Question

查询： UPDATE item_table SET field1=field1_spanish, field2=field2_spanish;

问题：如果<{strong> field1不为空，我如何使用field1_spanish 更新field1_spanish？如果field2不为空，我也希望field2_spanish更新field2_spanish。

谢谢！

Answer 1

http://sqlfiddle.com/#!5/58554/1

update
  item_table
set
  field1 = coalesce(field1_spanish, field1),
  field2 = coalesce(field2_spanish, field2)

coalesce()函数将返回传递给它的第一个参数，该参数不为null。所以在这种情况下，由于field2_spanish为null，它会将field2设置为field2（基本上什么都不做）。

要支持空字符串和NULL值，请尝试以下操作： http://sqlfiddle.com/#!5/b344f/3

update
  item_table
set
  field1 = case when coalesce(field1_spanish, '') = '' then
            field1
           else
            field1_spanish
           end,
  field2 =  case when coalesce(field2_spanish, '') = '' then
            field2
           else
            field2_spanish
           end

Answer 2

假设所有这些列都在同一个表中：

update some_table
set field1=field1_spanish,
field2=field2_spanish
where field1_spanish is not null
and field2_spanish is not null;

如果field1和field2位于table且*_spanish列位于table_spanish，那么......好，SQLite doesn't support a from clause in an update statement，所以你必须做一个相关的子查询。假设table的主键id由table_spanish引用，您可以执行以下操作：

update table a
set field1=(select s.field1_spanish 
    from table_spanish s 
    where field1_spanish is not null
    and s.id=a.id),
field2=(select s.field2_spanish 
    from table_spanish s 
    where field2_spanish is not null
    and s.id=a.id);

或者您可以通过连接填充临时表，然后从table中删除相关条目并从临时表中插入新数据（确保使用所有这些的事务！）。

Hat tip to martin clayton第二种方法。

SQLite仅在值不为空时更新列

2 个答案: