Create if an entry if it doesn't exist, otherwise update? - mysql

Kinda strange to put it into words that short, heh.
Anyway, what I want is basically to update an entry in a table if it does exist, otherwise to create a new one filling it with the same data.
I know that's easy, but I'm relatively new to MySQL in terms of how much I've used it :P

A lot of developers still execute a query to check if a field is present in a table and then execute an insert or update query according to the result of the first query.
Try using the ON DUPLICATE KEY syntax, this is a lot faster and better then executing 2 queries. More info can be found here
INSERT INTO table (a,b,c) VALUES (4,5,6)
ON DUPLICATE KEY UPDATE c=9;
if you want to keep the same value for c you can do an update with the same value
INSERT INTO table (a,b,c) VALUES (4,5,6)
ON DUPLICATE KEY UPDATE c=6;
the difference between 'replace' and 'on duplicate key':
replace: inserts, or deletes and inserts
on duplicate key: inserts or updates
if your table doesn't have a primary key or unique key, the replace doesn't make any sense.
You can also use the VALUES function to avoid having to specify the actual values twice. E.g. instead of
INSERT INTO table (a,b,c) VALUES (4,5,6) ON DUPLICATE KEY UPDATE c=6;
you can use
INSERT INTO table (a,b,c) VALUES (4,5,6) ON DUPLICATE KEY UPDATE c=VALUES(c);
Where VALUES(c) will evaluate to the value specified prevously (6).

Use 'REPLACE INTO':
REPLACE INTO table SET id = 42, foo = 'bar';
See more in the MySQL documentation

As the others have said, REPLACE is the way to go. Just be careful using it though, since it actually does a DELETE and INSERT on the table. This is fine most of the time, but if you have foreign keys with constraints like ON DELETE CASCADE, it can cause some big problems.

Look up REPLACE in the MySQL manual.
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. See Section 12.2.5, “INSERT
Syntax”.
REPLACE is a MySQL extension to the
SQL standard. It either inserts, or
deletes and inserts. For another MySQL
extension to standard SQL — that
either inserts or updates — see
Section 12.2.5.3, “INSERT ... ON
DUPLICATE KEY UPDATE Syntax”.
If you have the following INSERT query:
INSERT INTO table (id, field1, field2) VALUES (1, 23, 24)
This is the REPLACE query you should run:
REPLACE INTO table (id, field1, field2) VALUES (1, 23, 24)

Related

select and insert if value missing without duplicating primary keys [duplicate]

Since IF EXISTS isn't supported by MySQL I am struggling to think of the syntax for doing something like the following pseudo in MySQL:
IF ((select count(*) from table where col1='var1' AND col2='var2' AND col3='var3' AND col4='var4' AND col5='var5')>0) then
combination of vars exist in record - do a thing;
ELSE
combination of vars does not exist in record - insert record;
END IF;
I should have thought CASE would suit this but for life of me I'm unable to think of the correct syntax. I'd use unique indexes but every one of the columns needs to allow duplicates, it's only a matching combination of all the columns that needs to be unique, not the fields themselves.
I'm told using a composite key across all the columns would avoid duplicate inserts but from what I gather I need to use a different insert then.
Short version: In MySQL, how do I insert new row only if an exact specified match of columns is not found in an existing row.
Any advice or suggestions would be greatly appreciated.
Create a composite unique index. This will allow any number of duplicates in the individual fields, but the combination needs to be unique.
CREATE UNIQUE INDEX ix_uq ON test (field1, field2, field3);
...and use INSERT IGNORE to insert if the unique index is not violated. If it is, just ignore the insert.
INSERT IGNORE INTO test (field1,field2,field3) VALUES (1,1,1);
An SQLfiddle for testing.
If you want to insert unless there's a duplicate, and update if there is, you can also use INSERT INTO ... ON DUPLICATE KEY UPDATE;
INSERT INTO test (field1, field2, field3) VALUES (1,1,1)
ON DUPLICATE KEY UPDATE field4=field4+1;
Another SQLfiddle.

