sqlite | 易学教程

How to find the length of a particular column of a table in javascript?

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问题 I am using sqlite database in my project. My table structure will be almost like this id cid values 1 1 value1 2 1 value2 3 1 value3 4 1 value4 5 2 value1 6 2 value2 7 3 value1 8 3 value2 9 3 value3 so I want all the values of the same cid ,how should I code it? My query: tx.executeSql("SELECT cid,value FROM table where cid="+cid_value, [], querySuccess, errorCB,cid_value); because,when I tried it the following manner, var details = results.rows.length; console.log("db test value:"+results

In Python's sqlite3 module, why can't cursor.rowcount() tell me the number of rows returned by a select statement

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问题 So I've read the documentation and it says: Cursor.rowcount¶ Although the Cursor class of the sqlite3 module implements this attribute, the database engine’s own support for the determination of “rows affected”/”rows selected” is quirky. This includes SELECT statements because we cannot determine the number of rows a query produced until all rows were fetched. How come, immediately after executing a SELECT, I can't use this to determine the number of rows returned. Surely the query, having

[743]python sqlite3.ProgrammingError: SQLite objects created in a thread can only be used

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错误 sqlite3.ProgrammingError: SQLite objects created in a thread can only be used in that same thread.The object was created in thread id 12096 and this is thread id 19564 引言: SQLite是基于文件系统的mini数据库，我们用以存放简便的数据，本文将描述在代码中碰到的并发问题。代码为多个线程进行数据库的读写操作。这里简要列出关键的数据库操作，主要集中在insert/update操作。问题分析从错误信息来分析，问题是sqlite本身应对多个线程并发访问过程中的冲突问题，由一个线程创建并访问的sqlite的数据库，无法允许另外一个线程进行访问。这里的解决办法可能有２个：通过队列规避多线程的访问通过设置或者多个访问管道，规避线程之间的冲突问题从技术上评估，２个方法都可以解决问题，哪种更具优势？问题解决通过网上搜索发现，其实可以通过设置sqlite文件的读取方式，可以简单规避掉线程之间的冲突问题： def initDB(self, file_path): self.file_path = file_path self.cx = sqlite3.connect(file_path, check_same

Accessing SQLite database in Unity with a coroutine

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问题 I've created a menu in Unity which is populated by results from an SQLite DB. However when I create the menu, the whole game freezes for a moment while it queries the DB. To fix this, I'm trying to separate the creation of the menu and the populating of it with data (i.e. the menu will just say "loading" until the query is complete). I have been trying to use a yield-return co-routine to do this but the game is still freezing. Below I have some pseudo-code illustrating what I am doing... void

How to get errors details from android.database.SQLException?

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问题 I have a database in my android app with two separate columns that have a UNIQUE constraint. When entering data and an SQLException exception is thrown I want to know which field's unique constraint was violated so I can take appropriate action. 回答1: The class java.lang.SQLException on which android.database.SQLException is based has methods int getErrorCode() and String getSQLState() which should be able to help you get details. 回答2: Database constraints are mostly intended to catch

How to get errors details from android.database.SQLException?

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How to deploy a database file with a Xamarin.from app?

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问题 I created a sqlite file in my project with some data in it, but I don't know how to link it to my app. I expect the data could be loaded on a Android simulator. I found a tutorial which was published in 2015, it works no longer, such as GetLocalFilePath function cannot be found after new a FileAccessHelper Class. And the tutorial project seemed using an olde version of SQLite.net-PCL package, because SQLite.Net.Platform.XamarinAndroid was used in the tutorial project, while this package is no

problems with update statement in SQLite

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问题 I have created a database using SQLite. I want to update the value of a "features" column( type Blob)...but i do not know how to write the "update" statement . This is what i tried: try { stat = conn.createStatement(); } catch (SQLException e) { } try { byte[] b = getFunction(); stat.executeUpdate("update table set features="+b); } catch (SQLException e) { } i get the follwing error : java.sql.SQLException: unrecognized token: "[B@13a317a" so i guess that "b" is the problem ? 回答1: Try this

SQLITE3 inserting a null value

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问题 sqlite3_bind_int(statement, 1, nil); How can I add a null in my above statement , as I am making this field auto increment. Here's my code : if (sqlite3_open([[self dataFilePath] UTF8String], &database)!= SQLITE_OK) { sqlite3_close(database); NSAssert(0, @"Failed to open database"); } NSLog(@"json count ========== %i",[jsonArray count]); for (int i =0 ; i < [jsonArray count]; i++) // while (i < [jsonArray count]) { dictionary = [jsonArray objectAtIndex:i]; char *errorMsg; sqlite3_stmt

HTML 5 SQLite: Multiple Inserts in One Transaction

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问题 Is it possible to do something like this: begin; insert into some_table (some_col, another_col) values ('a', 'b'); insert into some_table (some_col, another_col) values ('c', 'd'); ... commit; ...in HTML 5? With each transaction being async and having it's own callback, seems to me that it would be difficult to write a routine that inserts an unknown amount of rows, and then calls back when it has completed. 回答1: Here is sample code of how you do it. I tested in on recent versions of safari