I am using PreparedStatement to prepare sql queries. I want to insert a row in table if and only if it doesn't exist.
I tried this -
INSERT INTO users (userId) VALUES (?) ON DUPLICATE KEY UPDATE userId = ?
But this will unnecessarily update the userId.
How can i insert the userId here ?
INSERT INTO users
(userId)
SELECT ?
WHERE NOT EXISTS
(
SELECT *
FROM users
where userId = ?
)
You may use
INSERT IGNORE INTO users (userId) VALUES (?)
But you should understand why do you want ignore errors.
on duplicate key does not work correctly when the table is an innodb. It creates exactly the problem you are describing. If you need the functionality of an innodb, then should you first check the existence of the row, otherwise can you convert the table to a myisam table.
edit: if you need to check the existence of the row before the decision to insert or update, then would I advice you to use a stored procedure.
DELIMITER //
CREATE PROCEDURE adjustusers(IN pId int)
BEGIN
DECLARE userid int;
select count(id) into userid from users where id = pId;
if userid = 1 then
update users set id = pId where id = pId;
else
insert into users(id) values(pId);
end if;
END //
DELIMITER ;
A stored procedure is precompiled, just as a prepared statement. Hence no SQL injection problems and some more functionality and only one call to the database.
Related
I have a table accounts in Postgres which had id and name as fields. id is the primary key.
I want to fetch the last primary key inserted into the table using this query :-
select id from accounts order by id desc limit 1 ;
Using a preparedStatement I run this query and get the value for my next primary key by incrementing it by 1.
String query="SELECT "+columnName+" FROM "+TableName+" ORDER BY "+columnName+" DESC limit 1";
PreparedStatement stmt=conn.prepareStatement(query);
ResultSet rs= stmt.executeQuery();
int counter= rs.getInt(1);
My question is if there are 0 rows, what will be the counter value?
If the value is null which i don't think can be stored in int, how do I assign it a starting primary int key value say 10 ?
You shouldn't be doing that, so here's what I believe is the best answer.
Instead, define your id as auto-incrementing which postgres manages:
create table account (
id serial not null primary key,
...
)
Then execute an insert:
insert into account (col1, col2, ...) values (..., ...) -- omit id
And the new account will get the next number, which you can get from the result returned from the insert, or in postgres you can use a regular query to get it
insert into account (col1, col2, ...) values (..., ...) -- omit id
returning id
Note the change in name from accounts to account - naming tables are a singular noun is best practice and makes sense: accounts.surname is nonsense, but account.surname is how we speak and think.
I'm trying to write a java sql query, the simplified table would be table(name,version) with a unique constraint on (name, version).
I'm trying to insert a row into my database with a conditional statement. Meaning that when a entry with the same name exists, it should insert the row with same name and its version increased by 1.
I have tried with the following:
INSERT INTO table(name,version)
VALUES(?, CASE WHEN EXISTS(SELECT name from table where name=?)
THEN (SELECT MAX(version) FROM table WHERE name = ?) +1
ELSE 1 END)
values are sent by user.
My question is, how can I access the 'name' inside the values so I could compare them?
If you want to write this as a single query:
INSERT INTO table (name, version)
SELECT ?, COLAESCE(MAX(t2.version) + 1, 1)
FROM table t2
WHERE t2.name = ?;
That said, this is dangerous. Two threads could execute this query "at the same time" and possibly create the same version number. You can prevent this from happening by adding a unique index/constraint on (name, version).
With the unique index/constraint, one of the updates will fail if there is a conflict.
I see at least two approaches:
1. For each pair of name and version you first query the max version:
SELECT MAX(VERSION) as MAX FROM <table> WHERE NAME = <name>
And then you insert the result + 1 with a corresponding insert query:
INSERT INTO <table>(NAME,VERSION) VALUES (<name>,result+1)
This approach is very straight-forward, easy-to-read and implement, however, not really performant because of so many queries necessary.
You can achieve that with sql alone with sql analytics and window functions, e.g.:
SELECT NAME, ROW_NUMBER() over (partition BY NAME ORDER BY NAME) as VERSION FROM<table>
You can then save the result of this query as a table using CREATE TABLE as SELECT...
(The assumption here is that the first version is 1, if it is not the case, then one could slightly rework the query). This solution would be very performant even for large datasets.
