我工作的一个数据库sqllite在一个Android应用程序 我想用一个像子句检索SM数据 例如：

I am working on a database with sqllite in an android app I want to retrieve sm data using a like clause ex:

Cursor c = myDB.query(MY_DATABASE_TABLE, null, " SongName LIKE '%"+"=?"+"%'" , 
           new String[]{match_str}, null, null,"SongHit  DESC");

这应该给所有SongName开始match_str，但它不是working.Why？

It should give all SongName starting with match_str but its not working.Why?

推荐答案

本：

" SongName LIKE '%"+"=?"+"%'"

最终会这样看，当SQL跨preTER看到它：

Will end up looking like this when the SQL interpreter sees it:

" SongName LIKE '%=?%'"

这将匹配包含文字的任何SongName=？我不认为这就像你想要的任何东西。

And that will match any SongName that contains a literal "=?" and I don't think that's anything like what you want.

A ％匹配的字符在SQL像任何序列，它在本质上是一样的。* 的一个普通的前pression;所以，如果你想匹配的开始，那么你不想要一个领先的％。此外，你的？占位符必须是单引号之外否则将PTED作为一个问号，而不是一个占位符间$ P $。

A % matches any sequence of characters in an SQL LIKE, it is essentially the same as .* in a regular expression; so, if you want to match at the beginning then you don't want a leading %. Also, your ? placeholder needs to be outside the single quotes or it will be interpreted as a literal question mark rather than a placeholder.

您想要更多的东西是这样的：

You want something more like this:

String[] a = new String[1];
a[0]       = match_str + '%';
Cursor   c = myDB.rawQuery("SELECT * FROM songs WHERE SongName LIKE ?", a);

如果你想成为真正严格也不得不逃离％和 _ 符号内 match_str 以及但是这将作为练习留给读者。

If you wanted to be really strict you'd also have to escape % and _ symbols inside match_str as well but that's left as an exercise for the reader.