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法学研究如何在 MySQL 中选择混合字符串/整数字段的最大值？
要选择混合字符串/整数字段的最大值，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，我们创建一个表格。创建表格的查询如下
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 命令在表格中插入一些记录。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 语句从表格中显示所有记录。查询如下
mysql> select *from StringIntMixHighestDemo;
以下是输出
+-----------+---------------+ | 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)
以下是获取字符串/整数字段中最大值的查询。查询如下
mysql> SELECT MAX(CAST(SUBSTRING(InvoiceNumber, 4, length(InvoiceNumber)-3) AS UNSIGNED)) as HighestValue -> from StringIntMixHighestDemo;
以下是输出
+--------------+ | HighestValue | +--------------+ | 145 | +--------------+ 1 row in set (0.00 sec)
更新于：2019-7-30
248 次浏览
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