I've tried multiple variations of this code and it keeps giving me the SQL state: 42601 error. I've looked at the docs and tried using their examples which sometimes work, but do not do what I want.
IF (SELECT guildid FROM Servers <> 1) THEN
INSERT INTO Servers (guildid) VALUES (1)
END IF;
My Servers table is simple. I just have a single row called guildid. I do not want a CASE statement because that only outputs messages.
If you don't have to worry about race conditions (which the if approach suggests), then:
INSERT INTO Servers (guildid)
SELECT guildid
FROM (VALUES (1)) v(guildid)
WHERE NOT EXISTS (SELECT 1 FROM Servers s WHERE s.guildid = v.guildid);
To protect the table, I would suggest adding a unique index on it. In fact, just declare guildid to be the primary key. In that case, your original insert will simply fail, if you attempt to insert a duplicate value.
If you have a unique constraint on that column, you can use on conflict do nothing:
INSERT INTO Servers (guildid) VALUES (1)
ON CONFLICT DO NOTHING;
Related
I have a table with ID primary key (autoincrement) and a unique column Name. Is there an efficient way in MariaDB to insert a row into this table if the same Name doesn't exist, otherwise select the existing row and, in both cases, return the ID of the row with this Name?
Here's a solution for Postgres. However, it seems MariaDB doesn't have the RETURNING id clause.
What I have tried so far is brute-force:
INSERT IGNORE INTO services (Name) VALUES ('JohnDoe');
SELECT ID FROM services WHERE Name='JohnDoe';
UPDATE: MariaDB 10.5 has RETURNING clause, however, the queries I have tried so far throw a syntax error:
WITH i AS (INSERT IGNORE INTO services (`Name`) VALUES ('John') RETURNING ID)
SELECT ID FROM i
UNION
SELECT ID FROM services WHERE `Name`='John'
For a single row, assuming id is AUTO_INCREMENT.
INSERT INTO t (name)
VALUES ('JohnDoe')
ON DUPLICATE KEY id = LAST_INSERT_ID(id);
SELECT LAST_INSERT_ID();
That looks kludgy, but it is an example in the documentation.
Caution: Most forms of INSERT will "burn" auto_inc ids. That is, they grab the next id(s) before realizing that the id won't be used. This could lead to overflowing the max auto_inc size.
It is also wise not to put the normalization inside the transaction that does the "meat" of the code. It ties up the table unnecessarily long and runs extra risk of burning ids in the case of rollback.
For batch updating of a 'normalization' table like that, see my notes here: http://mysql.rjweb.org/doc.php/staging_table#normalization (It avoids burning ids.)
I am running a python script that inserts a large amount of data into a Postgres database, I use a single query to perform multiple row inserts:
INSERT INTO table (col1,col2) VALUES ('v1','v2'),('v3','v4') ... etc
I was wondering what would happen if it hits a duplicate key for the insert. Will it stop the entire query and throw an exception? Or will it merely ignore the insert of that specific row and move on?
The INSERT will just insert all rows and nothing special will happen, unless you have some kind of constraint disallowing duplicate / overlapping values (PRIMARY KEY, UNIQUE, CHECK or EXCLUDE constraint) - which you did not mention in your question. But that's what you are probably worried about.
Assuming a UNIQUE or PK constraint on (col1,col2), you are dealing with a textbook UPSERT situation. Many related questions and answers to find here.
Generally, if any constraint is violated, an exception is raised which (unless trapped in subtransaction like it's possible in a procedural server-side language like plpgsql) will roll back not only the statement, but the whole transaction.
Without concurrent writes
I.e.: No other transactions will try to write to the same table at the same time.
Exclude rows that are already in the table with WHERE NOT EXISTS ... or any other applicable technique:
Select rows which are not present in other table
And don't forget to remove duplicates within the inserted set as well, which would not be excluded by the semi-anti-join WHERE NOT EXISTS ...
