MySQL - INSERT without duplicating rows (without informing the PK) - mysql

I have to insert a few values into a mysql table, but only if there are no other (almost) equal rows, for example:
TABLE T
KEY | COL1 | COL2
1 | abc | 123
2 | def | 456
The KEY column uses auto increment, and I don't inform it on the statement, like this:
INSERT INTO T (COL1, COL2) VALUES (abc, 123)
The statement above have the same values as the first row. How can I inform mysql that I don't want to insert if the row is a duplicate like that?
I googled for some solutions and found INSERT IGNORE, ..ON DUPLICATE KEY UPDATE and REPLACE in which I would have to inform the PK, but I don't know it (without using a extra query).


you can do like...
> INSERT INTO memos(id,text)
> SELECT 5, 'text to insert'
> WHERE NOT EXISTS(SELECT 1 FROM memos WHERE id = 5 AND text = 'text to insert');


ON DUPLICATE KEY and INSERT IGNORE will work with any unique index, not just the primary key. So you can add a unique index for these columns:
ALTER TABLE T
ADD UNIQUE INDEX (col1, col2);
Making it a multi-column index means that the combination has to be unique, even though each column can be duplicated individually.


if not exists(select * from t where col1 = "abc" and col2 ="123")then
insert into t (col1,col2) values("abc",123 );
end if;

Related

MySQL unique index on VARCHAR column (but only if longer than x characters) [duplicate]

I am using mysql db. I know postgresql and SQL server supports partial Indexing. In my case I want to do something like this:
CREATE UNIQUE INDEX myIndex ON myTable (myColumn) where myColumn <> 'myText'
I want to create a unique constraint but it should allow duplicates if it is a particular text.
I couldn't find a direct way to do this in mysql. But, is there a workaround to achieve it?

Filtered indexes could be emulated with function indexes and CASE expression(MySQL 8.0.13 and newer):
CREATE TABLE t(id INT PRIMARY KEY, myColumn VARCHAR(100));
-- NULL are not taken into account with `UNIQUE` indexes
CREATE UNIQUE INDEX myIndex ON t((CASE WHEN myColumn <> 'myText' THEN myColumn END));
-- inserting excluded value twice
INSERT INTO t(id, myColumn) VALUES(1, 'myText'), (2, 'myText');
-- trying to insert different value than excluded twice
INSERT INTO t(id, myColumn) VALUES(3, 'aaaaa');
INSERT INTO t(id, myColumn) VALUES(4, 'aaaaa');
-- Duplicate entry 'aaaaa' for key 'myIndex'
SELECT * FROM t;
db<>fiddle demo
Output:
+-----+----------+
| id | myColumn |
+-----+----------+
| 1 | myText |
| 2 | myText |
| 3 | aaaaa |
+-----+----------+

I suppose there is only one way to achieve it. You can add another column to your table, create index on it and create trigger or do insert/update inside your stored procedures to fill this column using following condition:
if value = 'myText' then put null
otherwise put value
Hope it helps

Insert or Update with mysql if same two column

I have a table to store client's answers.I want to use one mysql query to insert or update this table.
My Table name : questionform_answer
and columns > ClientID QuestionID OptionID
Each client can only have one same question id.For example
ClientID QuestionID OptionID
1 1 1
1 2 5
2 1 3
I want to update OptionID if already exist ClientID and QuestionID.I don't want to use select query so taking so time.
I tried
ON KEY UPDATE
Replace Into
But I could not.
I use php so I tried first update query and if mysqli return fail insert row but it is also slow.
MY insert and update code :
Insert Into questionform_answer (ClientID,QuestionID,OptionID) values
('$ClientID','$soruid','$cevapid')
Update questionform_answer set OptionID='$cevapid' where
ClientID='$ClientID' and QuestionID='$soruid'

One way around this is to add a unique key over (ClientID, QuestionID) and use an INSERT ... ON DUPLICATE KEY UPDATE query:
ALTER TABLE table1
ADD UNIQUE INDEX (ClientID, QuestionID);
INSERT INTO table1
VALUES (1, 1, 4)
ON DUPLICATE KEY UPDATE
OptionID = VALUES(OptionID)
Demo on dbfiddle

First of all, you should use prepared statements to avoid SQL injections.
If you have a unique key on (ClientID,QuestionID), you can do INSERT INTO ... ON DUPLICATE KEY like this:
INSERT INTO questionform_answer (ClientID,QuestionID,OptionID)
values ('$ClientID','$soruid','$cevapid')
on duplicate key update OptionID='$cevapid'

MySQL insert on duplicate update for non-PRIMARY key

I am little confused with insert on duplicate update query.
I have MySQL table with structure like this:
record_id (PRIMARY, UNIQUE)
person_id (UNIQUE)
some_text
some_other_text
I want to update some_text and some_other_text values for person if it's id exists in my table.person or insert new record in this table otherwise. How it can be done if person_id is not PRIMARY?

