QSqlQuery不会返回带有QSqlQuery::bindValue的行，但如果我插入带有QString::arg的值

Question

我有一个对QSqlQuery的调用，当我使用QSqlQuery:：bindValue时，它不返回行，但当我用QString:：arg添加值时，它会返回行。

具体来说，这不会返回任何内容：

QSqlQuery q(QSqlDatabase::database( mDbAdapter->dbFilename() ));
q.prepare("select Focus.TextFormId as ID, Focus, TextForm, Gloss from (select TextFormId,group_concat( Transcription , ' ' ) as TextForm, group_concat( Gloss , '-' ) as Gloss from (select TextFormId,AllomorphId,Allomorph.Form as Transcription,LexicalEntryGloss.Form as Gloss from MorphologicalAnalysisMembers,Allomorph,LexicalEntryGloss where TextFormId in ( select TextFormId from MorphologicalAnalysisMembers where AllomorphId in (select _id from Allomorph where  LexicalEntryId=:LexicalEntryId and WritingSystem=:TextFormWS) ) and AllomorphId = Allomorph._id and Allomorph.LexicalEntryId = LexicalEntryGloss.LexicalEntryId and LexicalEntryGloss.WritingSystem=:GlossWS order by TextFormId, AllomorphOrder) group by TextFormId ) as Concatenation left join  ( select TextFormId, Form as Focus from Allomorph,MorphologicalAnalysisMembers on Allomorph._id=MorphologicalAnalysisMembers.AllomorphId and LexicalEntryId=:LexicalEntryId ) as Focus on Focus.TextFormId = Concatenation.TextFormId;");
q.bindValue(":LexicalEntryId", mLexicalEntryId);
q.bindValue(":GlossWS", mGlossWs.id());
q.bindValue(":TextFormWS", mTextFormWs.id());
if( !q.exec() )
    qWarning() << q.lastError().text() << q.executedQuery();

而这会返回正确的结果

QSqlQuery q(QSqlDatabase::database( mDbAdapter->dbFilename() ));
q.prepare(
        QString("select Focus.TextFormId as ID, Focus, TextForm, Gloss from (select TextFormId,group_concat( Transcription , ' ' ) as TextForm, group_concat( Gloss , '-' ) as Gloss from (select TextFormId,AllomorphId,Allomorph.Form as Transcription,LexicalEntryGloss.Form as Gloss from MorphologicalAnalysisMembers,Allomorph,LexicalEntryGloss where TextFormId in ( select TextFormId from MorphologicalAnalysisMembers where AllomorphId in (select _id from Allomorph where  LexicalEntryId=%1 and WritingSystem=%3) ) and AllomorphId = Allomorph._id and Allomorph.LexicalEntryId = LexicalEntryGloss.LexicalEntryId and LexicalEntryGloss.WritingSystem=%2 order by TextFormId, AllomorphOrder) group by TextFormId ) as Concatenation left join  ( select TextFormId, Form as Focus from Allomorph,MorphologicalAnalysisMembers on Allomorph._id=MorphologicalAnalysisMembers.AllomorphId and LexicalEntryId=%1 ) as Focus on Focus.TextFormId = Concatenation.TextFormId;")
        .arg(mLexicalEntryId).arg(mGlossWs.id()).arg(mTextFormWs.id())
        );
if( !q.exec() )
    qWarning() << q.lastError().text() << q.executedQuery();

