https://github.com/debhere/leetcode-solutions

https://github.com/debhere/leetcode-solutions

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• Host: GitHub
• URL: https://github.com/debhere/leetcode-solutions
• Owner: debhere
• Created: 2023-06-02T04:28:44.000Z (over 1 year ago)
• Default Branch: master
• Last Pushed: 2024-04-22T12:47:11.000Z (7 months ago)
• Last Synced: 2024-04-22T12:58:32.854Z (7 months ago)
• Language: SQL
• Size: 23.4 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        

# This repository contains LeetCode solutions and certain learnings on the way forward...!!!

## Learnings

### SQL

1. Add below two lines in the gitattributes to include SQL in the language statistics.

	*.sql linguist-language=sql

	

	*.sql linguist-detectable=true

2. auto_increment in MySQL is similar to Identity() in SQL-Server.

3. Constraint naming inline to column declaration is not permissible in MySQL

```

Create Table Products

(product_id int Constraint PK_Products Primary Key Identity(1,1),

product_name varchar(100),

product_category varchar(50))

```

The above is a valid query in SQL-Server whereas in MySQL it becomes

```

Create Table Products

(product_id int Primary Key auto_increment,

product_name varchar(100),

product_category varchar(50));

```

4. Foreign key declaration for MySQL can only be done at the end of table declaration

```

Create Table Orders

(product_id int ,

order_date date,

unit int,

FOREIGN KEY (product_id) REFERENCES Products(product_id));

```

5. While inserting values into another table with foreign key constraints, MySQL throws an error until setting the below line.

```

SET FOREIGN_KEY_CHECKS=0;

```

6. Even for auto_increment, need to mention the column names the values being inserted

```

insert into Products (product_name, product_category) values

('Leetcode Solutions', 'Book'),

('Jewels of Stringology', 'Book'),

('HP', 'Laptop'),

('Lenovo', 'Laptop'),

('Leetcode Kit', 'T-shirt');

```

7. Wildcard characters like [], -, ^ does not work in MySQL. Instead one can use 'regexp' keyword for a pattern matching in the query in MySQL. Here is an example

```

select * from Users

where mail regexp '^[a-zA-Z][a-zA-Z0-9_.-]*@leetcode[.]com$';

```

8. Similar to ISNULL(expr, value) in SQL-Server, MySQL has IFNULL(expr, value) function that can return a specific value if the expression is NULL.

9. Display selected values as commas seperated string using function STRING_AGG() in SQL-Server and GROUP_CONCAT() in MySQL.

```

select sell_date, count(product) num_sold, STRING_AGG(product, ',') as products

from (select distinct * from Activities) T

group by sell_date

```

```

select sell_date, count(distinct product) num_sold, group_concat(distinct product order by product asc) products

from Activities

group by sell_date

```

### Python

1. say nums[] is an existing list. Now, nums[:] means creating a new list as nums but it is a not the same object but a different one.

2. O(logn) is common complexity, where there is a concept of halving or say to perform some action on next element based on some conditions.

3. int(n, 2) base 2 to convert to integer from binary.

4. := is a valid operator that allows assignment of variable within expressions.