MySQL: Insert multiple values if they don't exist, but need a multiple column check

I have a simpe query like so:
INSERT INTO myTable (col1, col2) VALUES
(1,2),
(1,3),
(2,2)
I need to do a check that no duplicate values have been added BUT the check needs to happen across both column: if a value exists in col1 AND col2 then I don't want to insert. If the value exists only in one of those columns but not both then then insert should go through..
In other words let's say we have the following table:
+-------------------------+
|____col1____|___col2_____|
| 1 | 2 |
| 1 | 3 |
|______2_____|_____2______|
Inserting values like (2,3) and (1,1) would be allowed, but (1,3) would not be allowed.
Is it possible to do a WHERE NOT EXISTS check a single time? I may need to insert 1000 values at one time and I'm not sure whether doing a WHERE check on every single insert row would be efficient.
EDIT:
To add to the question - if there's a duplicate value across both columns, I'd like the query to ignore this specific row and continue onto inserting other values rather than throwing an error.
What you might want to use is either a primary key or a unique index across those columns. Afterwards, you can use either replace into or just insert ignore:
create table myTable
(
a int,
b int,
primary key (a,b)
);
-- Variant 1
replace into myTable(a,b) values (1, 2);
-- Variant 2
insert ignore into myTable(a,b) values (1,2);
See Insert Ignore and Replace Into
Using the latter variant has the advantage that you don't change any record if it already exists (thus no need to rebuild any index) and would best match your needs regarding your question.
If, however, there are other columns that need to be updated when inserting a record violating a unique constraint, you can either use replace into or insert into ... on duplicate key update.
Replace into will perform a real deletion prior to inserting a new record, whereas insert into ... on duplicate key update will perform an update instead. Although one might think that the result will be same, so why is there a statement for both operations, the answer can be found in the side-effects:
Replace into will delete the old record before inserting the new one. This causes the index to be updated twice, delete and insert triggers get executed (if defined) and, most important, if you have a foreign key constraint (with on delete restrict or on delete cascade) defined, your constraint will behave exactly the same way as if you deleted the record manually and inserted the new version later on. This means: Either your operation fails because the restriction is in place or the delete operation gets cascaded to the target table (i.e. deleting related records there, although you just changed some column data).
On the other hand, when using on duplicate key update, update triggers will get fired, the indexes on changed columns will be rewritten once and, if a foreign key is defined on update cascade for one of the columns being changed, this operation is performed as well.
To answer your question in the comments, as stated in the manual:
If you use the IGNORE modifier, errors that occur while executing the INSERT statement are ignored. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row is discarded and no error occurs. Ignored errors may generate warnings instead, although duplicate-key errors do not.
So, all violations are treated as warnings rather than errors, causing the insert to complete. Otherwise, the insert would be applied partially (except when using transactions). Violations of duplicate key, however, do not even produce such a warning. Nonetheless, all records violating any constraint won't get inserted at all, but ignore will ensure all valid records get inserted (given that there is no system failure or out-of-memory condition).

insert on duplicate key update

I would like to use "insert on duplicate key update" in a query to either insert a new row if it does not exist or update a row if it does. What I can not seem to figure out is how to use this if I do not have the unique id (because the row has not yet been created, and this ID will be autoincremented upon insert)
insert into foodchoices (unique,notunique) values (Idonthavethis,'test')
on duplicate key update notunique = 'stuff';
Now, in this example above, where it says "Idonthavethis", I do not have any unique value for this field, because it has not yet been inserted as a row. However, I do expect that this inserts somehow, I just dont know how. I expect it to act like this:
insert into foodchoices (notunique) values ('test')
BUT, if it is a field that does already exist, I WILL have that unique value. Is there some form of wildcard or something I can use for when I do not have the unique value?
I believe the answer to this is addressed in the MySQL docs:
If a table contains an AUTO_INCREMENT column and INSERT ... UPDATE inserts a row, the LAST_INSERT_ID() function returns the AUTO_INCREMENT value. If the statement updates a row instead, LAST_INSERT_ID() is not meaningful. However, you can work around this by using LAST_INSERT_ID(expr). Suppose that id is the AUTO_INCREMENT column. To make LAST_INSERT_ID() meaningful for updates, insert rows as follows:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), c=3;
I think what you just might try to do is select the row with the value you have (if exists then update) otherwise insert. It's just one more sentence.
I just don't see how can you compare an existing value that you just don't have (the generated ID). Plus, if the ID is DB seeded how it'll be duplicated?
May be you need to alter your table structure for adding any constraint to "notunique" column. So you can:
insert into foodchoices (notunique) values ('test') on duplicate key update columntostoreyouruniqueid = unique;
if notunique has no constaint then it mean that you will have uniqueid as set. So it has to double query.

