Modifying width and precision of database using QGIS?

You should import a csv file containing your data together with a csvt file containing the type of your data. For each column of your csv the corrensponfing column of the csvt should contain the type, such as "Real","Integer", "String". You can also specify width and precision of your data includinf the following info: "Real(2.12)","Integer(3)","String(10)".