SQL/MySQL/Procedure Function/Introduction

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Recursion

   <source lang="sql">

mysql> Functions and procedures can call themselves. mysql> mysql> delimiter $$ mysql> CREATE FUNCTION factorial(n BIGINT) RETURNS BIGINT 

   -> BEGIN
   ->   IF n>=2 THEN
   ->     RETURN n * factorial(n-1);
   ->   ELSE
   ->     RETURN n;
   ->   END IF;
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> delimiter ; mysql> mysql> mysql> SELECT factorial(3); ERROR 1424 (HY000): Recursive stored functions and triggers are not allowed. mysql> mysql> drop function factorial; Query OK, 0 rows affected (0.00 sec) 

       </source>


Use user-defined function in a select statement to deal with data in a table

   <source lang="sql">

mysql> mysql> mysql> CREATE TABLE Employee( 

   ->     id            int,
   ->     first_name    VARCHAR(15),
   ->     last_name     VARCHAR(15),
   ->     start_date    DATE,
   ->     end_date      DATE,
   ->     salary        FLOAT(8,2),
   ->     city          VARCHAR(10),
   ->     description   VARCHAR(15)
   -> );

Query OK, 0 rows affected (0.03 sec) mysql> mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->              values (1,"Jason",    "Martin",  "19960725",  "20060725", 1234.56, "Toronto",  "O");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(2,"Alison",   "Mathews",  "19760321", "19860221", 6661.78, "Vancouver","O");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(3,"James",    "Smith",    "19781212", "19900315", 6544.78, "Vancouver","U");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(4,"Celia",    "Rice",     "19821024", "19990421", 2344.78, "Vancouver","U");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(5,"Robert",   "Black",    "19840115", "19980808", 2334.78, "Vancouver","Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(6,"Linda",    "Green",    "19870730", "19960104", 4322.78,"New York",  "N");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(7,"David",    "Larry",    "19901231", "19980212", 7897.78,"New York",  "N");

Query OK, 1 row affected (0.01 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(8,"James",    "Cat",     "19960917",  "20020415", 1232.78,"Vancouver", "N");

Query OK, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | O | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | O | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | U | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | U | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | N | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | N | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | N | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.02 sec) mysql> mysql> mysql> mysql> delimiter $$ mysql> mysql> CREATE FUNCTION cust_status(in_status CHAR(1)) 

   ->      RETURNS VARCHAR(20)
   -> BEGIN
   ->      DECLARE long_status VARCHAR(20);
   ->
   ->      IF in_status = "O" THEN
   ->           SET long_status="Overdue";
   ->      ELSEIF in_status = "U" THEN
   ->           SET long_status="Up to date";
   ->      ELSEIF in_status = "N" THEN
   ->           SET long_status="New";
   ->      END IF;
   ->
   ->      RETURN(long_status);
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> mysql> delimiter ; mysql> mysql> SELECT cust_status(description) as Status, count(*) as Count 

   ->   FROM employee
   ->  GROUP BY description
   ->  ORDER BY cust_status(description);

+------------+-------+ | Status | Count | +------------+-------+ | NULL | 1 | | New | 3 | | Overdue | 2 | | Up to date | 2 | +------------+-------+ 4 rows in set, 1 warning (0.00 sec) mysql> mysql> drop function cust_status; Query OK, 0 rows affected (0.00 sec) mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.00 sec) 

       </source>


Use user-defined function in order by clause

   <source lang="sql">

mysql> mysql> mysql> mysql> CREATE TABLE Employee( 

   ->     id            int,
   ->     first_name    VARCHAR(15),
   ->     last_name     VARCHAR(15),
   ->     start_date    DATE,
   ->     end_date      DATE,
   ->     salary        FLOAT(8,2),
   ->     city          VARCHAR(10),
   ->     description   VARCHAR(15)
   -> );

Query OK, 0 rows affected (0.03 sec) mysql> mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->              values (1,"Jason",    "Martin",  "19960725",  "20060725", 1234.56, "Toronto",  "O");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(2,"Alison",   "Mathews",  "19760321", "19860221", 6661.78, "Vancouver","O");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(3,"James",    "Smith",    "19781212", "19900315", 6544.78, "Vancouver","U");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(4,"Celia",    "Rice",     "19821024", "19990421", 2344.78, "Vancouver","U");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(5,"Robert",   "Black",    "19840115", "19980808", 2334.78, "Vancouver","Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(6,"Linda",    "Green",    "19870730", "19960104", 4322.78,"New York",  "N");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(7,"David",    "Larry",    "19901231", "19980212", 7897.78,"New York",  "N");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(8,"James",    "Cat",     "19960917",  "20020415", 1232.78,"Vancouver", "N");

Query OK, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | O | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | O | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | U | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | U | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | N | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | N | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | N | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql> mysql> delimiter $$ mysql> mysql> CREATE FUNCTION cust_status(in_status CHAR(1)) 

   ->      RETURNS VARCHAR(20)
   -> BEGIN
   ->      DECLARE long_status VARCHAR(20);
   ->
   ->      IF in_status = "O" THEN
   ->           SET long_status="Overdue";
   ->      ELSEIF in_status = "U" THEN
   ->           SET long_status="Up to date";
   ->      ELSEIF in_status = "N" THEN
   ->           SET long_status="New";
   ->      END IF;
   ->
   ->      RETURN(long_status);
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> mysql> delimiter ; mysql> mysql> SELECT cust_status(description) as Status, count(*) as Count 

   ->   FROM employee
   ->  GROUP BY description
   ->  ORDER BY cust_status(description);