One technique to deal with both at once would be EXCEPT:
INSERT INTO tbl (col1, col2)
VALUES
(text 'v1', text 'v2') -- explicit type cast may be needed in 1st row
, ('v3', 'v4')
, ('v3', 'v4') -- beware of dupes in source
EXCEPT SELECT col1, col2 FROM tbl;
EXCEPT without the key word ALL folds duplicate rows in the source. If you know there are no dupes, or you don't want to fold duplicates silently, use EXCEPT ALL (or one of the other techniques). See:
Using EXCEPT clause in PostgreSQL
Generally, if the target table is big, WHERE NOT EXISTS in combination with DISTINCT on the source will probably be faster:
INSERT INTO tbl (col1, col2)
SELECT *
FROM (
SELECT DISTINCT *
FROM (
VALUES
(text 'v1', text'v2')
, ('v3', 'v4')
, ('v3', 'v4') -- dupes in source
) t(c1, c2)
) t
WHERE NOT EXISTS (
SELECT FROM tbl
WHERE col1 = t.c1 AND col2 = t.c2
);
If there can be many dupes, it pays to fold them in the source first. Else use one subquery less.
Related:
Select rows which are not present in other table
With concurrent writes
Use the Postgres UPSERT implementation INSERT ... ON CONFLICT ... in Postgres 9.5 or later:
INSERT INTO tbl (col1,col2)
SELECT DISTINCT * -- still can't insert the same row more than once
FROM (
VALUES
(text 'v1', text 'v2')
, ('v3','v4')
, ('v3','v4') -- you still need to fold dupes in source!
) t(c1, c2)
ON CONFLICT DO NOTHING; -- ignores rows with *any* conflict!
Further reading:
How to use RETURNING with ON CONFLICT in PostgreSQL?
How do I insert a row which contains a foreign key?
Documentation:
The manual
The commit page
The Postgres Wiki page
Craig's reference answer for UPSERT problems:
How to UPSERT (MERGE, INSERT ... ON DUPLICATE UPDATE) in PostgreSQL?
Will it stop the entire query and throw an exception? Yes.
To avoid that, you can look on the following SO question here, which describes how to avoid Postgres from throwing an error for multiple inserts when some of the inserted keys already exist on the DB.
You should basically do this:
INSERT INTO DBtable
(id, field1)
SELECT 1, 'value'
WHERE
NOT EXISTS (
SELECT id FROM DBtable WHERE id = 1
);
In a database application, I want to insert, update and delete records in a table of database.
Table is as below:
In this table, Ga1_ID is Primary Key.
Suppose, I insert 5 records as show currently.
In second attempt, if I want to insert 5 other records and if any of these new records contains a primary key attribute which is already present in table it show error. Its fine.
But, when I insert new 5 records... how I can verify these new records's primary key value is not present. I mean, how to match or calculate the already present primary key attributes and then insert new records.
What is the best approach to manage this sort of situation ?
use following query in dataadapter:
da=new SqlDataAdapter("select Ga1_ID from table where Ga1_ID=#pkVal",conn);
DataSet=new DataSet();
da.fill(ds);
//pass parameter for #pkVal
da.SelectCommand.Parameters(1).Value = pkValue;
if(ds.Tables[0].Rows.Count>0) //If number of rows >0 then record exists
BEGIN
messagebox.show("Primary key present");
END
Hope its helpful.
Do not check existing records in advance, i.e. do not SELECT and then INSERT. A better (and pretty common) approach is to try to INSERT and handle exceptions, in particular, catch a primary key violation if any and handle it.
Do the insert in a try/catch block, with different handling in case of a primary key violation exception and other sql exception types.
If there was no exception, then job's done, record was inserted.
If you caught a primary key violation exception, then handle it appropriately (your post does not specify what you want to do in this case, and it's completely up to you)
If you want to perform 5 inserts at once and want to make sure they all succeed or else roll back if any of them failed, then do the inserts within a transaction.
you can do a lookup first before inserting.
IF EXISTS (SELECT * FROM tableName WHERE GA1_id=#newId)
BEGIN
UPDATE tableName SET Ga1_docid = #newdocID, GA1_fieldNAme = #newName, Ga1_fieldValue = #newVal where GA1_id=#newId
END
ELSE
BEGIN
INSERT INTO tableName(GA1_ID, Ga1_docid, GA1_fieldNAme Ga1_fieldValue) VALUES (value1,val2,value3,value4)
END
If you're using SQL Server 2012, use a sequence object - CREATE SEQUENCE.
This way you can get the next value using NEXT VALUE FOR.
