create table test1 (
id int not null auto_increment primary key,
a varchar(16), b varchar(16)
);
INSERT INTO test1 (a,b) VALUES ('a1','b3') ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), b='3';
The above line should insert an entry since the table is empty.
INSERT INTO test1 (a,b) VALUES ('a1','b3') ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), b='3';
Run the line again, it should replace b with "3" since a1, b3 already exist. But mysql adds another line for me. I have searched awhile and can not find a solution.
Latest update: Thanks for all your help. I figured one of the column must be unique.
Alter table test1 add unique (a)
solve the problem.
The ON DUPLICATE is only triggered if the column has a UNIQUE KEY. Try adding a UNIQUE INDEX on your table on the a or b columns and it should work as intended.
There is no duplicate key in your case. Only unique column in your table is primary key id
Try
INSERT INTO test1 (id,a,b) VALUES (1,'a1','b3') ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), b='3';
twice.
First line of documentation says.
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, an UPDATE of the old row is performed.
See the full documentation.
Related
CREATE TABLE IF NOT EXISTS students (
student_id INT,
name VARCHAR(24),
major VARCHAR(24),
PRIMARY KEY(student_id)
);
SELECT * FROM student;
INSERT INTO students VALUES(1,'Jack','Biology');
You're specifying the primary key (student_id) and from the error it already exists. You have a few options:
Don't specify the primary key. It should be set to autoincrement anyway, assuming that this is the primary table that students are entered into, and from the name of the table (students) it seems like it is. Then the query will be:
INSERT INTO students VALUES('Jack','Biology');
and then the table will autoincrement the primary key to the next pointer.
Use INSERT IGNORE. This will silently fail if you try to insert a student ID that already exists (or on any query that violates unique keys).
INSERT IGNORE INTO students VALUES(1, 'Jack','Biology');
This will not cause table changes, but it will also not cause an error that interrupts the script, and it will insert any rows that don't fail, say if you had multiple values inserted. The plain INSERT will fail for the entire list, not just the erroneous value.
Use ON DUPLICATE KEY UPDATE. This will update a list of values if it encounters a duplicate key.
INSERT INTO students VALUES(1, 'Jack','Biology')
ON DUPLICATE KEY UPDATE name = values(name), major = values(major);
In this case, you will change the values in the table that match the key. In this case, whichever student is student_id 1 will have its name and major updated to the supplied values. For instance, let's say that Jack changed his major to Chemistry. This would update student_id 1 to Jack, Chemistry and reflect his new major.
Use REPLACE INTO. I avoid this one. It is similar to ON DUPLICATE KEY UPDATE, but it removes the old entry and replaces it with a new one with a new ID. This can cause you problems with foreign keys, and also if you have a small primary key and you constantly replace into it, you can end up with a primary id that's bigger than the limits you set.
Well, your student_id is primary key, clearly that table is already exist with some data with student_id=1 hence you cannot insert another row with the same primary key value.
Hello I am using the "INSERT ON DUPLICATE KEY UPDATE" sql statement to update my database.
All was working fine since I always inserted an unique id like this:
INSERT INTO devices(uniqueId,name)
VALUES (4,'Printer')
ON DUPLICATE KEY UPDATE name = 'Central Printer';
But for now, I need to insert elements but I don't insert a unique id, I only insert or update the values like this:
INSERT INTO table (a,b,c,d,e,f,g)
VALUES (2,3,4,5,6,7,8)
ON DUPLICATE KEY
UPDATE a=a, b=b, c=c, d=d, e=e, f=f, g=g;
Have to say that an autoincrement primary key is generated always that I insert a row.
My problem is that now the inserted rows are duplicated since I don't insert the primary key or unique id explicitly within the sql statement.
What I am supposed to do?
For example, maybe I need to insert the primary key explicitly? I would like to work with this primary autoincremented key.
For recommendation from Gordon I am adding a sample case the you can see in the next image
Rows Output
In this case I add the first three rows, and then I try to update the three first rows again with different information.... Ok I am seeing the error... There is no key to compare to...... :$
Thanks for your answers,
If you want to prevent columns from being duplicated, then create a unique index or constraint on them. For instance:
create unique index unq_table_7 on table(a, b, c, d, e, f, g);
This will guarantee that the 7 columns -- in combination -- are unique.
