I have 4 integer columns in my table. They are not required to be filled. So some of them may be filled, some not.
When they are not filled, MySQL adds 0 to that column. I tried to change the column default value to NULL and it told "Invalid default value".
Is there any way to get an empty row without having there zero?
"Is there any way to get empty row without having there the zero?"
To have NULL in the column by default use the following syntax in create table:
`column` int(10) unsigned DEFAULT NULL,
To alter the existing column:
ALTER TABLE table_name CHANGE COLUMN `column_name` `column_name` int(10) unsigned DEFAULT NULL;
If your columns are NULL'able then it should work just fine
mysql> CREATE TABLE Table1
-> (id int not null auto_increment primary key,
-> `col1` int, `col2` int, `col3` int, `col4` int);
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql> INSERT INTO Table1 (`col1`, `col2`, `col3`, `col4`)
-> VALUES (1, 1, 1, 1);
Query OK, 1 row affected (0.03 sec)
mysql>
mysql> INSERT INTO Table1 () VALUES();
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM table1;
+----+------+------+------+------+
| id | col1 | col2 | col3 | col4 |
+----+------+------+------+------+
| 1 | 1 | 1 | 1 | 1 |
| 2 | NULL | NULL | NULL | NULL |
+----+------+------+------+------+
2 rows in set (0.00 sec)
In that case you need to change your datatype into varchar and add default value NULL.
ALTER TABLE <table_name>
ALTER COLUMN <column_name1> <datatype1> <constraint1>
You have to alter your column to allow NULL values. This question has already been answered before:
How do I modify a MySQL column to allow NULL?
Related
How to receive results from mysql table where field value is NOT 0 or NULL? If I write condition field!=1, it gives nothing, but there are a lot of fields where field!=1. Why?
UPDATE:
CREATE TABLE `test` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`somevar` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `test` (`id`, `somevar`)
VALUES
(1,1),
(2,0),
(3,NULL),
(4,NULL),
(5,0);
This query
SELECT * FROM `test` WHERE `somevar`!=1
gives back only where somevar=0, but not NUL. how to echo all results where somevar!=1?
You can use NULL-safe equal to operator:
mysql> DROP TABLE IF EXISTS `test`;
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE IF NOT EXISTS `test` (
-> `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
-> `somevar` int(11) DEFAULT NULL,
-> PRIMARY KEY (`id`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO `test`
-> (`somevar`)
-> VALUES
-> (1), (0),
-> (NULL), (NULL),
-> (0);
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> SELECT `id`, `somevar`
-> FROM `test`
-> WHERE NOT `somevar` <=> 1;
+----+---------+
| id | somevar |
+----+---------+
| 2 | 0 |
| 3 | NULL |
| 4 | NULL |
| 5 | 0 |
+----+---------+
4 rows in set (0.00 sec)
See db-fiddle.
This has been answered many times on this site. NULL Is neither equal nor not equal to anything else. It cannot be compared in traditional ways. You have to ask for NULL values explicitly.
SELECT * FROM `test` WHERE `somevar`!=1 OR `somevar` IS NULL
You can use somevar IS NULL. For mysql NULL is unknown value, therefore NULL != 1 is NULL instead of true. For detailed information you can look at mysql documentation
SELECT * FROM `test` WHERE `somevar` IS NULL OR `somevar`!=1
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
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 |
+------+----+
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
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));
I have multiple databases with the same structure in which data is sometimes copied across. In order to maintain data integrity I am using two columns as the primary key. One is a database id, which links to a table with info about each database. The other is a table key. It is not unique because it may have multiple rows with this value being the same, but different values in the database_id column.
I am planning on making the two columns into a joint primary key. However I also want to set the table key to auto increment - but based on the database_id column.
EG, With this data:
table_id database_id other_columns
1 1
2 1
3 1
1 2
2 2
If I am adding data that includes the dabase_id of 1 then I want table_id to be automatically set to 4. If the dabase_id is entered as 2 then I want table_id to be automatically set to 3. etc.
What is the best way of achieving this in MySql.
if you are using myisam
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
For MyISAM and BDB tables you can
specify AUTO_INCREMENT on a secondary
column in a multiple-column index. In
this case, the generated value for the
AUTO_INCREMENT column is calculated as
MAX(auto_increment_column) + 1 WHERE
prefix=given-prefix. This is useful
when you want to put data into ordered
groups.
CREATE TABLE animals (
grp ENUM('fish','mammal','bird') NOT NULL,
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (grp,id)
) ENGINE=MyISAM;
INSERT INTO animals (grp,name) VALUES
('mammal','dog'),('mammal','cat'),
('bird','penguin'),('fish','lax'),('mammal','whale'),
('bird','ostrich');
SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
| bird | 2 | ostrich |
+--------+----+---------+
For your example:
mysql> CREATE TABLE mytable (
-> table_id MEDIUMINT NOT NULL AUTO_INCREMENT,
-> database_id MEDIUMINT NOT NULL,
-> other_column CHAR(30) NOT NULL,
-> PRIMARY KEY (database_id,table_id)
-> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.03 sec)
mysql> INSERT INTO mytable (database_id, other_column) VALUES
-> (1,'Foo'),(1,'Bar'),(2,'Baz'),(1,'Bam'),(2,'Zam'),(3,'Zoo');
Query OK, 6 rows affected (0.00 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM mytable ORDER BY database_id,table_id;
+----------+-------------+--------------+
| table_id | database_id | other_column |
+----------+-------------+--------------+
| 1 | 1 | Foo |
| 2 | 1 | Bar |
| 3 | 1 | Bam |
| 1 | 2 | Baz |
| 2 | 2 | Zam |
| 1 | 3 | Zoo |
+----------+-------------+--------------+
6 rows in set (0.00 sec)
Here's one approach when using innodb which will also be very performant due to the clustered composite index - only available with innodb...
http://dev.mysql.com/doc/refman/5.0/en/innodb-index-types.html
drop table if exists db;
create table db
(
db_id smallint unsigned not null auto_increment primary key,
next_table_id int unsigned not null default 0
)engine=innodb;
drop table if exists tables;
create table tables
(
db_id smallint unsigned not null,
table_id int unsigned not null default 0,
primary key (db_id, table_id) -- composite clustered index
)engine=innodb;
delimiter #
create trigger tables_before_ins_trig before insert on tables
for each row
begin
declare v_id int unsigned default 0;
select next_table_id + 1 into v_id from db where db_id = new.db_id;
set new.table_id = v_id;
update db set next_table_id = v_id where db_id = new.db_id;
end#
delimiter ;
insert into db (next_table_id) values (null),(null),(null);
insert into tables (db_id) values (1),(1),(2),(1),(3),(2);
select * from db;
select * from tables;
you can make the two column primary key unique and the auto-increment key primary.
The solution provided by DTing is excellent and working. But when tried the same in AWS Aurora, it didn't worked and complaining the below error.
Error Code: 1075. Incorrect table definition; there can be only one auto column and it must be defined as a key
Hence suggesting json based solution here.
CREATE TABLE DB_TABLE_XREF (
db VARCHAR(36) NOT NULL,
tables JSON,
PRIMARY KEY (db)
)
Have the first primary key outside, and second primary key inside the json and make second primary key value as auto_incr_sequence.
INSERT INTO `DB_TABLE_XREF`
(`db`, `tables`)
VALUES
('account_db', '{"user_info": 1, "seq" : 1}')
ON DUPLICATE KEY UPDATE `tables` =
JSON_SET(`tables`,
'$."user_info"',
IFNULL(`tables` -> '$."user_info"', `tables` -> '$."seq"' + 1),
'$."seq"',
IFNULL(`tables` -> '$."user_info"', `tables` -> '$."seq"' + 1)
);
And the output is like below
account_db {"user_info" : 1, "user_details" : 2, "seq" : 2}
product_db {"product1" : 1, "product2" : 2, "product3" : 3, "seq" : 3}
If your secondary keys are huge, and afraid of using json, then i would suggest to have stored procedure, to check for MAX(secondary_column) along with lock like below.
SELECT table_id INTO t_id FROM DB_TABLE_XREF WHERE database = db_name AND table = table_name;
IF t_id = 0 THEN
SELECT GET_LOCK(db_name, 10) INTO acq_lock;
-- CALL debug_msg(TRUE, "Acquiring lock");
IF acq_lock = 1 THEN
SELECT table_id INTO t_id FROM DB_TABLE_XREF WHERE database_id = db_name AND table = table_name;
-- double check lock
IF t_id = 0 THEN
SELECT IFNULL((SELECT MAX(table_id) FROM (SELECT table_id FROM DB_TABLE_XREF WHERE database = db_name) AS something), 0) + 1 into t_id;
INSERT INTO DB_TABLE_XREF VALUES (db_name, table_name, t_id);
END IF;
ELSE
-- CALL debug_msg(TRUE, "Failed to acquire lock");
END IF;
COMMIT;
I'm creating a stored function which should insert new row to table. In this table is also one unique column.
