I have such code: (on RoR):
我有这样的代码:(在RoR上):
@types = Type.where("TYP_MOD_ID = ? AND (SUBSTRING(TYP_PCON_START,1,4) <= ?) AND (SUBSTRING(TYP_PCON_END,1,4) >= ?) AND TYP_KV_FUEL_DES_ID = ? ", params[:models], params[:year], params[:year], params[:fueltype]).order("TYP_HP_FROM")
But sometimes TYP_PCON_END is null in db.... How in such case use not null, but my value, sended by ruby (date.now(YEAR))?
但有时TYP_PCON_END在db中是空的....在这种情况下如何使用not null,但是我的值,由ruby(date.now(YEAR))发出?
So how if field is null use another value? How to check on null, and use my code if not null (SUBSTRING(TYP_PCON_END,1,4) >= ?) and another:
那么如果field为null又如何使用另一个值呢?如何检查null,如果不为null则使用我的代码(SUBSTRING(TYP_PCON_END,1,4)> =?)和另一个:
? >= ?
if null?
1 个解决方案
#1
0
You can use COALESCE:
你可以使用COALESCE:
SUBSTRING(COALESCE(TYP_PCON_END, 'some default string'),1,4) > ?
If you don't need the substring for your default value, then you would just do it this way:
如果您不需要子字符串作为默认值,那么您只需这样做:
COALESCE(SUBSTRING(TYP_PCON_END,1,4), 'AAAA') > ?
This works since doing a SUBSTRING on a null value will yield null as well.
这是有效的,因为对空值执行SUBSTRING也将产生null。
#1
0
You can use COALESCE:
你可以使用COALESCE:
SUBSTRING(COALESCE(TYP_PCON_END, 'some default string'),1,4) > ?
If you don't need the substring for your default value, then you would just do it this way:
如果您不需要子字符串作为默认值,那么您只需这样做:
COALESCE(SUBSTRING(TYP_PCON_END,1,4), 'AAAA') > ?
This works since doing a SUBSTRING on a null value will yield null as well.
这是有效的,因为对空值执行SUBSTRING也将产生null。