INSERT INTO with empty results from SELECT - mysql

Question

I'm trying to insert into table A from the results gather from table B:
INSERT INTO A (x, y, created_at)
(SELECT x, "something", a_timestamp
FROM B WHERE c IS NULL AND a_timestamp > NOW())
The issue is that, for some instances
(SELECT x, "something", a_timestamp
FROM B WHERE c IS NULL AND a_timestamp > NOW())
doesn't return any records (which is okay), but then the other INSERT fails.
How can I cover myself from that scenario?
Thanks!

Answer 1

I can't reproduce the error:
mysql> DROP TABLE IF EXISTS `tbl_test`;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> CREATE TABLE IF NOT EXISTS `tbl_test` (
-> `id` TINYINT
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO `tbl_test`
-> SELECT 1
-> FROM DUAL
-> WHERE 0 = 0;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> SELECT `id` FROM `tbl_test`;
+------+
| id |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
mysql> INSERT INTO `tbl_test`
-> SELECT 1
-> FROM DUAL
-> WHERE 0 = 1;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> SELECT `id` FROM `tbl_test`;
+------+
| id |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
UPDATE
mysql> DROP TABLE IF EXISTS `tbl_test`;
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE IF NOT EXISTS `tbl_test` (
-> `id` TINYINT
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO `tbl_test`
-> (`id`)
-> VALUES
-> (101);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT `id`
-> FROM `tbl_test`;
+------+
| id |
+------+
| 101 |
+------+
1 row in set (0.00 sec)
mysql> INSERT INTO `tbl_test`
-> SELECT `id` + 1
-> FROM `tbl_test`
-> WHERE `id` > 100;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> SELECT `id`
-> FROM `tbl_test`;
+------+
| id |
+------+
| 101 |
| 102 |
+------+
2 rows in set (0.00 sec)
mysql> INSERT INTO `tbl_test`
-> SELECT `id` + 1
-> FROM `tbl_test`
-> WHERE `id` < 100;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> SELECT `id`
-> FROM `tbl_test`;
+------+
| id |
+------+
| 101 |
| 102 |
+------+
2 rows in set (0.00 sec)
See db-fiddle.

Answer 2

You can use INSERT IGNORE INTO to address your issue.
For example:
INSERT IGNORE INTO A (x, y, created_at)
(SELECT x, "something", a_timestamp
FROM B WHERE c IS NULL AND a_timestamp > NOW())
More info can be found here

Answer 3

"INSERT INTO A (x, y, created_at)
(SELECT x, \"something\", a_timestamp
FROM B WHERE c IS NULL AND a_timestamp > \"#{current_time}\")
To
"INSERT INTO A (x, y, created_at)
(SELECT x, \"something\", a_timestamp
FROM B WHERE c IS NULL AND a_timestamp > \"#{current_time}\")
AND (SELECT count(x) FROM B WHERE c IS NULL AND a_timestamp > \"#{current_time}\")) > 0"