How can I check if everything goes well and row really was inserted?
How can I check exactly that it's this unique column found (for example - try to add duplicate value)?
You can check the LAST_INSERT_ID() function and INSERT IGNORE.
If the INSERT IGNORE was successful, you get the primary key returned. Let's create a table with an auto increment primary key and a unique key on a name.
use test
DROP TABLE IF EXISTS nametable;
CREATE TABLE nametable
(
id int not null auto_increment,
name varchar(20) not null,
primary key (id),
unique key (name)
);
DELIMITER $$
DROP FUNCTION IF EXISTS `test`.`InsertName` $$
CREATE FUNCTION `test`.`InsertName` (newname VARCHAR(20)) RETURNS INT
BEGIN
INSERT IGNORE INTO test.nametable (name) VALUES (newname);
RETURN LAST_INSERT_ID();
END $$
DELIMITER ;
SELECT InsertName('rolando');
SELECT InsertName('rolando');
SELECT InsertName('pamela');
SELECT InsertName('pamela');
SHOW CREATE TABLE test.nametable\G
SELECT * FROM test.nametable;
Here is the example being run:
mysql> use test
Database changed
mysql> DROP TABLE IF EXISTS nametable;
Query OK, 0 rows affected (0.04 sec)
mysql> CREATE TABLE nametable
-> (
-> id int not null auto_increment,
-> name varchar(20) not null,
-> primary key (id),
-> unique key (name)
-> );
Query OK, 0 rows affected (0.07 sec)
mysql> DELIMITER $$
mysql> DROP FUNCTION IF EXISTS `test`.`InsertName` $$
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE FUNCTION `test`.`InsertName` (newname VARCHAR(20)) RETURNS INT
-> BEGIN
-> INSERT IGNORE INTO test.nametable (name) VALUES (newname);
-> RETURN LAST_INSERT_ID();
-> END $$
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> SELECT InsertName('rolando');
+-----------------------+
| InsertName('rolando') |
+-----------------------+
| 1 |
+-----------------------+
1 row in set (0.03 sec)
mysql> SELECT InsertName('rolando');
+-----------------------+
| InsertName('rolando') |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (0.02 sec)
mysql> SELECT InsertName('pamela');
+----------------------+
| InsertName('pamela') |
+----------------------+
| 3 |
+----------------------+
1 row in set (0.02 sec)
mysql> SELECT InsertName('pamela');
+----------------------+
| InsertName('pamela') |
+----------------------+
| 0 |
+----------------------+
1 row in set (0.03 sec)
mysql> SHOW CREATE TABLE test.nametable\G
*************************** 1. row ***************************
Table: nametable
Create Table: CREATE TABLE `nametable` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> SELECT * FROM test.nametable;
+----+---------+
| id | name |
+----+---------+
| 3 | pamela |
| 1 | rolando |
+----+---------+
2 rows in set (0.00 sec)
mysql>
As shown in the preceding example, you can check the return value of the function. A nonzero return value means the INSERT IGNORE went well. A zero return value indicates a duplicate key without introducing an error number to the mysqld.
The drawback to this approach is that you cannot go back and use id 2 and 4 because of failed attempts to INSERT IGNORE in the event of a duplicate key.
