INSERT INTO與SELECT

Question

我試圖插入表格從結果從表B中收集空的結果：

INSERT INTO A (x, y, created_at) 
(SELECT x, "something", a_timestamp 
FROM B WHERE c IS NULL AND a_timestamp > NOW()) 

的問題是，對於某些情況下

(SELECT x, "something", a_timestamp 
FROM B WHERE c IS NULL AND a_timestamp > NOW()) 

沒有按不會返回任何記錄（這是可以的），但是另一個INSERT失敗。

我該如何掩蓋自己的情況？

謝謝！

Answer 1

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

要

"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" 

Answer 2

我無法重現錯誤：

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) 

見db-fiddle。