iphone - 检查列是否已存在，如果不存在，则在sqlite中更改表

我想在我的应用程序中更改sqlite表。

现在，我想检查表中是否已存在该列？

因此，如果不存在，我想添加具有alter table syntex的列。

目前我正在使用。

-(void) alterDB{
    sqlite3_stmt *statement;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:DATABASE_NAME];

    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK)
    {

        NSString *updateSQL = [NSString stringWithFormat: @"ALTER TABLE diagramInfo ADD COLUMN testColumn VARCHAR"];
        const char *update_stmt = [updateSQL UTF8String];
        sqlite3_prepare_v2(database, update_stmt, -1, &statement, NULL);

        if(sqlite3_step(statement)==SQLITE_DONE)
        {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB altered" message:@"Success" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];
            [alert release];
            alert=nil;

        }
        else
        {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB Updation" message:@"DB not Altered" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];
            [alert release];
            alert=nil;
        }
        // Release the compiled statement from memory
        sqlite3_finalize(statement);
        sqlite3_close(database);
    }
}

最佳答案

使用以下功能检查列是否存在。实际上没有检查过，因此您可能必须检查语法。概念就像您能够创建准备好的语句，而不是存在的列一样，否则就不存在。

-(BOOL)checkColumnExists
{
    BOOL columnExists = NO;

    sqlite3_stmt *selectStmt;

    const char *sqlStatement = "select yourcolumnname from yourtable";
    if(sqlite3_prepare_v2(yourDbHandle, sqlStatement, -1, &selectStmt, NULL) == SQLITE_OK)
        columnExists = YES;

    return columnExists;
}

Swift 3.2:

private func tableHasColumn(db: OpaquePointer, tableName: String, columnName: String) -> Bool {

        var retVal = false

        var tableColumnsQueryStatement: OpaquePointer? = nil
        if sqlite3_prepare_v2(db, "PRAGMA table_info(\(tableName));",
                            -1,
                            &tableColumnsQueryStatement,
                            nil) == SQLITE_OK {

            while (sqlite3_step(tableColumnsQueryStatement) == SQLITE_ROW) {

                let queryResultCol1 = sqlite3_column_text(tableColumnsQueryStatement, 1)
                let currentColumnName = String(cString: queryResultCol1!)

                if currentColumnName == columnName {
                    retVal = true
                    break
                }
            }
        }

        return retVal
}