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Medium/Evaluate Boolean Expressions.sql

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+-- Question 78
+-- Table Variables:
+
+-- +---------------+---------+
+-- | Column Name   | Type    |
+-- +---------------+---------+
+-- | name          | varchar |
+-- | value         | int     |
+-- +---------------+---------+
+-- name is the primary key for this table.
+-- This table contains the stored variables and their values.
+ 
+
+-- Table Expressions:
+
+-- +---------------+---------+
+-- | Column Name   | Type    |
+-- +---------------+---------+
+-- | left_operand  | varchar |
+-- | operator      | enum    |
+-- | right_operand | varchar |
+-- +---------------+---------+
+-- (left_operand, operator, right_operand) is the primary key for this table.
+-- This table contains a boolean expression that should be evaluated.
+-- operator is an enum that takes one of the values ('<', '>', '=')
+-- The values of left_operand and right_operand are guaranteed to be in the Variables table.
+ 
+
+-- Write an SQL query to evaluate the boolean expressions in Expressions table.
+
+-- Return the result table in any order.
+
+-- The query result format is in the following example.
+
+-- Variables table:
+-- +------+-------+
+-- | name | value |
+-- +------+-------+
+-- | x    | 66    |
+-- | y    | 77    |
+-- +------+-------+
+
+-- Expressions table:
+-- +--------------+----------+---------------+
+-- | left_operand | operator | right_operand |
+-- +--------------+----------+---------------+
+-- | x            | >        | y             |
+-- | x            | <        | y             |
+-- | x            | =        | y             |
+-- | y            | >        | x             |
+-- | y            | <        | x             |
+-- | x            | =        | x             |
+-- +--------------+----------+---------------+
+
+-- Result table:
+-- +--------------+----------+---------------+-------+
+-- | left_operand | operator | right_operand | value |
+-- +--------------+----------+---------------+-------+
+-- | x            | >        | y             | false |
+-- | x            | <        | y             | true  |
+-- | x            | =        | y             | false |
+-- | y            | >        | x             | true  |
+-- | y            | <        | x             | false |
+-- | x            | =        | x             | true  |
+-- +--------------+----------+---------------+-------+
+-- As shown, you need find the value of each boolean exprssion in the table using the variables table.
+
+-- Solution
+with t1 as(
+select e.left_operand, e.operator, e.right_operand, v.value as left_val, v_1.value as right_val
+from expressions e
+join variables v
+on v.name = e.left_operand 
+join variables v_1
+on v_1.name = e.right_operand)
+
+select t1.left_operand, t1.operator, t1.right_operand,
+case when t1.operator = '<' then (select t1.left_val< t1.right_val)
+when t1.operator = '>' then (select t1.left_val > t1.right_val)
+when t1.operator = '=' then (select t1.left_val = t1.right_val)
+else FALSE
+END AS VALUE
+from t1

Medium/Find the start and end number of continuous ranges.sql

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+-- Question 80
+-- Table: Logs
+
+-- +---------------+---------+
+-- | Column Name   | Type    |
+-- +---------------+---------+
+-- | log_id        | int     |
+-- +---------------+---------+
+-- id is the primary key for this table.
+-- Each row of this table contains the ID in a log Table.
+
+-- Since some IDs have been removed from Logs. Write an SQL query to find the start and end number of continuous ranges in table Logs.
+
+-- Order the result table by start_id.
+
+-- The query result format is in the following example:
+
+-- Logs table:
+-- +------------+
+-- | log_id     |
+-- +------------+
+-- | 1          |
+-- | 2          |
+-- | 3          |
+-- | 7          |
+-- | 8          |
+-- | 10         |
+-- +------------+
+
+-- Result table:
+-- +------------+--------------+
+-- | start_id   | end_id       |
+-- +------------+--------------+
+-- | 1          | 3            |
+-- | 7          | 8            |
+-- | 10         | 10           |
+-- +------------+--------------+
+-- The result table should contain all ranges in table Logs.
+-- From 1 to 3 is contained in the table.
+-- From 4 to 6 is missing in the table
+-- From 7 to 8 is contained in the table.
+-- Number 9 is missing in the table.
+-- Number 10 is contained in the table.
+
+-- Solution
+select min(log_id) as start_id, max(log_id) as end_id
+from(
+select log_id, log_id-row_number() over (order by log_id) as rk
+from logs) a
+group by rk

Medium/Rectangles Area.sql

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+-- Question 79
+-- Table: Points
+
+-- +---------------+---------+
+-- | Column Name   | Type    |
+-- +---------------+---------+
+-- | id            | int     |
+-- | x_value       | int     |
+-- | y_value       | int     |
+-- +---------------+---------+
+-- id is the primary key for this table.
+-- Each point is represented as a 2D Dimensional (x_value, y_value).
+-- Write an SQL query to report of all possible rectangles which can be formed by any two points of the table. 
+
+-- Each row in the result contains three columns (p1, p2, area) where:
+
+-- p1 and p2 are the id of two opposite corners of a rectangle and p1 < p2.
+-- Area of this rectangle is represented by the column area.
+-- Report the query in descending order by area in case of tie in ascending order by p1 and p2.
+
+-- Points table:
+-- +----------+-------------+-------------+
+-- | id       | x_value     | y_value     |
+-- +----------+-------------+-------------+
+-- | 1        | 2           | 8           |
+-- | 2        | 4           | 7           |
+-- | 3        | 2           | 10          |
+-- +----------+-------------+-------------+
+
+-- Result table:
+-- +----------+-------------+-------------+
+-- | p1       | p2          | area        |
+-- +----------+-------------+-------------+
+-- | 2        | 3           | 6           |
+-- | 1        | 2           | 2           |
+-- +----------+-------------+-------------+
+
+-- p1 should be less than p2 and area greater than 0.
+-- p1 = 1 and p2 = 2, has an area equal to |2-4| * |8-7| = 2.
+-- p1 = 2 and p2 = 3, has an area equal to |4-2| * |7-10| = 6.
+-- p1 = 1 and p2 = 3 It's not possible because the rectangle has an area equal to 0.
+
+-- Solution
+select p1.id as p1, p2.id as p2, abs(p1.x_value-p2.x_value)*abs(p1.y_value-p2.y_value) as area
+from points p1 cross join points p2
+where p1.x_value!=p2.x_value and p1.y_value!=p2.y_value and p1.id<p2.id
+order by area desc, p1, p2