Using user-defined function in a select statement : Introduction « Procedure Function « SQL / MySQL

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13. Procedure Function
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SQL / MySQL » Procedure Function » Introduction 
Using user-defined function in a select statement
 
mysql> delimiter $$
mysql>
mysql> CREATE FUNCTION myFunction(
    ->         in_title          VARCHAR(4),
    ->         in_gender         CHAR(1),
    ->         in_firstname      VARCHAR(20),
    ->         in_middle_initial CHAR(1),
    ->         in_surname        VARCHAR(20))
    ->
    ->   RETURNS VARCHAR(60)
    -> BEGIN
    ->   DECLARE l_title               VARCHAR(4);
    ->   DECLARE l_name_string         VARCHAR(60);
    ->
    ->   IF ISNULL(in_title)  THEN
    ->      IF in_gender='M' THEN
    ->         SET l_title='Mr';
    ->      ELSE
    ->         SET l_title='Ms';
    ->      END IF;
    ->   END IF;
    ->
    ->   IF ISNULL(in_middle_initialTHEN
    ->      SET l_name_string=l_title||' '||in_firstname||' '||in_surname;
    ->   ELSE
    ->      SET l_name_string=l_title||' '||in_firstname||' '||
    ->                           in_middle_initial||' '||in_surname;
    ->   END IF;
    ->
    ->   RETURN(l_name_string);
    -> END$$
Query OK, rows affected (0.00 sec)

mysql>
mysql> delimiter ;
mysql>
mysql> select myFunction('Mrs','M','First','Middle','Last');
+-----------------------------------------------+
| myFunction('Mrs','M','First','Middle','Last') |
+-----------------------------------------------+
| NULL                                          |
+-----------------------------------------------+
row in set, warnings (0.00 sec)

mysql>
mysql>
mysql> select myFunction(null,'M','First','Middle','Last');
+----------------------------------------------+
| myFunction(null,'M','First','Middle','Last') |
+----------------------------------------------+
0                                            |
+----------------------------------------------+
row in set, warnings (0.02 sec)

mysql>
mysql> drop function myFunction;
Query OK, rows affected (0.00 sec)

mysql>
mysql>

        
Related examples in the same category
1. Use user-defined function in a select statement to deal with data in a table
2. Use user-defined function in order by clause
3. Use user-defined function in where clause
4. Recursion
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