[英]Why are no rows returned in my app, whereas the same query returns rows in DBBrowser?
通过对我的 SQLite 数据库的这个简单查询:
SELECT MovieTitle, MPAARating, IMDBRating, DurationInMinutes, YearReleased, genres, actors, directors, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000
...我得到记录:
但是有更多的过滤:
SELECT MovieTitle, MPAARating, IMDBRating, DurationInMinutes, YearReleased, genres, actors, directors, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND (genres LIKE '%@genre1%' OR genres LIKE '%@genre2%')
AND (MPAARating = '@mpaaRating1')
ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000
...我什么也没得到(是的,所有这些参数都分配了适当的值,即:5.0、'1958'、'2019'、'Drama'、'Western' 和 'PG'):
然而,使用相同的查询,我确实在 DBBrowser 中获得了返回的记录:
这里发生了什么? 为什么相同的查询在我的应用程序中没有返回任何内容,而是从 DBBrowser 返回大量内容?
根据大众需求,以下是参数的分配方式( genresSelected是一个字符串列表):
if (GenresFiltered())
{
if (genresSelected.Count > 0)
{
cmd.Parameters.AddWithValue("@genre1", genresSelected[0].ToString());
}
if (genresSelected.Count > 1)
{
cmd.Parameters.AddWithValue("@genre2", genresSelected[1].ToString());
}
. . .
...在分配给参数之前的查询字符串如下所示:
“从 MOVIES_SINGLETABLE 中选择电影标题、MPAARating、IMDBRating、DurationInMinutes、YearReleased、流派、演员、导演、编剧,其中 IMDBRating >= @IMDBMinRating AND YearReleased BETWEEN @EarliestYear 和 @LatestYear AND(流派 LIKE LIKE%'%s@genre @genre2%' OR 流派 LIKE '%@genre3%' OR 流派 LIKE '%@genre4%' OR 流派 LIKE '%@genre5%' OR 流派 LIKE '%@genre6%' OR 流派 LIKE '%@genre7%' OR流派 LIKE '%@genre8%' OR 流派 LIKE '%@genre9%') AND (MPAARating LIKE '%@mpaaRating1%') ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000"
最终的查询查询字符串现在是(删除了单引号):
从 MOVIES_SINGLETABLE 中选择电影标题、MPAARating、IMDBRating、DurationInMinutes、YearReleased、流派、演员、导演、编剧,其中 IMDBRating >= @IMDBMinRating AND(YearReleased BETWEEN @EarliestYear AND @LatestYear)AND(流派 LIKE2 流派)AND(流派 LIKE2 流派) MPAARating = @mpaaRating1) ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000
我尝试了以下所有排列,但都没有返回任何数据:
"AND (genres = @genre1 OR genres = @genre2) "
"AND ((genres = @genre1) OR (genres = @genre2)) "
"AND ((genres LIKE '%' || @genre1 || '%') OR (genres LIKE '%' || @genre2 || '%')) "
AND (genres LIKE '%'+@genre1+'%' OR genres LIKE '%'+@genre2+'%')
AND (genres LIKE @genre1 OR genres LIKE @genre2)
- 与:
cmd.Parameters.AddWithValue("@genre1",string.Format("%{0}%",genresSelected[0].ToString())); cmd.Parameters.AddWithValue("@genre2",string.Format("%{0}%",genresSelected 1 .ToString()));
尽可能地结合 forpas 的想法,我能够在 DBBrowser 中获取返回的记录,但尚未在实际的应用程序中返回。 注释掉的行和下面用于过滤流派的现有行都有效。 如果没有包含值的单引号,我得到了一个关于“Western”不是列名的 err msg,但是它周围的单引号可以工作:
所以我尝试了以下所有排列,但没有一个返回任何记录:
// @genre1 and @genre2 not surrounded by single quotes
return "AND ((genres LIKE '%' || @genre1 || '%') OR (genres LIKE '%' || @genre2 || '%')) ";
// @genre1 and @genre2 surrounded by single quotes
return "AND ((genres LIKE '%' || '@genre1' || '%') OR (genres LIKE '%' || '@genre2' || '%')) ";
// @genre1 and @genre2 not surrounded by single quotes, string prepended with "@"
return @"AND ((genres LIKE '%' || @genre1 || '%') OR (genres LIKE '%' || @genre2 || '%')) ";
