The extra single quotes are escape characters.

“额外” 的那个单引号是换码符。

Note that we have used single quotes around the conditional values in the examples.

我们在上面那个举例中对条件值使用了单引号.

For each screen that accepts alphanumeric data entry, try entering text that contains one or more single quotes.

测试屏幕上每一个被说明为必须输入的字段以保证它强制要求你在字段中输入数据。

Since we just want to compare the select parameter against a constant, we wrap the constant in single quotes ('').

既然我们要通过一个常量比较 select 参数，可用单引号 ('') 包含常量。