LISTAGG window function - Amazon Redshift

LISTAGG window function

For each group in a query, the LISTAGG window 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.

Syntax

LISTAGG( [DISTINCT] expression [, 'delimiter' ] ) [ WITHIN GROUP (ORDER BY order_list) ] OVER ( [PARTITION BY partition_expression] )

Arguments

DISTINCT

(Optional) A clause that eliminates duplicate values from the specified expression before concatenating. Trailing spaces are ignored, so 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

(Optional) The string constant to will separate the concatenated values. The default is NULL.

WITHIN GROUP (ORDER BY order_list)

(Optional) A clause that specifies the sort order of the aggregated values. Deterministic only if ORDER BY provides unique ordering. The default is to aggregate all rows and return a single value.

OVER

A clause that specifies the window partitioning. The OVER clause cannot contain a window ordering or window frame specification.

PARTITION BY partition_expression

(Optional) Sets the range of records for each group in the OVER clause.

Returns

VARCHAR(MAX). If the result set is larger than the maximum VARCHAR size (64K – 1, or 65535), then LISTAGG returns the following error:

Invalid operation: Result size exceeds LISTAGG limit

Examples

The following examples uses the WINSALES table. For a description of the WINSALES table, see Overview example for window functions.

The following example returns a list of seller IDs, ordered by seller ID.

select listagg(sellerid) within group (order by sellerid) over() from winsales; listagg ------------ 11122333344 ... ... 11122333344 11122333344   (11 rows)

The following example returns a list of seller IDs for buyer B, ordered by date.

select listagg(sellerid) within group (order by dateid) over () as seller from winsales where buyerid = 'b' ; seller --------- 3233 3233 3233 3233 (4 rows)

The following example returns a comma-separated list of sales dates for buyer B.

select listagg(dateid,',') within group (order by sellerid desc,salesid asc) over () as dates from winsales where buyerid = 'b'; dates ------------------------------------------- 2003-08-02,2004-04-18,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-04-18,2004-02-12 (4 rows)

The following example uses DISTINCT to return a list of unique sales dates for buyer B.

select listagg(distinct dateid,',') within group (order by sellerid desc,salesid asc) over () as dates from winsales where buyerid = 'b'; dates -------------------------------- 2003-08-02,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-02-12 2003-08-02,2004-04-18,2004-02-12 (4 rows)

The following example returns a comma-separated list of sales IDs for each buyer ID.

select buyerid, listagg(salesid,',') within group (order by salesid) over (partition by buyerid) as sales_id from winsales order by buyerid; buyerid | sales_id -----------+------------------------ a |10005,40001,40005 a |10005,40001,40005 a |10005,40001,40005 b |20001,30001,30004,30003 b |20001,30001,30004,30003 b |20001,30001,30004,30003 b |20001,30001,30004,30003 c |10001,20002,30007,10006 c |10001,20002,30007,10006 c |10001,20002,30007,10006 c |10001,20002,30007,10006 (11 rows)