You need a query that check if exists any row with you record_id (or person_id). If exists update it, else insert new row
IF EXISTS (SELECT * FROM table.person WHERE record_id='SomeValue')
UPDATE table.person
SET some_text='new_some_text', some_other_text='some_other_text'
WHERE record_id='old_record_id'
ELSE
INSERT INTO table.person (record_id, person_id, some_text, some_other_text)
VALUES ('new_record_id', 'new_person_id', 'new_some_text', 'new_some_other_text')
Another better approach is
UPDATE table.person SET (...) WHERE person_id='SomeValue'
IF ROW_COUNT()=0
INSERT INTO table.person (...) VALUES (...)

Your question is very valid. This is a very common requirement. And most people get it wrong, due to what MySQL offers.
The requirement: Insert unless the PRIMARY key exists, otherwise update.
The common approach: ON DUPLICATE KEY UPDATE
The result of that approach, disturbingly: Insert unless the PRIMARY or any UNIQUE key exists, otherwise update!
What can go horribly wrong with ON DUPLICATE KEY UPDATE? You insert a supposedly new record, with a new PRIMARY key value (say a UUID), but you happen to have a duplicate value for its UNIQUE key.
What you want is a proper exception, indicating that you are trying to insert a duplicate into a UNIQUE column.
But what you get is an unwanted UPDATE! MySQL will take the conflicting record and start overwriting its values. If this happens unintentionally, you have mutilated an old record, and any incoming references to the old record are now referencing the new record. And since you probably won't tell the query to update the PRIMARY column, your new UUID is nowhere to be found. If you ever encounter this data, it will probably make no sense and you will have no idea where it came from.
We need a solution to actually insert unless the PRIMARY key exists, otherwise update.
We will use a query that consists of two statements:
Update where the PRIMARY key value matches (affects 0 or 1 rows).
Insert if the PRIMARY key value does not exist (inserts 1 or 0 rows).
This is the query:
UPDATE my_table SET
unique_name = 'one', update_datetime = NOW()
WHERE id = 1;
INSERT INTO my_table
SELECT 1, 'one', NOW()
FROM my_table
WHERE id = 1
HAVING COUNT(*) = 0;
Only one of these queries will have an effect. The UPDATE is easy. As for the INSERT: WHERE id = 1 results in a row if the id exists, or no row if it does not. HAVING COUNT(*) = 0 inverts that, resulting in a row if the id is new, or no row if it already exists.
I have explored other variants of the same idea, such as with a LEFT JOIN and WHERE, but they all looked more convoluted. Improvements are welcome.