// @genre1 and @genre2 surrounded by single quotes, string prepended with "@"
return @"AND ((genres LIKE '%' || '@genre1' || '%') OR (genres LIKE '%' || '@genre2' || '%')) ";
接下来的问题是,我想:我该如何产生,在C#,SQL同位,做在DBBrowser,即这条线的工作:
AND ((genres LIKE '%' || 'Western' || '%') OR (genres LIKE '%' || 'Drama' || '%'))
注意:这也不会返回任何内容:
AND ((genres LIKE @genre1) OR (genres LIKE @genre2))
在sql语句中,你传递的参数一定不能用单引号括起来。
还让 SQLite 使用||
将'%'
通配符连接到参数操作员。 所以写你的代码是这样的:
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND ((genres LIKE '%' || @genre1 || '%') OR (genres LIKE '%' || @genre2 || '%'))
AND (MPAARating = @mpaaRating1)
更新:
我看到您为流派添加了参数值,如下所示:
cmd.Parameters.AddWithValue("@genre1",string.Format("%{0}%", genresSelected[0].ToString()));
所以你在字符串中包含通配符。
这意味着不需要在 sql 语句中再次连接它们。
因此,将运算符LIKE
与参数一起使用,因为它们是:
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND ((genres LIKE @genre1) OR (genres LIKE @genre2))
AND (MPAARating = @mpaaRating1)
我相信问题出在您的查询中。 看起来您正在使用参数化查询,因此您应该使用:
var query = "SELECT MovieTitle, MPAARating, IMDBRating, DurationInMinutes, YearReleased, genres, actors, directors, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND (genres LIKE '%'+@genre1+'%' OR genres LIKE '%'+@genre2+'%')
AND (MPAARating = @mpaaRating1)
ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000";
...
cmd.Parameters.AddWithValue("@genre1","gener1");
cmd.Parameters.AddWithValue("@genre2","gener2");
cmd.Parameters.AddWithValue("@mpaaRating1","rating");
或者
var query = "SELECT MovieTitle, MPAARating, IMDBRating, DurationInMinutes, YearReleased, genres, actors, directors, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND (genres LIKE @genre1 OR genres LIKE @genre2)
AND (MPAARating = @mpaaRating1)
ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000";
...
cmd.Parameters.AddWithValue("@genre1","%gener1%");
cmd.Parameters.AddWithValue("@genre2","%gener2%");
cmd.Parameters.AddWithValue("@mpaaRating1","rating");
在大多数应用层 SQL 参数化中,您必须在原始字符串上连接通配符,然后再将它们绑定到准备好的 SQL 语句。
if (GenresFiltered())
{
if (genresSelected.Count > 0)
{
cmd.Parameters.AddWithValue("@genre1", "%" + genresSelected[0].ToString() + "%");
// cmd.Parameters.AddWithValue("@genre1", String.concat("%", genresSelected[0].ToString(), "%"));
}
if (genresSelected.Count > 1)
{
cmd.Parameters.AddWithValue("@genre2", "%" + genresSelected[1].ToString() "%");
// cmd.Parameters.AddWithValue("@genre2", String.concat("%", genresSelected[1].ToString(), "%"));
}
. . .
此外,准备好的语句中的所有参数通常都不用引号、通配符或其他符号括起来。
SELECT MovieTitle
, MPAARating
, IMDBRating
, DurationInMinutes
, YearReleased
, genres
, actors
, directors
, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND (genres LIKE @genre1 OR genres LIKE @genre2)
AND (MPAARating = @mpaaRating1)
ORDER BY IMDBRating DESC, YearReleased DESC
LIMIT 1000
我终于让它与这个一起工作:
return string.Format("AND instr(genres, '{0}') > 0 OR instr(genres, '{1}') > 0 ",
genresSelected[0].ToString(), genresSelected[1].ToString());
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