如何在选择中的Android数据库查询和OR语句中搜索NULL

Question

关于数据库查询的几个问题:

所以我有以下数据库查询,它有一个WHERE语句,其中包含三个String变量(rackingSystem,制造商,"Amber Risk").

public Cursor fetchComponentsAndSpecForManufacturer(long inspectionId, String rackingSystem, String manufacturer) {
    Cursor mCursor =
            rmDb.query(true, DAMAGED_COMPONENTS_TABLE, new String[] {
                    DAMAGED_COMPONENT_ID,
                    LOCATION_LINK,
                    RUN_LINK,
                    AREA_LINK,
                    INSPECTION_LINK,
                    LOCATION_REF,
                    RACKING_SYSTEM,
                    COMPONENT,
                    COMPONENT_TYPE,
                    QUANTITY,
                    POSITION,
                    RISK,
                    ACTION_REQUIRED,
                    NOTES_GENERAL,
                    MANUFACTURER,
                    TEXT1,
                    TEXT2,
                    TEXT3,
                    TEXT4,
                    NOTES_SPEC,
                    SPEC_SAVED}, 
                    INSPECTION_LINK + " = " + inspectionId + " AND " + RACKING_SYSTEM + " = ? AND " + MANUFACTURER + " = ? AND " + RISK + " = ? ", 
                    new String[] {rackingSystem, manufacturer, "Amber Risk"},
                    COMPONENT_TYPE + ", " + TEXT1 + ", " + TEXT2 + ", " + TEXT3 + ", " + TEXT4 + ", " + NOTES_SPEC,
                    null, null, null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}

问题1:

我如何搜索NULL,因为在上面的例子中,制造商在数据库中可能是NULL(因为用户可能没有在该数据库中输入任何内容).

问题2:

我可以在WHERE语句中包含OR语句吗？所以目前我正在搜索所有"Amber Risk"的记录,但我还需要在此列表中包含"Red Risk"条目.如果我可以这样做,我应该如何编辑WHERE语句？

Answer 1

如何搜索NULL,因为在上面的示例中,制造商在数据库中可能为NULL

使用MANUFACTURER + " IS NULL".

我可以在WHERE语句中包含OR语句吗？

是.让我们搜索空或制造商:

MANUFACTURER + " IS NULL OR " + MANUFACTURER + " = ''"

所以目前我正在搜索所有"Amber Risk"的记录,但我还需要在此列表中包含"Red Risk"条目.

INSPECTION_LINK + " = " + inspectionId + " AND " + RACKING_SYSTEM + " = ? AND " + 
        MANUFACTURER + " IS NULL AND (" + RISK + " = ? OR " + RISK + " = ?)", 
new String[] {rackingSystem, manufacturer, "Amber Risk", "Red Risk"},