You should get the name before insertion. In your case, if something went wrong then how would you know about it so you get the name before insert query.
Not sure but you try this:
declare int version;
if exists(SELECT name from table where name=?)
then
version = SELECT MAX(version) FROM table WHERE name = ?
version += 1
else
version = 1
end
Regards.
This is actually a bad plan, you might be changing what the user's specified data. That is likely to not be what is desired, maybe they're not trying to create a new version but just unaware that the one wanted already exists. But, you can create a function, which your java calls, not only inserts the requested version or max+1 if the requested version already exists. Moreover it returns the actual values inserted.
-- create table
create table nv( name text
, version integer
, constraint nv_uk unique (name, version)
);
-- function to create version or 1+max if requested exists
create or replace function new_version
( name_in text
, version_in integer
)
returns record
language plpgsql strict
as $$
declare
violated_constraint text;
return_name_version record;
begin
insert into nv(name,version)
values (name_in,version_in)
returning (name, version) into return_name_version;
return return_name_version;
exception
when unique_violation
then
GET STACKED DIAGNOSTICS violated_constraint = CONSTRAINT_NAME;
if violated_constraint like '%nv\_uk%'
then
insert into nv(name,version)
select name_in, 1+max(version)
from nv
where name = name_in
group by name_in
returning (name, version) into return_name_version;
return return_name_version;
end if;
end;
$$;
-- create some data
insert into nv(name,version)
select 'n1', gn
from generate_series( 1,3) gn ;
-- test insert existing
select new_version('n2',1);
select new_version('n1',1);
select *
from nv
order by name, version;
I am new to MySQL and I wrote a simple query bellow:
CREATE Table tblFeedBack
(
`FeedBackID` INT AUTO_IncremeNT,
`UserID` INT,
`Inserted_TS` TIMESTAMP ,
`FeedBackValue` VARCHAR(100),
PRIMARY KEY (FeedBackID)
);
CREATE PROCEDURE tblFeedBack_InsertUpdate
(
IN U_ID INT,
IN FB_Value VARCHAR(50)
)
BEGIN
IF ((Select COUNT(*) From 'tblFeedback') < 3)
BEGIN
INSERT INTO 'tblFeedBack' (`UserID`,`FeedBackValue`)
VALUES (U_ID,FB_Value);
END
ELSE
BEGIN
DECLARE #MostRecentFID INT;
SELECT TOP 1 `FeedBackID` FROM tblFeedback
WHERE UID = U_ID
ORDER BY `Inserted_TS` DESC
INTO #MostRecentFID;
UPDATE tblfeedback
SET `FeedBackValue` = #FeedBackValue
WHERE `FeedBackID` = #MostRecentFID
END
END
I am getting this error:
Schema Creation Failed: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''tblFeedBack' (`UserID`,`FeedBackValue`) VALUES (1,'12')' at line 9
Can anyone please help me solve this one?
Thanks in advance.
MySQL does not support TOP you want to use LIMIT 1 instead as they are ordered.
Select `FeedBackID` FROM tblFeedback
WHERE UID = U_ID
ORDER BY `Inserted_TS` DESC
LIMIT 1
INTO #MostRecentFID;
Also, when you query a table using quotes it becomes case sensitive.
IF ((Select COUNT(*) From 'tblFeedback') < 3)
Should be
IF ((Select COUNT(*) From 'tblFeedBack') < 3)
Fix these 2 errors and it should work.
The table names are different in the insert query. One contains 'tblFeedback' and other contains 'tblFeedBack'
Also, please try to remove single quotes near table names in the query.
With jooq 3.4 I can't figure out how to do this (with Postgresql):
Query query = dsl.insertInto(TABLE)
.set(TABLE.ID, Sequences.TABLE_ID_SEQ.nextval());
but in a case when I don't know which is the exact table, something like this:
TableImpl<?> tableImpl;
Query query = dsl.insertInto(tableImpl)
.set(tableImpl.getIdentity(), tableImpl.getIdentity().getSequence().nextval());
Is it somehow possible?
I tried this:
dsl.insertInto(tableImpl)
.set(DSL.field("id"),
tableImpl.getSchema().getSequence("table_id_seq").nextval())
This works but I still don't know how to get the sequence name from the TableImpl object.
