-- 10/15

tee 2024_10_15_sql_log.txt
use toyu;

-- Simulating Cartesian Product in MySQL.
SELECT s.*, e.*
FROM student AS s CROSS JOIN enroll AS e;

-- Simulating thta-join in MySQL.
SELECT s.*, e.*
FROM student AS s CROSS JOIN enroll AS ON (theta-condition);

-- Simulating equi-join in MySQL.
SELECT s.*, e.*
FROM student AS s CROSS JOIN enroll AS e USING(stuId);


-- Natural join

SELECT s.*, e.classId, e.grade, e.n_alerts
FROM student AS s CROSS JOIN enroll AS e USING(stuId);

SELECT *
FROM student AS s NATURAL JOIN enroll AS e;

EXPLAIN SELECT *
FROM student AS s NATURAL JOIN enroll AS e;

-- Prepared statements.
SET @sql = "SELECT * FROM toyu.student";
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

-- with placeholders.
SET @sql = "SELECT * FROM toyu.student WHERE major = ? AND ach >= ?";
PREPARE stmt FROM @sql;
SET @major = 'CSCI';
SET @ach = 38;
EXECUTE stmt USING @major, @ach;

EXECUTE stmt USING 'CSCI', 38;

SET @major = 'CINF';
SET @ach = 15;
EXECUTE stmt USING @major, @ach;

SET @major = 'ITEC';
SET @ach = 25;
EXECUTE stmt USING @major, @ach;

DEALLOCATE PREPARE stmt;

-- View

CREATE OR REPLACE VIEW school_summary(
   schoolCode, schoolName, n_departments) AS
SELECT s.schoolCode, s.schoolName,
COUNT(d.deptCode) AS n_departments
FROM school AS s LEFT JOIN department AS d ON (s.schoolCode = d.schoolCode)
GROUP BY s.schoolCode, s.schoolName;

SHOW CREATE VIEW school_summary;
-- Note something like "ALGORITHM=UNDEFINED DEFINER=`yue`@`localhost` SQL SECURITY DEFINER"
-- (default values) may be added.
DESC school_summary;

SELECT *
FROM school_summary
WHERE n_departments > 0;


DROP VIEW school_summary;


-- A very simple stored procedure.
-- Redefine the delimiter to end the procedure. Default delimiter: ;
DELIMITER $$

CREATE OR REPLACE PROCEDURE deptInfo(IN dCode VARCHAR(4), OUT numFaculty INT)
-- IN: pass by value.
BEGIN
   --  Display some information.
   SELECT d.deptName, d.SchoolCode, t1.n_majors, t2.n_minors
   FROM department AS d INNER JOIN
      (SELECT COUNT(stuId) AS n_majors
      FROM student
      WHERE major = dCode) AS t1 INNER JOIN
      (SELECT COUNT(stuId) AS n_minors
      FROM student
      WHERE minor = dCode) AS t2
   WHERE d.deptCode = dCode;

   -- MySQL does not direct sending output to console.
   -- It is necessary to use a SQL statement.
   SELECT 'Debuggin comment can be put here.';
   SELECT CONCAT('Faculty in the department: ', dCode) AS faculty;

   SELECT *
   FROM faculty AS f
   WHERE f.deptCode = dCode;

   SELECT COUNT(f.facId) INTO numFaculty
   FROM faculty AS f
   WHERE f.deptCode = dCode;
END $$

DELIMITER ;

SHOW CREATE PROCEDURE deptInfo;

SET @numFaculty = 0;
SET @dCode = 'CSCI';
CALL deptInfo('CSCI', @numFaculty);
SELECT @dCode, @numFaculty;

SET @dCode = 'ITEC';
CALL deptInfo(@dCode, @numFaculty);
SELECT @dCode, @numFaculty;

DROP PROCEDURE deptInfo;