SEQUENCE_TABLE(n) function¶
Percona Server for MySQL supports the SEQUENCE_TABLE() function.
A sequence of numbers can be defined as an arithmetic progression when the common difference between two consecutive terms is always the same.
The function is an inline table-valued function. A single SELECT statement generates a multi-row result set. In contrast, a scalar function (like EXP(x) or LOWER(str) always returns a single value of a specific data type.
The JSON_TABLE() is the only table function available in Oracle MySQL Server. JSON_TABLE and SEQUENCE_TABLE() are the only table functions available in Percona Server.
The basic syntax is the following:
- SEQUENCE_TABLE(n) [AS] alias
Usage¶
Expected output
SELECT … FROM SEQUENCE_TABLE(n) [AS] alias
SEQUENCE_TABLE(n>) [AS] alias
n: The number of generated values.
As with any derived tables, a table function requires an alias in the SELECT statement.
The result set is a single column with the predefined column name value of type BIGINT UNSIGNED. You can reference the value column in SELECT statements.
The following statements are valid:
mysql> SELECT * FROM SEQUENCE_TABLE(n) AS tt;
mysql> SELECT <expr(value)> FROM SEQUENCE_TABLE(n) AS tt;
The first number in the series, the initial term, is defined as 0 and the series ends with a value less than n. In this example, enter the following statement to generate a sequence:
mysql> SELECT * FROM SEQUENCE_TABLE(3) AS tt;
Expected output
+-------+
| value |
+-------+
| 0 |
| 1 |
| 2 |
+-------+
You can define the initial term using the WHERE clause. The following example starts the sequence with 4.
SELECT value AS result FROM SEQUENCE_TABLE(8) AS tt WHERE value >= 4;
Expected output
+--------+
| result |
+--------+
| 4 |
| 5 |
| 6 |
| 7 |
+--------+
Consecutive terms increase or decrease by a common difference. The default common difference value is 1. However, it is possible to filter the results using the WHERE clause to simulate common differences greater than 1.
The following example prints only even numbers from the 0..7 range:
SELECT value AS result FROM SEQUENCE_TABLE(8) AS tt WHERE value % 2 = 0;
Expected output
+--------+
| result |
+--------+
| 0 |
| 2 |
| 4 |
| 6 |
+--------+
The following is an example of using the function to populate a table with a set of random numbers:
mysql> SELECT FLOOR(RAND() * 100) AS result FROM SEQUENCE_TABLE(4) AS tt;
The output could be the following:
Expected output
+--------+
| result |
+--------+
| 24 |
| 56 |
| 70 |
| 25 |
+--------+
You can populate a table with a set of pseudo-random strings with the following statement:
mysql> SELECT MD5(value) AS result FROM SEQUENCE_TABLE(4) AS tt;
Expected output
+----------------------------------+
| result |
+----------------------------------+
| f17d9c990f40f8ac215f2ecdfd7d0451 |
| 2e5751b7cfd7f053cd29e946fb2649a4 |
| b026324c6904b2a9cb4b88d6d61c81d1 |
| 26ab0db90d72e28ad0ba1e22ee510510 |
+----------------------------------+
You can add the sequence as a column to a new table or an existing table, as shown in this example:
mysql> CREATE TABLE t1 AS SELECT * FROM SEQUENCE_TABLE(4) AS tt;
mysql> SELECT * FROM t1;
Expected output
+-------+
| value |
+-------+
| 0 |
| 1 |
| 2 |
| 3 |
+-------+
There are many uses for a sequence when populating tables.
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