Is there a solution for this? Or is there a problem with my approach?
In plain SQL I would do this:
insert into table_A (id) VALUES nextval('table_A_id_seq');
insert into table_B (table_A_id, some_val) VALUES (currval('table_A_id_seq'), some_val);
So I need the value or a reference to that id for later use of the id that was generated for the inserted record as default, but I don't want to set any other values.
jOOQ currently doesn't have any means of associating a table with its implicitly used sequence for the identity column. The reason for this is that the sequence is generated when the table is created, but it isn't formally connected to that table.
Usually, you don't have to explicitly set the serial value of a column in a PostgreSQL database. It is generated automatically on insert. In terms of DDL, this means:
CREATE TABLE tablename (
colname SERIAL
);
is equivalent to specifying:
CREATE SEQUENCE tablename_colname_seq;
CREATE TABLE tablename (
colname integer NOT NULL DEFAULT nextval('tablename_colname_seq')
);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;
The above is taken from:
http://www.postgresql.org/docs/9.3/static/datatype-numeric.html#DATATYPE-SERIAL
In other words, just leave out the ID values from the INSERT statements.
"Empty" INSERT statements
Note that if you want to create an "empty" INSERT statement, i.e. a statement where you pass no values at all, generating a new column with a generated ID, you can use the DEFAULT VALUES clause.
With SQL
INSERT INTO tablename DEFAULT VALUES
With jOOQ
DSL.using(configuration)
.insertInto(TABLENAME)
.defaultValues()
.execute();
Returning IDs
Note that PostgreSQL has native support for an INSERT .. RETURNING clause, which is also supported by jOOQ:
With SQL
INSERT INTO tablename (...) VALUES (...) RETURNING ID
With jOOQ
DSL.using(configuration)
.insertInto(TABLENAME, ...)
.values(...)
.returning(TABLENAME.ID)
.fetchOne();
I'm pretty new to MySQL. I have two related tables, quite common case: Klients(KID, name, surname) and Visits(VID, VKID, dateOfVisit) - VKID is the Klient ID. I have a problem with suitable INSERT query, this is what I want to do:
1.Check if Klient with specific name and surname exists (let's assume that there are no people with the same surnames)
2.If yes, get the ID and do the INSERT to Visits table
3.If no, INSERT new Klient, get the ID and INSERT to Visits.
Is it possible to do in one query?
You would need to use the IF EXIST / NOT EXISTS and use a subquery to check the table. See the reference bwlo
http://dev.mysql.com/doc/refman/5.0/en/exists-and-not-exists-subqueries.html
HTH
The INSERT statement allows only one single target table.
So the query you're looking for is just impossible unless you use triggers or stored procedures.
But such problem is commonly solved using the fallowing small algorithm:
1) insert a record in table [Visits] assuming the parent record does exist in table [Klients]
INSERT INTO Visits (VKID, dateOfVisit)
SELECT KID, NOW()
FROM Klients
WHERE (name=#name) AND (surname=#surname)
2) check the number of inserted records after query (1)
3) if no record has been inserted, then add a new record table [Klients], and then run (1) again.
try something like this
IF (SELECT * FROM `sometable` WHERE name = 'somename' AND surname = 'somesurname') IS NULL THEN
INSERT INTO Table1(name,surname) VALUES ('somename', 'somesurname');
ELSE INSERT INTO visits(kid,name,surname)
SELECT kid, name, surname FROM Table1 WHERE name = 'somename' AND surname = 'somesurname';
END IF;
there is no need to specify 'VALUES' on the second insert
i have not tested it, but this is the general idea of what you are trying to accomplish.
These should be two queries in a transaction:
INSERT INTO Klients (name, surname)
VALUES ('John', 'Doe')
ON DUPLICATE KEY UPDATE
KID = LAST_INSERT_ID(KID);
INSERT INTO Visits (VKID, dateOfVisits)
VALUES (LAST_INSERT_ID(), NOW());
The first statement is an upsert statement where the update part uses not widely known, but intented exactly for the purpose functionality of LAST_INSERT_ID(), where explicitly passed value is stored for getting the value afterwards.
UPD: I forgot to mention that you would need to add a unique constraint on (surname, name).