I've been reading up on how to use MySQL insert on duplicate key to see if it will allow me to avoid Selecting a row, checking if it exists, and then either inserting or updating. As I've read the documentation however, there is one area that confuses me. This is what the documentation says:
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, an UPDATE of the old row is performed
The thing is, I don't want to know if this will work for my problem, because the 'condition' I have for not inserting a new one is the existence of a row that has two columns equal to a certain value, not necessarily that the primary key is the same. Right now the syntax I'm imagining is this, but I don't know if it will always insert instead of replace:
INSERT INTO attendance (event_id, user_id, status) VALUES(some_event_number, some_user_id, some_status) ON DUPLICATE KEY UPDATE status=1
The thing is, event_id and user_id aren't primary keys, but if a row in the table 'attendance' already has those columns with those values, I just want to update it. Otherwise I would like to insert it. Is this even possible with ON DUPLICATE? If not, what other method might I use?
The quote includes "a duplicate value in a UNIQUE index". So, your values do not need to be the primary key:
create unique index attendance_eventid_userid on attendance(event_id, user_id);
Presumably, you want to update the existing record because you don't want duplicates. If you want duplicates sometimes, but not for this particular insert, then you will need another method.
If I were you, I would make a primary key out of event_id and user_id. That will make this extremely easy with ON DUPLICATE.
SQLFiddle
create table attendance (
event_id int,
user_id int,
status varchar(100),
primary key(event_id, user_id)
);
Then with ease:
insert into attendance (event_id, user_id, status) values(some_event_number, some_user_id, some_status)
on duplicate key
update status = values(status);
Maybe you can try to write a trigger that checks if the pair (event_id, user_id) exists in the table before inserting, and if it exists just update it.
To the broader question of "Will INSERT ... ON DUPLICATE respect a UK even if the PK changes", the answer is yes: SQLFiddle
In this SQLFiddle I insert a new record, with a new PK id, but its values would violate the UK. It performs the ON DUPLICATE and the original PK id is preserved, but the non-UK ON DUPLICATE KEY UPDATE value changes.
I am trying to write a query to check if a record exists (based on couple of clause and not unique identifier) if such a search return records then I need to update all the found records if nothing found then I need to INSERT a record. Note that I can't use IF EXISTS because I am trying to make a query for a client side script and not a server side. So I came a cross the idea of INSERT INTO .... ON DUPLICATE KEY
Can I do this without knowing the row key identifier? So if I find a record where accountid = 17 and name = 'Mike' then update it to make the name 'Mike A' if there is no record with these 2 clause then insert a record.
This is an attempt that is giving me a syntax error
INSERT INTO test (name, accountid) VALUES ('Mike', 17)
ON DUPLICATE KEY
UPDATE test SET name='Mike A' WHERE name ='Mike' AND accountid = 17
Can this method handle what I am trying to do? If yes then can you please correct my syntax?
Thank you
The only way you can get this to work is if you have a primary key or unique constraint on the fields. From the documentation:
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, an
UPDATE of the old row is performed. For example, if column a is
declared as UNIQUE and contains the value 1, the following two
statements have identical effect:
create table test (name varchar(100), accountid int);
insert into test values ('Mike', 17);
alter table test add unique (name, accountid);
insert int test (name, accountid) values ('Mike', 17)
on duplicate key update name='Mike A';
SQL Fiddle Demo
Without the unique key, it will insert a duplicate record.
I have a table:
CREATE TABLE Students (studentId TEXT PRIMARY KEY, name TEXT);
I want to insert records into the table, if I insert a student twice I want
the second insert to override(update) the first record.
INSERT INTO Students (StudentId, name) VALUES ('123', 'Jones');
INSERT INTO Students (StudentId, name) VALUES ('123', 'Jonas');
What's the best way of doing this?
Try REPLACE:
REPLACE INTO Students (StudentId, name) VALUES ('123', 'Jonas');
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted.
You can also use the INSERT ... ON DUPLICATE KEY UPDATE syntax:
INSERT INTO Students
(StudentId, name)
VALUES ('123', 'Jones')
ON DUPLICATE KEY UPDATE
name = VALUES(name) ;
See this answer: insert-ignore-vs-insert-on-duplicate-key-update for differences between REPLACE, INSERT ... ON DUPLICATE KEY UPDATE and INSERT IGNORE.
But please, tell us that the studentId TEXT PRIMARY KEY is a typo. Do you really have a Primary Key that is TEXT datatype? The name (studentId) suggests that it could be a simple INT or INT AUTO_INCREMENT.
If you are using MySql - just use REPLACE instead of INSERT
I had a similar issue, but with a table that already had data in it, and no foreign keys, so my solution was very simple:
I added a new column called temp_id and made that a primary key, then afterwards deleted the old ID column, and then renamed the temp_id column to id.