With an older SQL Server version, you need to create the primary key field as an IDENTITY field and use the SCOPE_IDENTITY function to get the last identity value and then increment it manually.
Normally, you would like to have a surrogate key wich is generally an identity column that will automatically increment when you are inserting rows so that you don't have to care about knowing which id already exists.
However, if you have to manually insert the id there's a few alternatives for that and knowing wich SQL database you are using would help, but in most SQL implementations, you should be able to do something like:
IF NOT EXISTS
IF NOT EXISTS(
SELECT 1
FROM your_table
WHERE Ga1_ID = 1
)
INSERT INTO ...
SELECT WHERE NOT EXISTS
INSERT INTO your_table (col_1, col_2)
SELECT col_1, col_2
FROM (
SELECT 1 AS col_1, 2 AS col_2
UNION ALL
SELECT 3, 4
) q
WHERE NOT EXISTS (
SELECT 1
FROM your_table
WHERE col_1 = q.col_1
)
For MS SQL Server, you can also look at the MERGE statement and for MySQL, you can use the INSERT IGNORE statement.
I want to insert a row if it doesn't already exist. If it does already exist, I want to get it's primary key.
Can this be done without using two queries, for instance using a UNIQUE constraint on the columns and ON CONFLICT ... TELL ME THE CONFLICTING ROWID?
Please note that I don't have experience with SQLite. However, after perusing the online documentation, I don't believe that it supports data-change table references, so no, this isn't possible.
My reccommendation is to write your INSERT in such a way that it won't fail if the row exists - it just won't insert a row. Something like this:
INSERT INTO destinationTable (colA, colB)
(SELECT :colAValue, :colBValue
WHERE NOT EXISTS (SELECT '1'
FROM destinationTable
WHERE uniqueColumn = :uniqueColumn))
This works because the selection won't return a row if it already exists. You can then either look at the return code/state to see if it INSERTed a row, or just SELECT with the unique column, to get the identity column.
DON'T rely on your constraint to catch this. Constraints are to catch application errors, and this is solely a business/implementation detail.
In a word, no. You can't, with SQLite, either INSERT data or, on some condition, SELECT it.
Other SQL engines might allow it, but SQLite can't.
What you can do is INSERT OR IGNORE, which will just not bring up an error. See http://sqlite.org/lang_conflict.html
We have a status table. When the status changes we currently delete the old record and insert a new.
We are wondering if it would be faster to do a select to check if it exists followed by an insert or update.
Although similar to the following question, it is not the same, since we are changing individual records and the other question was doing a total table refresh.
DELETE, INSERT vs UPDATE || INSERT
Since you're talking SQL Server 2008, have you considered MERGE? It's a single statement that allows you to do an update or insert:
create table T1 (
ID int not null,
Val1 varchar(10) not null
)
go
insert into T1 (ID,Val1)
select 1,'abc'
go
merge into T1
using (select 1 as ID,'def' as Val1) upd on T1.ID = upd.ID --<-- These identify the row you want to update/insert and the new value you want to set. They could be #parameters
when matched then update set Val1 = upd.Val1
when not matched then insert (ID,Val1) values (upd.ID,upd.Val1);
What about INSERT ... ON DUPLICATE KEY? First doing a select to check if a record exists and checking in your program the result of that creates a race condition. That might not be important in your case if there is only a single instance of the program however.
INSERT INTO users (username, email) VALUES ('Jo', 'jo#email.com')
ON DUPLICATE KEY UPDATE email = 'jo#email.com'
You can use ##ROWCOUNT and perform UPDATE. If it was 0 rows affected - then perform INSERT after, nothing otherwise.
Your suggestion would mean always two instructions for each status change. The usual way is to do an UPDATE and then check if the operation changed any rows (Most databases have a variable like ROWCOUNT which should be greater than 0 if something changed). If it didn't, do an INSERT.
Search for UPSERT for find patterns for your specific DBMS
Personally, I think the UPDATE method is the best. Instead of doing a SELECT first to check if a record already exists, you can first attempt an UPDATE but if no rows are affected (using ##ROWCOUNT) you can do an INSERT.
The reason for this is that sooner or later you might want to track status changes, and the best way to do this would be to keep an audit trail of all changes using a trigger on the status table.