How to store date and compare it in sql server? - sql

Question

basically, i need to make database for plants and their harvest dates.
For example, table with all the plants.
CREATE TABLE plant
(
plant_name NVARCHAR(20) NOT NULL
PRIMARY KEY ,
best_to_harvest_day INT NOT NULL ,
best_to_harvest_month NVARCHAR(15)
)
Example for plant entry: Rose 16 December
And another table called harvests
Where are multiple harvested plants and dates when they were harvested.
CREATE TABLE harvests
(
plant_name nvarchar(20) NOT NULL FOREIGN KEY REFERENCES plant(plant_name),
amount int NOT NULL,
havested_day int NOT NULL,
harvested_month nvarchar(15),
harvested year int NOT NULL
)
And this method does work, because i can make a sql query to compare which plants are harvested at their best time etc.
But isnt there a tidy way?
something like this: (using the date)
CREATE TABLE plant
(
plant_name NVARCHAR(20) NOT NULL
PRIMARY KEY ,
best_to_harvest DATE --But here should only be day and month, not year.
)
CREATE TABLE harvests
(
plant_name NVARCHAR(20) NOT NULL
FOREIGN KEY REFERENCES plant ( plant_name ) ,
amount INT NOT NULL ,
harvested DATE --But here i need full date year,day,month
)
Bottom line is that i need to compare them.
Okay, i think i can use EXTRACT(unit FROM date)
and then compare them but the question still stands, how to make plant table date not to consist of year?

Answer 1

First, store the date parts as numbers and check their values. This isn't perfect, but probably good enough:
CREATE TABLE plant (
plant_id int not null PRIMARY KEY,
plant_name nvarchar(20) NOT NULL UNIQUE,
best_to_harvest_day int NOT NULL,
best_to_harvest_month int not NULL,
check (best_to_harvest_day between 1 and 31),
check (best_to_harvest_month between 1 and 12)
);
Note the inclusion of an integer identity primary key. This is recommended, because integers are more efficient for foreign key references.
Then use date for the harvest:
CREATE TABLE harvests (
harvest_id int not null primary key,
plant_id int NOT NULL FOREIGN KEY REFERENCES plant(plant_id),
amount int NOT NULL,
harvested date --But here i need full date year,day,month
);
And you can do:
select h.*,
(case when p.best_to_harvest_day = day(h.harvest_day) and
p.best_to_harvest_month = month(h.harvest_month)
then 'Y' else 'N'
end)
from harvest h join
plant p
on h.plant_id = p.plant_id;