Purpose
This function is used for column-to-row conversion, merging the values of measure columns. It can be used as an aggregate or analysis function.
Note
- When used as an analytic function, you must use the
OVERclause to define a window for calculation. This function divides the query result set into several groups based on one or more expressions in thequery_partition_clause. - When used as an aggregate function, the
OVERkeyword is not required.- As an aggregate function for a single set,
WM_CONCAToperates on all rows and returns a single output row. - As a group aggregation function,
WM_CONCAToperates on each group defined by theGROUP BYclause and returns output rows.
- As an aggregate function for a single set,
Syntax
WM_CONCAT ([DISTINCT] measure_expr) [OVER query_partition_clause]
Parameters
Parameter |
Description |
|---|---|
| DISTINCT | If specifiedDISTINCT, which removes duplicate values from the returned result. This option is optional. |
| measure_expr | It can be any expression. Null values in the measure column will be ignored. |
| OVER | UseOVERThe OVER clause defines the window for computation. For more information, see Analysis functions. |
Return type
Returns a data value of the CLOB type.
Examples
There is already a table named employees.
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
Aggregate functions
Place all the names in column last_name on one line.
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
Examples of analytic functions
Group by the department_id column and query all last_name values within the same 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