13.2.5.3 INSERT ... ON DUPLICATE KEY UPDATE Syntax
If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that
would cause a duplicate value in a UNIQUE index or PRIMARY KEY, MySQL
performs an UPDATE of the old row.
Example:
DELIMITER //
DROP PROCEDURE IF EXISTS `sp_upsert`//
DROP TABLE IF EXISTS `table_test`//
CREATE TABLE `table_test` (
`record_id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`person_id` INT UNSIGNED NOT NULL,
`some_text` VARCHAR(50),
`some_other_text` VARCHAR(50),
UNIQUE KEY `record_id_index` (`record_id`),
UNIQUE KEY `person_id_index` (`person_id`)
)//
INSERT INTO `table_test`
(`person_id`, `some_text`, `some_other_text`)
VALUES
(1, 'AAA', 'XXX'),
(2, 'BBB', 'YYY'),
(3, 'CCC', 'ZZZ')//
CREATE PROCEDURE `sp_upsert`(
`p_person_id` INT UNSIGNED,
`p_some_text` VARCHAR(50),
`p_some_other_text` VARCHAR(50)
)
BEGIN
INSERT INTO `table_test`
(`person_id`, `some_text`, `some_other_text`)
VALUES
(`p_person_id`, `p_some_text`, `p_some_other_text`)
ON DUPLICATE KEY UPDATE `some_text` = `p_some_text`,
`some_other_text` = `p_some_other_text`;
END//
DELIMITER ;
mysql> CALL `sp_upsert`(1, 'update_text_0', 'update_text_1');
Query OK, 2 rows affected (0.00 sec)
mysql> SELECT
-> `record_id`,
-> `person_id`,
-> `some_text`,
-> `some_other_text`
-> FROM
-> `table_test`;
+-----------+-----------+---------------+-----------------+
| record_id | person_id | some_text | some_other_text |
+-----------+-----------+---------------+-----------------+
| 1 | 1 | update_text_0 | update_text_1 |
| 2 | 2 | BBB | YYY |
| 3 | 3 | CCC | ZZZ |
+-----------+-----------+---------------+-----------------+
3 rows in set (0.00 sec)
mysql> CALL `sp_upsert`(4, 'new_text_0', 'new_text_1');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT
-> `record_id`,
-> `person_id`,
-> `some_text`,
-> `some_other_text`
-> FROM
-> `table_test`;
+-----------+-----------+---------------+-----------------+
| record_id | person_id | some_text | some_other_text |
+-----------+-----------+---------------+-----------------+
| 1 | 1 | update_text_0 | update_text_1 |
| 2 | 2 | BBB | YYY |
| 3 | 3 | CCC | ZZZ |
| 5 | 4 | new_text_0 | new_text_1 |
+-----------+-----------+---------------+-----------------+
4 rows in set (0.00 sec)
SQL Fiddle demo

How about my approach?
Let's say you have one table with a autoincrement id and three text-columns. You want to insert/update the value of column3 with the values in column1 and column2 being a (non unique) key.
I use this query (without explicitly locking the table):
insert into myTable (id, col1, col2, col3)
select tmp.id, 'col1data', 'col2data', 'col3data' from
(select id from myTable where col1 = 'col1data' and col2 = 'col2data' union select null as id limit 1) tmp
on duplicate key update col3 = values(col3)
Anything wrong with that? For me it works the way I want.

A flexible solution should retain the atomicity offered by INSERT ... ON DUPLICATE KEY UPDATE and work regardless of if it's autocommit=true and not depend on a transaction with an isolation level of REPEATABLE READ or greater.
Any solution performing check-then-act across multiple statements would not satisfy this.
Here are the options:
If there tends to be more inserts than updates:
INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...);
IF <duplicate entry for primary key error>
UPDATE table SET some_text = ..., some_other_text = ... WHERE record_id = ...;
IF affected-rows = 0
-- retry from INSERT OR ignore this conflict and defer to the other session
If there tends to be more updates than inserts:
UPDATE table SET some_text = ..., some_other_text = ... WHERE record_id = ...;
IF affected-rows = 0
INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...);
IF <duplicate entry for primary key error>
-- retry from UPDATE OR ignore this conflict and defer to the other session
If you don't mind a bit of ugliness, you can actually use INSERT ... ON DUPLICATE KEY UPDATE and do this in a single statement:
INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...)
ON DUPLICATE KEY UPDATE
some_text = if(record_id = VALUES(record_id), VALUES(some_text), some_text),
some_other_text = if(record_id = VALUES(record_id), VALUES(some_other_text), some_other_text)
IF affected-rows = 0
-- handle this as a unique check constraint violation
Note: affected-rows in these examples mean affected rows and not found rows. The two can be confused because a single parameter switches which of these values the client is returned.
Also note, if some_text and some_other_text are not actually modified (and the record is not otherwise changed) when you perform the update, those checks on affected-rows = 0 will misfire.

I came across this post because I needed what's written in the title, and I found a pretty handy solution, but no one mentioned it here, so I thought of pasting it here. Note that this solution is very handy if you're initiating your database tables. In this case, when you create your corresponding table, define your primary key etc. as usual, and for the combination of columns you want to be unique, simply add
UNIQUE(column_name1,column_name2,...)
at the end of your CREATE TABLE statement, for any combination of the specified columns you want to be unique. Like this, according to this page here, "MySQL uses the combination of values in both column column_name1 and column_name2 to evaluate the uniqueness", and reports an error if you try to make an insert which already has the combination of values for column_name1 and column_name2 you provide in your insert. Combining this way of creating a database table with the corresponding INSERT ON DUPLICATE KEY syntax appeared to be the most suitable solution for me. Just need to think of it carefully before you actually start using your table; when setting up your database tables.

