Adding conditions to Triggers in SQL Server - sql

Question

I have these tables in my SQL Server database:
CREATE TABLE weather
(
weatherId integer Identity(1,1) primary key,
weatherDate datetime,
rainout BIT,
temperature float,
inchesOfRain float
)
CREATE TABLE weather_audit
(
weatherAuditId integer Identity(1,1) primary key,
weatherId integer,
date datetime,
rainout BIT,
temperature float,
inchesOfRain float
)
CREATE TABLE maintenance
(
maintenanceId integer Identity(1,1) primary key,
maintenanceDescription nvarchar(100),
dateRequested datetime,
dateResolved datetime,
currentStatus nvarchar(20),
estimatedCost decimal,
)
CREATE TABLE maintenence_audit
(
mainteneceAuditId integer Identity(1,1) primary key,
maintenanceId integer,
description nvarchar(100),
dateRequested datetime,
dateResolved datetime,
currentStatus nvarchar(20),
estimatedCost decimal,
updatedOn datetime
)
I want to set up a trigger which fires when a row is inserted into the weather table whose inchesOfRain is > 4. This is what I have now, but it isn't working:
CREATE TRIGGER tr_weather_ForInsertUpdate
ON weather
FOR INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
IF (SELECT TOP 1 inchesOfRain FROM weather) > 4
INSERT INTO weather_audit (weatherId, weatherDate, rainout, temperature, inchesOfRain)
SELECT
i.weatherId, i.weatherDate, i.rainout, i.temperature, i.inchesOfRain
FROM
Inserted AS I
END
So if I were to insert this
INSERT INTO dbo.weather (weatherDate, rainout, temperature, inchesOfRain)
VALUES ('4/21/2018', '0', '70', '6');
it would add a row to the weather table and also to the weather_audit table since the inches of rain is 6

Answer 1

You need to depend on your Inserted pseudo table to make the decision whether or not to add a row to the audit table - try this:
CREATE TRIGGER tr_weather_ForInsertUpdate
ON weather
FOR INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
INSERT INTO weather_audit (weatherId, weatherDate, rainout, temperature, inchesOfRain)
SELECT
i.weatherId, i.weatherDate, i.rainout, i.temperature, i.inchesOfRain
FROM
Inserted AS I
WHERE
i.inchesOfRain > 4 -- just insert those rows with inchesOfRain > 4
END

Answer 2

Your trigger is all good, it just needs to be
CREATE TRIGGER tr_weather_ForInsertUpdate
ON weather
FOR INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
--Modified Code Start
DECLARE #inchesOfRain float
SELECT #inchesOfRain = inchesOfRain FROM inserted
IF #inchesOfRain > 4
BEGIN
---------------Modified COde End
INSERT INTO weather_audit (weatherId, weatherDate, rainout, temperature, inchesOfRain)
SELECT
i.weatherId, i.weatherDate, i.rainout, i.temperature, i.inchesOfRain
FROM
Inserted AS I
END
END
Update: Marc S code snippet is the perfect answer.