如何限制 MySQL SELECT 结果中 longtext 字段的长度？

可以使用 MySQL 中的 SUBSTRING() 来限制字符串的长度。语法如下

SELECT SUBSTRING(yourColumnName,1,yourIntegerValueToGetTheCharacters) 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 limitLengthOfLongTextDemo
   -> (
   -> sentence LONGTEXT
   -> );
Query OK, 0 rows affected (0.74 sec)

使用插入命令插入一些记录到表中。查询如下

mysql> insert into limitLengthOfLongTextDemo values('This is the introduction to MySQL');
Query OK, 1 row affected (0.17 sec)

mysql> insert into limitLengthOfLongTextDemo values('PL/SQL is the extension of Structured
Query Language');
Query OK, 1 row affected (0.19 sec)

mysql> insert into limitLengthOfLongTextDemo values('Java is an Object Oriented
Programming Language');
Query OK, 1 row affected (0.20 sec)

使用 select 语句显示表中的所有记录。查询如下

mysql> select *from limitLengthOfLongTextDemo;

以下是输出

+------------------------------------------------------+
| sentence                                             |
+------------------------------------------------------+
| This is the introduction to MySQL                    |
| PL/SQL is the extension of Structured Query Language |
| Java is an Object Oriented Programming Language      |
+------------------------------------------------------+
3 rows in set (0.00 sec)

以下是获取给定值字符的查询

mysql> select substring(sentence,1,26) as 26Characters from limitLengthOfLongTextDemo;

以下是输出

+----------------------------+
| 26Characters               |
+----------------------------+
| This is the introduction t |
| PL/SQL is the extension of |
| Java is an Object Oriented |
+----------------------------+
3 rows in set (0.00 sec)

更新于： 30-Jul-2019

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