Replace returned null values in LEFT OUTER JOIN

问题

SELECT        WO_BreakerRail.ID, indRailType.RailType, indRailType.RailCode, WO_BreakerRail.CreatedPieces, WO_BreakerRail.OutsideSource, WO_BreakerRail.Charged, WO_BreakerRail.Rejected, WO_BreakerRail.RejectedToCrop, WO_BreakerRail.Date
FROM            indRailType LEFT OUTER JOIN
                         WO_BreakerRail ON indRailType.RailCode = WO_BreakerRail.RailCode AND WO_BreakerRail.Date = @date

When this returns, there are NULL values in the Date column where there are no matching rows from WO_BreakerRail. Is there a way to replace just those NULL values with @date?

回答1:

In oracle and sql server, you can use the COALESCE (oracle version) function

SELECT ...., COALESCE(WO_BreakerRail.Date, @date)

回答2:

You can use COALESCE function (go here for mysql documentation)

COALESCE(WO_BreakerRail.Date, @date)

or you can use a simple IF:

IF(WO_BreakerRail.Date IS NULL, @date, WO_BreakerRail.Date)

回答3:

Yes, just use COALESCE, eg. COALESCE(WO_BreakerRail.Date, @date)

回答4:

Actually, in MySQL there is a IFNULL() function.

select
  ifnull(wo_breakerrail.date, @date) as `date`,

来源：https://stackoverflow.com/questions/2507300/replace-returned-null-values-in-left-outer-join