For anyone else, like me, who is a DB noob....the above things didn't work for me. I have a primary key and a unique key... And I wanted to insert if unique key didn't exist. After a LOT of Stack Overflow and Google searching, I found not many results for this... but I did find a site that gave me a working answer: https://thispointer.com/insert-record-if-not-exists-in-mysql/
And for ease of reading here is my answer from that site:
INSERT INTO table (unique_key_column_name)
SELECT * FROM (SELECT 'unique_value' AS unique_key_column_name) AS temp
WHERE NOT EXISTS (
SELECT unique_key_column_name FROM table
WHERE unique_key_column_name = 'unique_value'
) LIMIT 1;
Please also note the ' marks are wrapped around for me because I use string in this case.

Mysql on duplicate key replace all

I have a table T1:
Col1 | Col2
-------------
a | 2
b | 3
If Col1 is unique and Col2 is not then I can run the query:
INSERT INTO T1 (Col1, Col2)
VALUES (b,2)
ON DUPLICATE KEY UPDATE
Col2=VALUES(Col2);
and the table now looks like this:
Col1 | Col2
-------------
a | 2
b | 2
If Col1 and Col2 are both unique I would like to run a single query:
INSERT INTO T1 (Col1, Col2)
VALUES (b,2)
ON DUPLICATE KEY -- REPLACE ALL INSTANCES ?
Col1 = VALUES(Col1), Col2=VALUES(Col2);
which results in this:
Col1 | Col2
-------------
b | 2
So the key "b" is now associated with the key "2", replacing both "a"'s association and "b"'s previous association.
Is there a mysql query or extension that can accomplish this? (Clearly this can be done with multiple queries, I'm looking for an analogue of the ON DUPLICATE extension for this use case.)

After looking around for a while, I'm pretty certain that this cannot be done. There is no mention of anything other than UPDATE or IGNORE for ON DUPLICATE KEY in the manual. The requested action is tantamount to doing a DELETE inside an UPDATE statement. (Which you cannot do).
The following code performs the task, I don't like having to wrap it in a transaction but it is the only way to do it at the moment.
START TRANSACTION;
DELETE FROM t1 WHERE Col2 = 2 AND Col1 <> "b"; -- Without checking Col1 the row will be replaced instead of updated if the entry ("b",2) already exists
INSERT INTO t1 (Col1, Col2)
VALUES("b",2)
ON DUPLICATE KEY UPDATE
Col2 = VALUES(Col2);
COMMIT;

Workaround in mysql for partial Index or filtered Index?

I am using mysql db. I know postgresql and SQL server supports partial Indexing. In my case I want to do something like this:
CREATE UNIQUE INDEX myIndex ON myTable (myColumn) where myColumn <> 'myText'
I want to create a unique constraint but it should allow duplicates if it is a particular text.
I couldn't find a direct way to do this in mysql. But, is there a workaround to achieve it?

Filtered indexes could be emulated with function indexes and CASE expression(MySQL 8.0.13 and newer):
CREATE TABLE t(id INT PRIMARY KEY, myColumn VARCHAR(100));
-- NULL are not taken into account with `UNIQUE` indexes
CREATE UNIQUE INDEX myIndex ON t((CASE WHEN myColumn <> 'myText' THEN myColumn END));
-- inserting excluded value twice
INSERT INTO t(id, myColumn) VALUES(1, 'myText'), (2, 'myText');
-- trying to insert different value than excluded twice
INSERT INTO t(id, myColumn) VALUES(3, 'aaaaa');
INSERT INTO t(id, myColumn) VALUES(4, 'aaaaa');
-- Duplicate entry 'aaaaa' for key 'myIndex'
SELECT * FROM t;
db<>fiddle demo
Output:
+-----+----------+
| id | myColumn |
+-----+----------+
| 1 | myText |
| 2 | myText |
| 3 | aaaaa |
+-----+----------+

I suppose there is only one way to achieve it. You can add another column to your table, create index on it and create trigger or do insert/update inside your stored procedures to fill this column using following condition:
if value = 'myText' then put null
otherwise put value
Hope it helps