAGG(dateid) AS dates FROM sales;

Examples

The following example aggregates seller IDs, ordered by seller ID.

SELECT LISTAGG(sellerid, ', ') WITHIN GROUP (ORDER BY sellerid) FROM sales WHERE eventid = 4337; listagg ---------------------------------------------------------------------------------------------------------------------------------------- 380, 380, 1178, 1178, 1178, 2731, 8117, 12905, 32043, 32043, 32043, 32432, 32432, 38669, 38750, 41498, 45676, 46324, 47188, 47188, 48294

The following example uses DISTINCT to return a list of unique seller IDs.

SELECT LISTAGG(DISTINCT sellerid, ', ') WITHIN GROUP (ORDER BY sellerid) FROM sales WHERE eventid = 4337; listagg ------------------------------------------------------------------------------------------- 380, 1178, 2731, 8117, 12905, 32043, 32432, 38669, 38750, 41498, 45676, 46324, 47188, 48294

The following example aggregates seller IDs in date order.

SELECT LISTAGG(sellerid, ', ') WITHIN GROUP (ORDER BY dateid) FROM sales WHERE eventid = 4337; listagg ----------------------------------------------------------------------------------------------------------------------------------------- 41498, 47188, 47188, 1178, 1178, 1178, 380, 45676, 46324, 48294, 32043, 32043, 32432, 12905, 8117, 38750, 2731, 32432, 32043, 380, 38669

The following example returns a pipe-separated list of sales dates for the buyer with an ID of 660.

SELECT LISTAGG( (SELECT caldate FROM date WHERE date.dateid=sales.dateid), ' | ' ) WITHIN GROUP (ORDER BY sellerid DESC, salesid ASC) FROM sales WHERE buyerid = 660; listagg ------------------------------------------------- 2008-07-16 | 2008-07-09 | 2008-01-01 | 2008-10-26

The following example returns a comma-separated list of sales IDs for the buyer IDs 660, 661, and 662.

SELECT buyerid, LISTAGG(salesid,', ') WITHIN GROUP (ORDER BY salesid) AS sales_id FROM sales WHERE buyerid BETWEEN 660 AND 662 GROUP BY buyerid ORDER BY buyerid; buyerid | sales_id --------+----------------------------------------------------- 660 | 32872, 33095, 33514, 34548 661 | 19951, 20517, 21695, 21931 662 | 3318, 3823, 4215, 51980, 53202, 55908, 57832, 171603