Set PK in Mysql database with autoincrement(string,int) - mysql

Question

I want to have a composite primarykey with (string,int) format where the string is a default value and int is set to autoincrement. Is it possible to achieve this. I need it in the below format
TC_01
TC_02
TC_03
.
.
.
so on

Answer 1

As the auto incremented value is identified just before insertion into the table, you should better depend on a before insert trigger on your table.
To set the concatenated string as in the form TC_002 etc, you need following steps in the trigger body.
Let us say if your str_field is defined as default 'TC', then
FOR EACH ROW BEGIN
SET NEW.str_field = concat( NEW.str_field, '_', NEW.auto_int_field );
END;
Note:
In case you have input a specific value, that is used for
concatenation.
In case if str_field allows null and you have not defined a default
value and you have not input any value for the same for insertion, the
concat( NEW.str_field, ... results a NULL.
You can define composite unique key on str_field and auto_int_field primary key field.
Constraint UK_CMP unique key ( str_field, auto_int_field )
EDIT:
when i use this trigger am getting str_field as TC_0 in all rows. But i should get TC_1,TC_2 etc.
You need an example like this:
mysql> drop table if exists cmp_pk;
Query OK, 0 rows affected (0.22 sec)
mysql> create table cmp_pk(
-> str varchar(10) not null unique default 'TC_',
-> id int not null auto_increment primary key,
-> constraint uk_cmp unique key( str, id )
-> );
Query OK, 0 rows affected (0.65 sec)
mysql>
mysql> drop trigger if exists bi_cmp_pk;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> delimiter //
mysql> create trigger bi_cmp_pk before insert on cmp_pk
-> for each row begin
-> SET #NEW_ID := ( SELECT AUTO_INCREMENT FROM INFORMATION_SCHEMA.TABLES
-> WHERE TABLE_NAME='cmp_pk' AND TABLE_SCHEMA=DATABASE() );
-> SET NEW.str = concat( NEW.str, #NEW_ID );
-> end;
-> //
Query OK, 0 rows affected (0.07 sec)
mysql> delimiter ;
mysql>
mysql> insert into cmp_pk values();
Query OK, 1 row affected (0.06 sec)
mysql> select * from cmp_pk;
+------+----+
| str | id |
+------+----+
| TC_1 | 1 |
+------+----+
1 row in set (0.00 sec)
mysql>
mysql> insert into cmp_pk values();
Query OK, 1 row affected (0.06 sec)
mysql> select * from cmp_pk;
+------+----+
| str | id |
+------+----+
| TC_1 | 1 |
| TC_2 | 2 |
+------+----+

Answer 2

DELIMITER $$
CREATE TRIGGER bi_cmp_pk
BEFORE INSERT ON cmp_pk
FOR EACH ROW BEGIN
SET #NEW_ID := ( SELECT last_insert_id()+1 from cmp_pk limit 1 );
SET NEW.str = concat( NEW.str, #NEW_ID );
end;
$$ DELIMITER ;
this trigger should solve your problem

Answer 3

Actually i dont know what actually you want but may this code will help you
CREATE TABLE tbl_name (
col1 varchar(255) DEFAULT 'TC_',
id INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (col1,id));