复制整个数据库需要相当多的时间，但这里是一个更容易理解的查询形式：

select Focus.TextFormId as ID, Focus, TextForm, Gloss from (select TextFormId,group_concat( Transcription , ' ' ) as TextForm, group_concat( Gloss , '-' ) as Gloss
from 
(select TextFormId,AllomorphId,Allomorph.Form as Transcription,LexicalEntryGloss.Form as Gloss 
    from MorphologicalAnalysisMembers,Allomorph,LexicalEntryGloss 
    where TextFormId in 
        ( select TextFormId from MorphologicalAnalysisMembers where AllomorphId in 
            (select _id from Allomorph where  LexicalEntryId=%1 and WritingSystem=%3) ) 
        and AllomorphId = Allomorph._id 
        and Allomorph.LexicalEntryId = LexicalEntryGloss.LexicalEntryId 
        and LexicalEntryGloss.WritingSystem=%2 
        order by TextFormId, AllomorphOrder) 
    group by TextFormId ) as Concatenation 
    left join  
    ( select TextFormId, Form as Focus from Allomorph,MorphologicalAnalysisMembers 
        on Allomorph._id=MorphologicalAnalysisMembers.AllomorphId and LexicalEntryId=%1 ) 
    as Focus on Focus.TextFormId = Concatenation.TextFormId;

考虑到可能有改进查询的方法，我搜索了文档，没有发现任何迹象表明QSqlQuery:：bindValue有限制。

Answer 1

通过更改绑定值的方式，我最终能够将其用于绑定。如果我使用不同的占位符插入mLexicalEntryId两次（下面的第一个例子），或者如果我使用？绑定值的注释（下面的第二个示例）。尽管我更喜欢使用占位符，但对同一变量使用两个不同的占位符感觉很傻，所以我会坚持使用？符号

q.prepare("select Focus.TextFormId as ID, Focus, TextForm, Gloss from (select TextFormId,group_concat( Transcription , ' ' ) as TextForm, group_concat( Gloss , '-' ) as Gloss from (select TextFormId,AllomorphId,Allomorph.Form as Transcription,LexicalEntryGloss.Form as Gloss from MorphologicalAnalysisMembers,Allomorph,LexicalEntryGloss where TextFormId in ( select TextFormId from MorphologicalAnalysisMembers where AllomorphId in (select _id from Allomorph where  LexicalEntryId=:One and WritingSystem=:Three) ) and AllomorphId = Allomorph._id and Allomorph.LexicalEntryId = LexicalEntryGloss.LexicalEntryId and LexicalEntryGloss.WritingSystem=:Two order by TextFormId, AllomorphOrder) group by TextFormId ) as Concatenation left join  ( select TextFormId, Form as Focus from Allomorph,MorphologicalAnalysisMembers on Allomorph._id=MorphologicalAnalysisMembers.AllomorphId and LexicalEntryId=:Four ) as Focus on Focus.TextFormId = Concatenation.TextFormId;");
q.bindValue(":One", mLexicalEntryId);
q.bindValue(":Two", mGlossWs.id());
q.bindValue(":Three", mTextFormWs.id());
q.bindValue(":Four", mLexicalEntryId);
q.prepare("select Focus.TextFormId as ID, Focus, TextForm, Gloss from (select TextFormId,group_concat( Transcription , ' ' ) as TextForm, group_concat( Gloss , '-' ) as Gloss from (select TextFormId,AllomorphId,Allomorph.Form as Transcription,LexicalEntryGloss.Form as Gloss from MorphologicalAnalysisMembers,Allomorph,LexicalEntryGloss where TextFormId in ( select TextFormId from MorphologicalAnalysisMembers where AllomorphId in (select _id from Allomorph where  LexicalEntryId=? and WritingSystem=?) ) and AllomorphId = Allomorph._id and Allomorph.LexicalEntryId = LexicalEntryGloss.LexicalEntryId and LexicalEntryGloss.WritingSystem=? order by TextFormId, AllomorphOrder) group by TextFormId ) as Concatenation left join  ( select TextFormId, Form as Focus from Allomorph,MorphologicalAnalysisMembers on Allomorph._id=MorphologicalAnalysisMembers.AllomorphId and LexicalEntryId=? ) as Focus on Focus.TextFormId = Concatenation.TextFormId;");
q.addBindValue(mLexicalEntryId);
q.addBindValue(mTextFormWs.id());
q.addBindValue(mGlossWs.id());
q.addBindValue(mLexicalEntryId);