Let's try another example with a different stored function setup using INSERT and without using LAST_INSERT_ID():
use test
DROP TABLE IF EXISTS nametable;
CREATE TABLE nametable
(
id int not null auto_increment,
name varchar(20) not null,
primary key (id),
unique key (name)
);
DELIMITER $$
DROP FUNCTION IF EXISTS `test`.`InsertName` $$
CREATE FUNCTION `test`.`InsertName` (newname VARCHAR(20)) RETURNS INT
BEGIN
DECLARE rv INT;
SELECT COUNT(1) INTO rv FROM test.nametable WHERE name = newname;
IF rv = 0 THEN
INSERT INTO test.nametable (name) VALUES (newname);
END IF;
RETURN rv;
END $$
DELIMITER ;
SELECT InsertName('rolando');
SELECT InsertName('rolando');
SELECT InsertName('pamela');
SELECT InsertName('pamela');
SHOW CREATE TABLE test.nametable\G
SELECT * FROM test.nametable;
Here is the result:
mysql> use test
Database changed
mysql> DROP TABLE IF EXISTS nametable;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> CREATE TABLE nametable
-> (
-> id int not null auto_increment,
-> name varchar(20) not null,
-> primary key (id),
-> unique key (name)
-> );
Query OK, 0 rows affected (0.10 sec)
mysql> DELIMITER $$
mysql> DROP FUNCTION IF EXISTS `test`.`InsertName` $$
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE FUNCTION `test`.`InsertName` (newname VARCHAR(20)) RETURNS INT
-> BEGIN
-> DECLARE rv INT;
-> SELECT COUNT(1) INTO rv FROM test.nametable WHERE name = newname;
-> IF rv = 0 THEN
-> INSERT INTO test.nametable (name) VALUES (newname);
-> END IF;
-> RETURN rv;
-> END $$
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> SELECT InsertName('rolando');
+-----------------------+
| InsertName('rolando') |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (0.04 sec)
mysql> SELECT InsertName('rolando');
+-----------------------+
| InsertName('rolando') |
+-----------------------+
| 1 |
+-----------------------+
1 row in set (0.00 sec)
mysql> SELECT InsertName('pamela');
+----------------------+
| InsertName('pamela') |
+----------------------+
| 0 |
+----------------------+
1 row in set (0.03 sec)
mysql> SELECT InsertName('pamela');
+----------------------+
| InsertName('pamela') |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)
mysql> SHOW CREATE TABLE test.nametable\G
*************************** 1. row ***************************
Table: nametable
Create Table: CREATE TABLE `nametable` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> SELECT * FROM test.nametable;
+----+---------+
| id | name |
+----+---------+
| 2 | pamela |
| 1 | rolando |
+----+---------+
2 rows in set (0.00 sec)
mysql>
In this example, the stored function returns 0 if the INSERT was OK, and returns 1 with a duplicate key on the name. The advantage? No wasted id numbers for auto_increment. The disadvantage? Doing a SELECT statement each time to check for the name already being present in the table.
You have a choice as to which way you want to handle duplicate keys. The first method lets mysqld handle the condition of the INSERT IGNORE. The second method has the stored function checking for the duplicate key first before the INSERT.
Stored Procedures are "all-or-nothing"
Therefore, if you include an INSERT in the sproc, and that INSERT fails on a duplicate key error, the entire sproc will be rolled back.
If the sproc executes without error, you can be confident that the INSERT did not have an error. Now, this does not mean the INSERT actually happens just because the sproc completes, just that there were no errors.... for example, if you had some WHERE clause which excludes the INSERT but doesn't throw an error then there may be some ambiguity.
I have multiple databases with the same structure in which data is sometimes copied across. In order to maintain data integrity I am using two columns as the primary key. One is a database id, which links to a table with info about each database. The other is a table key. It is not unique because it may have multiple rows with this value being the same, but different values in the database_id column.
I am planning on making the two columns into a joint primary key. However I also want to set the table key to auto increment - but based on the database_id column.
EG, With this data:
table_id database_id other_columns
1 1
2 1
3 1
1 2
2 2
If I am adding data that includes the dabase_id of 1 then I want table_id to be automatically set to 4. If the dabase_id is entered as 2 then I want table_id to be automatically set to 3. etc.
What is the best way of achieving this in MySql.
if you are using myisam
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
For MyISAM and BDB tables you can
specify AUTO_INCREMENT on a secondary
column in a multiple-column index. In
this case, the generated value for the
AUTO_INCREMENT column is calculated as
MAX(auto_increment_column) + 1 WHERE
prefix=given-prefix. This is useful
when you want to put data into ordered
groups.
