[英]Why are no rows returned in my app, whereas the same query returns rows in DBBrowser?
通過對我的 SQLite 數據庫的這個簡單查詢:
SELECT MovieTitle, MPAARating, IMDBRating, DurationInMinutes, YearReleased, genres, actors, directors, screenwriters
FROM MOVIES_SINGLETABLE
WHERE IMDBRating >= @IMDBMinRating
ORDER BY IMDBRating DESC, YearReleased DESC LIMIT 1000
...我得到記錄:
但是有更多的過濾:
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
...我什么也沒得到(是的,所有這些參數都分配了適當的值,即:5.0、'1958'、'2019'、'Drama'、'Western' 和 'PG'):
然而,使用相同的查詢,我確實在 DBBrowser 中獲得了返回的記錄:
這里發生了什么? 為什么相同的查詢在我的應用程序中沒有返回任何內容,而是從 DBBrowser 返回大量內容?
根據大眾需求,以下是參數的分配方式( genresSelected是一個字符串列表):
if (GenresFiltered())
{
if (genresSelected.Count > 0)
{
cmd.Parameters.AddWithValue("@genre1", genresSelected[0].ToString());
}
if (genresSelected.Count > 1)
{
cmd.Parameters.AddWithValue("@genre2", genresSelected[1].ToString());
}
. . .
...在分配給參數之前的查詢字符串如下所示:
“從 MOVIES_SINGLETABLE 中選擇電影標題、MPAARating、IMDBRating、DurationInMinutes、YearReleased、流派、演員、導演、編劇,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"
最終的查詢查詢字符串現在是(刪除了單引號):
從 MOVIES_SINGLETABLE 中選擇電影標題、MPAARating、IMDBRating、DurationInMinutes、YearReleased、流派、演員、導演、編劇,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
我嘗試了以下所有排列,但都沒有返回任何數據:
"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)
- 與:
cmd.Parameters.AddWithValue("@genre1",string.Format("%{0}%",genresSelected[0].ToString())); cmd.Parameters.AddWithValue("@genre2",string.Format("%{0}%",genresSelected 1 .ToString()));
盡可能地結合 forpas 的想法,我能夠在 DBBrowser 中獲取返回的記錄,但尚未在實際的應用程序中返回。 注釋掉的行和下面用於過濾流派的現有行都有效。 如果沒有包含值的單引號,我得到了一個關於“Western”不是列名的 err msg,但是它周圍的單引號可以工作:
所以我嘗試了以下所有排列,但沒有一個返回任何記錄:
// @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' || '%')) ";
接下來的問題是,我想:我該如何產生,在C#,SQL同位,做在DBBrowser,即這條線的工作:
AND ((genres LIKE '%' || 'Western' || '%') OR (genres LIKE '%' || 'Drama' || '%'))
注意:這也不會返回任何內容:
AND ((genres LIKE @genre1) OR (genres LIKE @genre2))
在sql語句中,你傳遞的參數一定不能用單引號括起來。
還讓 SQLite 使用||
將'%'
通配符連接到參數操作員。 所以寫你的代碼是這樣的:
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND ((genres LIKE '%' || @genre1 || '%') OR (genres LIKE '%' || @genre2 || '%'))
AND (MPAARating = @mpaaRating1)
更新:
我看到您為流派添加了參數值,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。
這意味着不需要在 sql 語句中再次連接它們。
因此,將運算符LIKE
與參數一起使用,因為它們是:
WHERE IMDBRating >= @IMDBMinRating
AND (YearReleased BETWEEN @EarliestYear AND @LatestYear)
AND ((genres LIKE @genre1) OR (genres LIKE @genre2))
AND (MPAARating = @mpaaRating1)
我相信問題出在您的查詢中。 看起來您正在使用參數化查詢,因此您應該使用:
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");
在大多數應用層 SQL 參數化中,您必須在原始字符串上連接通配符,然后再將它們綁定到准備好的 SQL 語句。
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,准備好的語句中的所有參數通常都不用引號、通配符或其他符號括起來。
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
我終於讓它與這個一起工作:
return string.Format("AND instr(genres, '{0}') > 0 OR instr(genres, '{1}') > 0 ",
genresSelected[0].ToString(), genresSelected[1].ToString());
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.