本文介绍了SQL中常用的字符串操作技巧，包括如何使用substr函数截取字符串，以及如何通过字符串相加实现数据拼接。同时，还提供了包含特殊字符的查询条件处理方法。
1.截取字符串：
substr('This is a test', 6, 2) would return 'is'
substr('This is a test', 6) would return 'is a test'
substr('TechOnTheNet', 1, 4) would return 'Tech'
substr('TechOnTheNet', -3, 3) would return 'Net'
substr('TechOnTheNet', -6, 3) would return 'The'
substr('TechOnTheNet', -8, 2) would return 'On'
2.字符串相加：'aaa '|| 'bbb '
3.select * from a where b='sdfsf''sdfsf'
当搜索条件中有单引号时，两个单引号表示一个单引号
substr('This is a test', 6, 2) would return 'is'
substr('This is a test', 6) would return 'is a test'
substr('TechOnTheNet', 1, 4) would return 'Tech'
substr('TechOnTheNet', -3, 3) would return 'Net'
substr('TechOnTheNet', -6, 3) would return 'The'
substr('TechOnTheNet', -8, 2) would return 'On'
2.字符串相加：'aaa '|| 'bbb '
3.select * from a where b='sdfsf''sdfsf'
当搜索条件中有单引号时，两个单引号表示一个单引号
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