CREATE TABLE animals (
grp ENUM('fish','mammal','bird') NOT NULL,
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (grp,id)
) ENGINE=MyISAM;
INSERT INTO animals (grp,name) VALUES
('mammal','dog'),('mammal','cat'),
('bird','penguin'),('fish','lax'),('mammal','whale'),
('bird','ostrich');
SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
| bird | 2 | ostrich |
+--------+----+---------+
For your example:
mysql> CREATE TABLE mytable (
-> table_id MEDIUMINT NOT NULL AUTO_INCREMENT,
-> database_id MEDIUMINT NOT NULL,
-> other_column CHAR(30) NOT NULL,
-> PRIMARY KEY (database_id,table_id)
-> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.03 sec)
mysql> INSERT INTO mytable (database_id, other_column) VALUES
-> (1,'Foo'),(1,'Bar'),(2,'Baz'),(1,'Bam'),(2,'Zam'),(3,'Zoo');
Query OK, 6 rows affected (0.00 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM mytable ORDER BY database_id,table_id;
+----------+-------------+--------------+
| table_id | database_id | other_column |
+----------+-------------+--------------+
| 1 | 1 | Foo |
| 2 | 1 | Bar |
| 3 | 1 | Bam |
| 1 | 2 | Baz |
| 2 | 2 | Zam |
| 1 | 3 | Zoo |
+----------+-------------+--------------+
6 rows in set (0.00 sec)
Here's one approach when using innodb which will also be very performant due to the clustered composite index - only available with innodb...
http://dev.mysql.com/doc/refman/5.0/en/innodb-index-types.html
drop table if exists db;
create table db
(
db_id smallint unsigned not null auto_increment primary key,
next_table_id int unsigned not null default 0
)engine=innodb;
drop table if exists tables;
create table tables
(
db_id smallint unsigned not null,
table_id int unsigned not null default 0,
primary key (db_id, table_id) -- composite clustered index
)engine=innodb;
delimiter #
create trigger tables_before_ins_trig before insert on tables
for each row
begin
declare v_id int unsigned default 0;
select next_table_id + 1 into v_id from db where db_id = new.db_id;
set new.table_id = v_id;
update db set next_table_id = v_id where db_id = new.db_id;
end#
delimiter ;
insert into db (next_table_id) values (null),(null),(null);
insert into tables (db_id) values (1),(1),(2),(1),(3),(2);
select * from db;
select * from tables;
you can make the two column primary key unique and the auto-increment key primary.
The solution provided by DTing is excellent and working. But when tried the same in AWS Aurora, it didn't worked and complaining the below error.
Error Code: 1075. Incorrect table definition; there can be only one auto column and it must be defined as a key
Hence suggesting json based solution here.
CREATE TABLE DB_TABLE_XREF (
db VARCHAR(36) NOT NULL,
tables JSON,
PRIMARY KEY (db)
)
Have the first primary key outside, and second primary key inside the json and make second primary key value as auto_incr_sequence.
INSERT INTO `DB_TABLE_XREF`
(`db`, `tables`)
VALUES
('account_db', '{"user_info": 1, "seq" : 1}')
ON DUPLICATE KEY UPDATE `tables` =
JSON_SET(`tables`,
'$."user_info"',
IFNULL(`tables` -> '$."user_info"', `tables` -> '$."seq"' + 1),
'$."seq"',
IFNULL(`tables` -> '$."user_info"', `tables` -> '$."seq"' + 1)
);
And the output is like below
account_db {"user_info" : 1, "user_details" : 2, "seq" : 2}
product_db {"product1" : 1, "product2" : 2, "product3" : 3, "seq" : 3}
If your secondary keys are huge, and afraid of using json, then i would suggest to have stored procedure, to check for MAX(secondary_column) along with lock like below.
SELECT table_id INTO t_id FROM DB_TABLE_XREF WHERE database = db_name AND table = table_name;
IF t_id = 0 THEN
SELECT GET_LOCK(db_name, 10) INTO acq_lock;
-- CALL debug_msg(TRUE, "Acquiring lock");
IF acq_lock = 1 THEN
SELECT table_id INTO t_id FROM DB_TABLE_XREF WHERE database_id = db_name AND table = table_name;
-- double check lock
IF t_id = 0 THEN
SELECT IFNULL((SELECT MAX(table_id) FROM (SELECT table_id FROM DB_TABLE_XREF WHERE database = db_name) AS something), 0) + 1 into t_id;
INSERT INTO DB_TABLE_XREF VALUES (db_name, table_name, t_id);
END IF;
ELSE
-- CALL debug_msg(TRUE, "Failed to acquire lock");
END IF;
COMMIT;