MySQL 查詢使日期列為 NULL？

To make a date column null, use ALTER TABLE and MODIFY and set the date to NULL. Following is the syntax −

alter table yourTableName modify column yourColumnName date NULL;

首先讓我們建立一個表格。在這裡，我們將列設為NOT NULL −

mysql> create table DemoTable
(
   ShippingDate date NOT NULL
);
Query OK, 0 rows affected (0.78 sec)

Now, insert NULL value in the above table. An error would generate since we have set the column to be NOT NULL −

mysql> insert into DemoTable values(null);
ERROR 1048 (23000) − Column 'ShippingDate' cannot be null

Now, let us alter the table and allow NULL in the above table −

mysql> alter table DemoTable modify column ShippingDate date NULL;
Query OK, 0 rows affected (1.81 sec)
Records : 0 Duplicates : 0 Warnings : 0

現在，再次嘗試使用插入命令將NULL插入到上述表中。由於我們已經修改了表以接受NULL，所以不會產生錯誤−

mysql> insert into DemoTable values(null);
Query OK, 1 row affected (1.21 sec

Display all records from the table using select statement −

mysql> select *from DemoTable;

這將產生以下輸出−

+--------------+
| ShippingDate |
+--------------+
| NULL         |
+--------------+
1 row in set (0.00 sec)

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