CREATE TABLE stock (
    supplier_id INT,
    product_id INT,
    stock_quantity INT,
    record_date DATE
);

-- Insert the data
delete from stock;
INSERT INTO stock (supplier_id, product_id, stock_quantity, record_date)
VALUES
    (1, 1, 60, '2022-01-01'),
    (1, 1, 40, '2022-01-02'),
    (1, 1, 35, '2022-01-03'),
    (1, 1, 45, '2022-01-04'),
 (1, 1, 51, '2022-01-06'),
 (1, 1, 55, '2022-01-09'),
 (1, 1, 25, '2022-01-10'),
    (1, 1, 48, '2022-01-11'),
 (1, 1, 45, '2022-01-15'),
    (1, 1, 38, '2022-01-16'),
    (1, 2, 45, '2022-01-08'),
    (1, 2, 40, '2022-01-09'),
    (2, 1, 45, '2022-01-06'),
    (2, 1, 55, '2022-01-07'),
    (2, 2, 45, '2022-01-08'),
 (2, 2, 48, '2022-01-09'),
    (2, 2, 35, '2022-01-10'),
 (2, 2, 52, '2022-01-15'),
    (2, 2, 23, '2022-01-16');


select * from stock;

-- write an sql query to find the supllier id , rpdocut id, 
-- startindg date of record dateand no of days for which inventory is less 
-- than 50 for two or more consective days.



with cte as (
select  supplier_id, product_id, record_date , 
(record_date - lag(record_date,1, record_date) over(partition by supplier_id , product_id order by record_date))
as date_flg_lag

from stock 
where stock_quantity<50)

-- ideally i should use datediff 

, cte2 as (
select *, 
row_number() over() as rn 
from (
select *,
case when date_flg_lag >1 or date_flg_lag=0  then 1 else 0 end flg 
from cte ) x where flg = 1 )


, cte3 as (
select a.*, b.record_date as min_date, b.rn 

from cte a left join cte2 b on a.supplier_id=b.supplier_id and a.product_id=b.product_id
and b.record_date = a.record_date )




, cte4 as (
select *, 
sum(flg2) over(order by rn2) as bucket from (

select *, case when rn is null then 0 else 1 end as flg2 from (
select *, row_number()  over() as rn2 

from cte3 ) x ) y )
-- ) z group by bucket 

-- select * from cte4 


select supplier_id, product_id, min(record_date), count(rn2) as no_days from cte4 
group by 1,  2, bucket
having count(rn2)>=2
by

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About MySQL

MySQL is a open-source, free and very popular relational database management system which is developed, distributed and supported by Oracle corporation.

Key Features:

  • Open-source relational database management systems.
  • Reliable, very fast and easy to use database server.
  • Works on client-server model.
  • Highly Secure and Scalable
  • High Performance
  • High productivity as it uses stored procedures, triggers, views to write a highly productive code.
  • Supports large databases efficiently.
  • Supports many operating systems like Linux*,CentOS*, Solaris*,Ubuntu*,Windows*, MacOS*,FreeBSD* and others.

Syntax help

Commands

1. CREATE

CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

Example

CREATE TABLE EMPLOYEE (
  empId INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  dept TEXT NOT NULL
);

2. ALTER

ALTER TABLE Table_name ADD column_name datatype;

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Dave', 'Sales');

3. TRUNCATE

TRUNCATE table table_name;

4. DROP

DROP TABLE table_name;

5. RENAME

RENAME TABLE table_name1 to new_table_name1;

6. COMMENT

Single-Line Comments:

 --Line1;

Multi-Line comments:

   /* Line1,
   Line2 */

DML Commands

1. INSERT

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

Note: Column names are optional.

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Ava', 'Sales');

2. SELECT

SELECT column1, column2, ...
FROM table_name
[where condition];

Example

SELECT * FROM EMPLOYEE where dept ='sales';

3. UPDATE

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Example

UPDATE EMPLOYEE SET dept = 'Sales' WHERE empId='0001';

4. DELETE

DELETE FROM table_name where condition;

Example

DELETE from EMPLOYEE where empId='0001';

Indexes

1. CREATE INDEX

  CREATE INDEX index_name on table_name(column_name);
  • To Create Unique index:
  CREATE UNIQUE INDEX index_name on table_name(column_name);

2. DROP INDEX

DROP INDEX index_name ON table_name;

Views

1. Create a View

Creating a View:
CREATE VIEW View_name AS 
Query;

2. How to call view

SELECT * FROM View_name;

3. Altering a View

ALTER View View_name AS 
Query;

4. Deleting a View

DROP VIEW View_name;

Triggers

1. Create a Trigger

CREATE TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW [trigger_order] trigger_body
/* where
trigger_time: { BEFORE | AFTER }
trigger_event: { INSERT | UPDATE | DELETE }
trigger_order: { FOLLOWS | PRECEDES } */

2. Drop a Trigger

DROP TRIGGER [IF EXISTS] trigger_name;

Stored Procedures

1. Create a Stored Procedure

CREATE PROCEDURE sp_name(p1 datatype)
BEGIN
/*Stored procedure code*/
END;

2. How to call Stored procedure

CALL sp_name;

3. How to delete stored procedure

DROP PROCEDURE sp_name;

Joins

1. INNER JOIN

SELECT * FROM TABLE1 INNER JOIN TABLE2 where condition;

2. LEFT JOIN

SELECT * FROM TABLE1 LEFT JOIN TABLE2 ON condition;

3. RIGHT JOIN

SELECT * FROM TABLE1 RIGHT JOIN TABLE2 ON condition;

4. CROSS JOIN

SELECT select_list from TABLE1 CROSS JOIN TABLE2;