Purpose
WMSYS.WM_CONCAT/WM_CONCAT() aggregates data from a number of measure columns into a single row. You can use this function as an aggregate or analytic function.
Note
- When you use this function as an analytic function, use the
OVERclause to define a window over the data on which the function operates. This function divides the query result set into groups based on one or more expressions inquery_partition_clause. - When you use it as an aggregate function, you do not need to add the
OVERkeyword.- As a single-set aggregate function, the
WM_CONCATfunction operates on all rows and returns a single output row. - As a group-set aggregate function, the
WM_CONCATfunction operates on each group specified in theGROUP BYclause and returns an output row.
- As a single-set aggregate function, the
Syntax
WM_CONCAT ([DISTINCT] measure_expr) [OVER query_partition_clause]
Parameters
| Parameter | Description |
|---|---|
| DISTINCT | If you specify the DISTINCT operator, duplicates are eliminated from the result set. This parameter is optional. |
| measure_expr | An expression of any type. NULLs in the measure column are ignored. |
| OVER | You can use the OVER clause to define a window over the data on which the function operates. For more information, see Analytic functions. |
Return type
This function returns data values of the CLOB data type.
Examples
The table employees has been created.
obclient> SELECT * FROM employees;
+---------------+-----------+------------+--------+
| DEPARTMENT_ID | LAST_NAME | HIREDATE | SALARY |
+---------------+-----------+------------+--------+
| 30 | Raphaely | 2017-07-01 | 1700 |
| 30 | De Haan | 2018-05-01 | 11000 |
| 40 | Errazuriz | 2017-07-21 | 1400 |
| 50 | Hartstein | 2019-10-05 | 14000 |
| 50 | Raphaely | 2017-07-22 | 1700 |
| 50 | Weiss | 2019-10-05 | 13500 |
| 90 | Russell | 2019-07-11 | 13000 |
| 90 | Partners | 2018-12-01 | 14000 |
+---------------+-----------+------------+--------+
8 rows in set
Example of an aggregate function
Aggregate all names in the last_name column into a single row.
obclient> SELECT WM_CONCAT(last_name) "Emp_list" FROM employees;
+----------------------------------------------------------------------+
| Emp_list |
+----------------------------------------------------------------------+
| Raphaely,De Haan,Errazuriz,Hartstein,Raphaely,Weiss,Russell,Partners |
+----------------------------------------------------------------------+
1 row in set
Example of an analytic function
Group the data records in the table by the department_id column. Return all last_name in the group.
obclient> SELECT department_id,hiredate,last_name,
WM_CONCAT(last_name) OVER (PARTITION BY department_id) as "Emp_list"
FROM employees
ORDER BY 1,2;
+---------------+------------+-----------+--------------------------+
| DEPARTMENT_ID | HIREDATE | LAST_NAME | Emp_list |
+---------------+------------+-----------+--------------------------+
| 30 | 2017-07-01 | Raphaely | Raphaely,De Haan |
| 30 | 2018-05-01 | De Haan | Raphaely,De Haan |
| 40 | 2017-07-21 | Errazuriz | Errazuriz |
| 50 | 2017-07-22 | Raphaely | Hartstein,Raphaely,Weiss |
| 50 | 2019-10-05 | Hartstein | Hartstein,Raphaely,Weiss |
| 50 | 2019-10-05 | Weiss | Hartstein,Raphaely,Weiss |
| 90 | 2018-12-01 | Partners | Russell,Partners |
| 90 | 2019-07-11 | Russell | Russell,Partners |
+---------------+------------+-----------+--------------------------+
8 rows in set