SQL Upon finding duplicate key, replace entire entry

I have an insert query for MySQL that looks like this:
INSERT INTO table (foo, bar, fooo, baar, etc) VALUES (?,?,?,?,?)
It is used in a script to migrate some columns and keeps encountering duplicate primary keys. (Old database was awful and poorly maintained).
Is there a way I can just tell it to replace the whole offending row with the current values tossing out the old stuff entirely? I know there is an ON DUPLICATE KEY UPDATE command, but I don't know if it would help me as all I've seen it used for is incrementing.
ANSWER: INSERT INTO table (foo, bar, fooo, baar, etc) VALUES (?,?,?,?,?) ON DUPLICATE KEY UPDATE foo=?, bar=?, fooo=?, baar=?, etc=?
Keep in mind that you have to add the values in the referenced array again to account for the extra question marks.
on duplicate key update should work, as should a replace statement.
From MySQL manual:
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.
What you said:
Is there a way I can just tell it to
replace the whole offending row with
the current values tossing out the old
stuff entirely?
Conclusion: why don't you just try it? It seems it does exactly what you want.
Edit: Since you haven't provided any examples of what you were trying to do, I'll use some from MySQL's website.
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
Or if you want something that relates more to real world:
INSERT INTO table(int_field, str_field, float_field) VALUES (15, 'some string', '1.22')
ON DUPLICATE KEY UPDATE int_field = 15, str_field = 'some_string', float_field = '1.22';

Is there "UPDATE value IF NO SUCH ROW INSERT yyy" in MySQL?

I want to update a table value on Mysql 5 but if the key does not exist create it.
The way I found to do it is by:
INSERT yyy ON DUPLICATE KEY UPDATE field;
The question is : is the format above less efficient than other ways to do it (As the insert will happen only once and update will happen very often)?
for example:
$result = UPDATE field;
if (num_rows_effected($result)==0) INSERT yyy
Furthermore: Is there a better way to do this in Mysql: for example a kind of:
UPDATE value IF NO SUCH ROW INSERT yyy;
Update: For those who suggested REPLACE, here is an extension to my question:
"Thanks! I need to increase a counter that is already in the table (if it exists). If not create a table row with value 1 for this column. How can I do update with this format (REPLACE)? "
There is a REPLACE also.
INSERT ON DUPLICATE KEY UPDATE will fire UPDATE triggers when it will stumble upon a duplicate key and won't violate FK's in case on UPDATE.
REPLACE will fire DELETE and INSERT triggers, and will violate FK's referencing the row being REPLACE'd.
If you don't have any triggers or FK's, then use INSERT ON DUPLICATE KEY UPDATE, it's most efficient.
You seem to be looking for this query:
INSERT
INTO table (key, counter)
VALUES (#key, 1)
ON DUPLICATE KEY UPDATE
counter = counter + 1
You cannot do this with REPLACE unless you have selected previous value of the counter before running the query.
P. S. REPLACE appeared in MySQL before ON DUPLICATE KEY UPDATE and is being kept only for compatibility. There is no performance increase from using it.
Yes, you can use the 'replace' syntax:
REPLACE INTO table1 (key, col1, col2) values (1, 'val1','val2');
This is a feature specific to MySQL and is not necessarily implemented in other databases.
As for efficiency, my guess is that a straight update will be faster, since MySQL essentially catches the duplicate key error and handles it accordingly. However, unless you are doing large amounts of insert/updates, the performance impact will be fairly small.
Look at the REPLACE command, it meets your requirements.