+------------+-------+ | Status | Count | +------------+-------+ | NULL | 1 | | New | 3 | | Overdue | 2 | | Up to date | 2 | +------------+-------+ 4 rows in set, 1 warning (0.00 sec) mysql> mysql> drop function cust_status; Query OK, 0 rows affected (0.00 sec) mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.00 sec) mysql> 

       </source>


Use user-defined function in where clause

   <source lang="sql">

mysql> mysql> mysql> CREATE TABLE Employee( 

   ->     id            int,
   ->     first_name    VARCHAR(15),
   ->     last_name     VARCHAR(15),
   ->     start_date    DATE,
   ->     end_date      DATE,
   ->     salary        FLOAT(8,2),
   ->     city          VARCHAR(10),
   ->     description   VARCHAR(15)
   -> );

Query OK, 0 rows affected (0.01 sec) mysql> mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->              values (1,"Jason",    "Martin",  "19960725",  "20060725", 1234.56, "Toronto",  "Programmer");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(2,"Alison",   "Mathews",  "19760321", "19860221", 6661.78, "Vancouver","Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(3,"James",    "Smith",    "19781212", "19900315", 6544.78, "Vancouver","Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(4,"Celia",    "Rice",     "19821024", "19990421", 2344.78, "Vancouver","Manager");

Query OK, 1 row affected (0.01 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(5,"Robert",   "Black",    "19840115", "19980808", 2334.78, "Vancouver","Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(6,"Linda",    "Green",    "19870730", "19960104", 4322.78,"New York",  "Tester");

Query OK, 1 row affected (0.02 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(7,"David",    "Larry",    "19901231", "19980212", 7897.78,"New York",  "Manager");

Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description) 

   ->               values(8,"James",    "Cat",     "19960917",  "20020415", 1232.78,"Vancouver", "Tester");

Query OK, 1 row affected (0.00 sec) mysql> mysql> select * from Employee; +------+------------+-----------+------------+------------+---------+-----------+-------------+ | id | first_name | last_name | start_date | end_date | salary | city | description | +------+------------+-----------+------------+------------+---------+-----------+-------------+ | 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer | | 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester | | 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester | | 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager | | 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester | | 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester | | 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager | | 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester | +------+------------+-----------+------------+------------+---------+-----------+-------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql> mysql> delimiter $$ mysql> mysql> CREATE FUNCTION myFunction(in_rep_id INT) 

   ->      RETURNS INT
   ->      READS SQL DATA
   -> BEGIN
   ->      DECLARE customer_count INT;
   ->
   ->      SELECT COUNT(*)
   ->           INTO customer_count
   ->        FROM employee
   ->       WHERE id=in_rep_id;
   ->
   ->      RETURN(customer_count);
   ->
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> mysql> delimiter ; mysql> mysql> SELECT id,myFunction(id) 

   ->   FROM employee
   ->  WHERE myFunction(id)>0
   ->  ORDER BY myFunction(id) desc;

+------+----------------+ | id | myFunction(id) | +------+----------------+ | 1 | 1 | | 2 | 1 | | 3 | 1 | | 4 | 1 | | 5 | 1 | | 6 | 1 | | 7 | 1 | | 8 | 1 | +------+----------------+ 8 rows in set (0.01 sec) mysql> mysql> drop function myFunction; Query OK, 0 rows affected (0.00 sec) mysql> mysql> mysql> mysql> mysql> drop table Employee; Query OK, 0 rows affected (0.02 sec) mysql> 

       </source>


Using user-defined function in a select statement

   <source lang="sql">

mysql> delimiter $$ mysql> mysql> CREATE FUNCTION myFunction( 

   ->         in_title          VARCHAR(4),
   ->         in_gender         CHAR(1),
   ->         in_firstname      VARCHAR(20),
   ->         in_middle_initial CHAR(1),
   ->         in_surname        VARCHAR(20))
   ->
   ->   RETURNS VARCHAR(60)
   -> BEGIN
   ->   DECLARE l_title               VARCHAR(4);
   ->   DECLARE l_name_string         VARCHAR(60);
   ->
   ->   IF ISNULL(in_title)  THEN
   ->      IF in_gender="M" THEN
   ->         SET l_title="Mr";
   ->      ELSE
   ->         SET l_title="Ms";
   ->      END IF;
   ->   END IF;
   ->
   ->   IF ISNULL(in_middle_initial) THEN
   ->      SET l_name_string=l_title||" "||in_firstname||" "||in_surname;
   ->   ELSE
   ->      SET l_name_string=l_title||" "||in_firstname||" "||
   ->                           in_middle_initial||" "||in_surname;
   ->   END IF;
   ->
   ->   RETURN(l_name_string);
   -> END$$

Query OK, 0 rows affected (0.00 sec) mysql> mysql> delimiter ; mysql> mysql> select myFunction("Mrs","M","First","Middle","Last"); +-----------------------------------------------+ | myFunction("Mrs","M","First","Middle","Last") | +-----------------------------------------------+ | NULL | +-----------------------------------------------+ 1 row in set, 2 warnings (0.00 sec) mysql> mysql> mysql> select myFunction(null,"M","First","Middle","Last"); +----------------------------------------------+ | myFunction(null,"M","First","Middle","Last") | +----------------------------------------------+ | 0 | +----------------------------------------------+ 1 row in set, 2 warnings (0.02 sec) mysql> mysql> drop function myFunction; Query OK, 0 rows affected (0.00 sec) mysql> mysql> 

       </source>
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