GENERATOR
Declaration
GENERATOR(N)
Description
This function is an inbuilt function in the Table Function framework. It allows you to call it in a Table Function and returns N rows of data. N is a 64-bit unsigned integer greater than or equal to 0.
A table function is a function used in SQL that returns a data table as a result. Unlike traditional SQL functions that return scalar values, table functions can return datasets with multiple rows and columns.
TABLE(GENERATOR(N)) does not generate any data. It only generates N consecutive rows. If you need to generate data, you must add specific expressions, such as constants, variables, functions, or UDFs, after SELECT. TABLE(GENERATOR(N)) can be used in parallel operations, such as parallel SELECT and parallel DML. However, only one thread is responsible for reading the rows generated by TABLE(GENERATOR(N)), which means that the DFO containing TABLE(GENERATOR(N)) has a DOP=1.
Examples
The following example shows how to use the GENERATOR() function to generate random numbers that meet the specified conditions.
SELECT COUNT(*) FROM TABLE(GENERATOR(100000));
+----------+
| COUNT(*) |
+----------+
| 100000 |
+----------+
1 row in set (0.001 sec)
SELECT NORMAL(0, 1, RANDOM()) FROM TABLE(GENERATOR(5));
+------------------------+
| NORMAL(0, 1, RANDOM()) |
|------------------------|
| 0.227384164 |
| 0.9945290748 |
| -0.2045078571 |
| -1.594607893 |
| -0.8213296842 |
+------------------------+
5 rows in set (0.001 sec)
SELECT RANDSTR(1, ZIPF(1, 5, RANDOM())) str FROM TABLE(GENERATOR(5));
+------------------------+
| str |
|------------------------|
| A |
| D |
| A |
| A |
| C |
+------------------------+
5 rows in set (0.001 sec)
The GENERATOR() function can also be joined with other tables. Here is an example:
CREATE TABLE t1 (c1 BIGINT);
Query OK, 0 rows affected (0.140 sec)
INSERT INTO t1 VALUES (1), (2);
Query OK, 2 rows affected (0.002 sec)
Records: 2 Duplicates: 0 Warnings: 0
SELECT c1, RANDOM(1) FROM t1, TABLE(GENERATOR(3));
+------+----------------------+
| c1 | random(1) |
+------+----------------------+
| 1 | -6753783847308464280 |
| 2 | -6707106347154343346 |
| 1 | -899926183391115878 |
| 2 | -8835543475904200562 |
| 1 | -2750444335953844424 |
| 2 | 7588216632478230601 |
+------+----------------------+
6 rows in set (0.002 sec)
EXPLAIN SELECT c1, RANDOM(1) FROM t1, TABLE(GENERATOR(3));
+------------------------------------------------------------------------+
| Query Plan |
+------------------------------------------------------------------------+
| ================================================================== |
| |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| |
| ------------------------------------------------------------------ |
| |0 |NESTED-LOOP JOIN CARTESIAN | |398 |14 | |
| |1 |├─FUNCTION_TABLE |FUNC_TABLE1|199 |1 | |
| |2 |└─MATERIAL | |2 |2 | |
| |3 | └─TABLE FULL SCAN |t1 |2 |2 | |
| ================================================================== |
| Outputs & filters: |
| ------------------------------------- |
| 0 - output([t1.c1], [RANDOM(1)]), filter(nil), rowset=256 |
| conds(nil), nl_params_(nil), use_batch=false |
| 1 - output(nil), filter(nil) |
| value(GENERATOR(3)) |
| 2 - output([t1.c1]), filter(nil), rowset=256 |
| 3 - output([t1.c1]), filter(nil), rowset=256 |
| access([t1.c1]), partitions(p0) |
| is_index_back=false, is_global_index=false, |
| range_key([t1.__pk_increment]), range(MIN ; MAX)always true |
+------------------------------------------------------------------------+
19 rows in set (0.001 sec)
SELECT /*+ PARALLEL(2) */ c1, RANDOM(1) FROM t1, TABLE(GENERATOR(3));
+------+----------------------+
| c1 | random(1) |
+------+----------------------+
| 1 | -6753783847308464280 |
| 2 | -6707106347154343346 |
| 1 | -899926183391115878 |
| 2 | -8835543475904200562 |
| 1 | -2750444335953844424 |
| 2 | 7588216632478230601 |
+------+----------------------+
6 rows in set (0.001 sec)
EXPLAIN SELECT /*+ PARALLEL(2) */ c1, RANDOM(1) FROM t1, TABLE(GENERATOR(3));
+------------------------------------------------------------------------+
| Query Plan |
+------------------------------------------------------------------------+
| ================================================================== |
| |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| |
| ------------------------------------------------------------------ |
| |0 |NESTED-LOOP JOIN CARTESIAN | |398 |13 | |
| |1 |├─FUNCTION_TABLE |FUNC_TABLE1|199 |1 | |
| |2 |└─MATERIAL | |2 |2 | |
| |3 | └─PX COORDINATOR | |2 |2 | |
| |4 | └─EXCHANGE OUT DISTR |:EX10000 |2 |2 | |
| |5 | └─PX BLOCK ITERATOR | |2 |1 | |
| |6 | └─TABLE FULL SCAN |t1 |2 |1 | |
| ================================================================== |
| Outputs & filters: |
| ------------------------------------- |
| 0 - output([t1.c1], [RANDOM(1)]), filter(nil), rowset=256 |
| conds(nil), nl_params_(nil), use_batch=false |
| 1 - output(nil), filter(nil) |
| value(GENERATOR(3)) |
| 2 - output([t1.c1]), filter(nil), rowset=256 |
| 3 - output([t1.c1]), filter(nil), rowset=256 |
| 4 - output([t1.c1]), filter(nil), rowset=256 |
| dop=2 |
| 5 - output([t1.c1]), filter(nil), rowset=256 |
| 6 - output([t1.c1]), filter(nil), rowset=256 |
| access([t1.c1]), partitions(p0) |
| is_index_back=false, is_global_index=false, |
| range_key([t1.__pk_increment]), range(MIN ; MAX)always true |
+------------------------------------------------------------------------+
26 rows in set (0.002 sec)