You can also use string functions to report string attributes such as length or position of a sub-string, for example
还可以使用 string 函数来报告字符串属性，如子串的长度或位置，例如
2
As previously mentioned, the contains function implements sub-string matching and therefore returns the value true for the above query.
如前所述，contains函数实现子字符串匹配，因此对于以上查询返回true。
3
Using a text index makes document search much more efficient, as the text data does not need to be examined at query time like it is done with sub-string matching.