如何在 MySQL 中选取混合字符串/整数列的最大值?
mysqlmysqli database
要选取混合字符串/整数列的最大值，您需要使用 substring() 函数。语法如下:
SELECT MAX(CAST(SUBSTRING(yourColumnName, 4, length(yourColumnName)-3) AS UNSIGNED)) AS anyVariableName FROM yourTableName;
为了理解上述语法，让我们创建一个表。创建表的查询如下:
mysql> create table StringIntMixHighestDemo -> ( -> InvoiceId int NOT NULL AUTO_INCREMENT, -> InvoiceNumber varchar(20), -> PRIMARY KEY(InvoiceId) -> ); Query OK, 0 rows affected (0.65 sec)
现在您可以使用 insert 命令在表中插入一些记录。查询如下:
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV129');
Query OK, 1 row affected (0.11 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV122');
Query OK, 1 row affected (0.22 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV1');
Query OK, 1 row affected (0.15 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV145');
Query OK, 1 row affected (0.18 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV19');
Query OK, 1 row affected (0.10 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV134');
Query OK, 1 row affected (0.13 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV135');
Query OK, 1 row affected (0.16 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV10');
Query OK, 1 row affected (0.14 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV100');
Query OK, 1 row affected (0.11 sec)
mysql> insert into StringIntMixHighestDemo(InvoiceNumber) values('INV121');
Query OK, 1 row affected (0.27 sec)
使用 select 语句显示表中的所有记录。查询如下:
mysql> select *from StringIntMixHighestDemo;
输出结果如下:
+-----------+---------------+ | InvoiceId | InvoiceNumber | +-----------+---------------+ | 1 | INV129 | | 2 | INV122 | | 3 | INV1 | | 4 | INV145 | | 5 | INV19 | | 6 | INV134 | | 7 | INV135 | | 8 | INV10 | | 9 | INV100 | | 10 | INV121 | +-----------+---------------+ 10 rows in set (0.00 sec)
这是获取字符串/整数列中最大值的查询。查询如下:
mysql> SELECT MAX(CAST(SUBSTRING(InvoiceNumber, 4, length(InvoiceNumber)-3) AS UNSIGNED)) as HighestValue -> from StringIntMixHighestDemo;
输出结果如下:
+--------------+ | HighestValue | +--------------+ | 145 | +--------------+ 1 row in set (0.00 sec)
