How to insert into a table? - sql

Question

Table Name: free_meals_bill
punch_date employee_id employee_name product_name
2021-02-22 12:15:50.086471 123456 john Variety Rice - Curd - Rs.35
2021-02-22 12:19:50.086472 234456 marry Variety Rice - Curd - Rs.35
2021-02-22 12:22:50.086473 355456 peter Variety Rice - Curd - Rs.35
Before inserting into "free_meals_bill" table, I want to check that per employee_id only one punch is allowed.
For example, if john (employee id 123456) is already in the free_meals_bill then again for the same date, john data should not be insert again into the "free_meals_bill" table.
Query:
insert into free_meals_bill (punch_date,employee_id,employee_name,product_name)
Values ('2021-02-22 10:15:50.086471',123456,'john','Variety Rice - Curd - Rs.35')
SELECT
employee_id,
COUNT(*) as count,
date_trunc('day',punch_date) as day
FROM bill_item
WHERE punch_date>= CURRENT_DATE
GROUP BY employee_id, day
HAVING COUNT(*) = 0

Answer 1

You can use a NOT EXISTS condition to check if the to be inserted values already exist:
insert into free_meals_bill (punch_date, employee_id, employee_name, product_name)
select *
from (
values (date '2021-02-22 10:15:50.086471',123456,'john','Variety Rice - Curd - Rs.35')
) as t(punch_date, employee_id, employee_name, product_name
where not exists (SELECT *
FROM free_meals_bill bi
WHERE bi.punch_date::date = t.punch_date::date
AND bi.employee_id = t.employee_id)
But if you only allow one row per (employee_id, punch_date) you should create a unique constraint or index
create unique index only_one_meal_per_day
on free_meals_bills ( (punch_date::date), employee_id);
Then you can do:
insert into free_meals_bill (punch_date, employee_id, employee_name, product_name)
values (date '2021-02-22 10:15:50.086471',123456,'john','Variety Rice - Curd - Rs.35')
on conflict ((punch_date::date), employee_id)
do nothing;

Answer 2

Your select statement has wrong column sequence, it should be the same sequence with your insert statement. date,id,name,product. And, should be the same number of columns too.

Answer 3

demo:db<>fiddle
You cannot use VALUES and SELECT in one INSERT statement. The SELECT statement replaces the VALUES part
You can use EXISTS to check for occurrences.
INSERT INTO free_meals_bill (punch_date,employee_id,employee_name,product_name)
SELECT
*
FROM bill_item
WHERE punch_date >= CURRENT_DATE
AND NOT EXISTS (
SELECT 1 FROM free_meals_bill WHERE employee_id = bill_item.employee_id
);
Note: I used * selector here, because in my example bill_item has the same columns as free_meals_bill. You have to adapt this to your real used case, of course, if it doesn't fit to something like this (depending on how bill_item actually looks like):
SELECT
punch_date,
employee_id,
employee_name,
product_name
...
Edit:
To avoid such duplication by table design you should think about adding a UNIQUE contraint to your table:
ALTER TABLE free_meals_bill ADD CONSTRAINT my_unique_constraint UNIQUE (employee_id);
This prevents INSERT statements from inserting duplicate records automatically, you don't need to do this with SELECT statements