在MySQL中从天，月，年字段创建日期？

您可以使用MySQL中内置的函数STR_TO_DATE()。语法如下 –

SELECT
STR_TO_DATE(CONCAT(yourYearColumName,'-',LPAD(yourMonthColumName,2,'00'),'-',LPAD(yourDayColumName,2,'00')), '%Y-%m-%d') as anyVariableName from yourTableName;

为了理解上面的语法，让我们创建一个表。创建表的查询语句如下 –

mysql> create table DateCreateDemo
   −> (
   −> `Day` varchar(2),
   −> `Month` varchar(2),
   −> `Year` varchar(4)
   −> );
Query OK, 0 rows affected (1.68 sec)

使用insert命令为所有字段插入值。查询语句如下 –

mysql > insert into DateCreateDemo values('15','12','2018');
Query OK, 1 row affected (0.09 sec)

mysql > insert into DateCreateDemo values('10','11','2016');
Query OK, 1 row affected (0.37 sec)

mysql > insert into DateCreateDemo values('12','6','2017');
Query OK, 1 row affected (0.12 sec)

mysql > insert into DateCreateDemo values('9','8','2019');
Query OK, 1 row affected (0.17 sec)

mysql > insert into DateCreateDemo values('10','5','2020');
Query OK, 1 row affected (0.09 sec)

使用select语句显示表中的所有记录。查询语句如下 –

mysql > select *from DateCreateDemo;

以下是输出 –

+------+-------+------+
| Day  | Month | Year |
+------+-------+------+
| 15   | 12    | 2018 |
| 10   | 11    | 2016 |
| 12   | 6     | 2017 |
| 9    | 8     | 2019 |
| 10   | 5     | 2020 |
+------+-------+------+
5 rows in set (0.00 sec)

使用上面的三个字段（’Day’，’Month’和’Year’）创建一个日期。查询语句如下 –

mysql > select
   −> STR_TO_DATE(CONCAT(Year,'-',LPAD(Month,2,'00'),'-',LPAD(day,2,'00')), '%Y-%m-%d') as DateDemo from DateCreateDemo;

以下是输出结果 –

+------------+
| DateDemo   |
+------------+
| 2018-12-15 |
| 2016-11-10 |
| 2017-06-12 |
| 2019-08-09 |
| 2020-05-10 |
+------------+
5 rows in set (0.06 sec)