I am trying to write a DB2 query that allows me to either update a record if it already exists but if it does not exist it should be inserted. I wrote the following query that should accomplish this:
MERGE INTO OA1P.TLZ712A1 AS PC
USING (
SELECT * FROM OA1P.TLZ712A1
WHERE CALENDAR_ID=13 AND
"PACKAGE"='M2108'
) PC2
ON (PC.ID_PACKAGE_CALENDAR=PC2.ID_PACKAGE_CALENDAR)
WHEN MATCHED THEN
UPDATE SET ACT_DATE = '31.12.2021'
WHEN NOT MATCHED THEN
INSERT ("PACKAGE", ACT_DATE, CALENDAR_ID, PREPTA, MIXED) VALUES ('M2108', '31.12.2021', 13, 0, 0)
This query should attempt to check if a record already exists for the selection criteria. Updating a record seems to be working fine but I am not able to get the "WHEN NOT MATCHED" part to work and inserting a new record. Anyone able to provide some assistance?
The table is used to save the activation date of a certain software package. PACKAGE is the reference to the package table containing the name of the package (eg. "M2108"). CALENDAR_ID refers to a system where the software package will be activated. The actual date is stored in ACT_DATE.
Did not manage to get the DDL into SQLFiddle so I have to provide it here:
CREATE TABLE OA1P.TLZ712A1 (
ID_PACKAGE_CALENDAR INTEGER DEFAULT IDENTITY GENERATED BY DEFAULT NOT NULL,
CALENDAR_ID INTEGER,
"PACKAGE" VARCHAR(10) NOT NULL,
ACT_DATE DATE NOT NULL,
PREPTA SMALLINT DEFAULT 0 NOT NULL,
MIXED SMALLINT DEFAULT 0 NOT NULL,
"COMMENT" VARCHAR(60) NOT NULL,
LAST_MODIFIED_PID CHAR(7) NOT NULL,
ST_STARTID TIMESTAMP NOT NULL,
ST_FROM TIMESTAMP NOT NULL,
ST_TO TIMESTAMP NOT NULL,
CONSTRAINT TLZ712A1_PK PRIMARY KEY (ID_PACKAGE_CALENDAR),
CONSTRAINT CALENDAR FOREIGN KEY (CALENDAR_ID) REFERENCES OA1P.TLZ711A1(ID_CALENDAR) ON DELETE RESTRICT,
CONSTRAINT "PACKAGE" FOREIGN KEY ("PACKAGE") REFERENCES OA1P.TLZ716A1(NAME) ON DELETE RESTRICT
);
CREATE UNIQUE INDEX ILZ712A0 ON OA1P.TLZ712A1 (ID_PACKAGE_CALENDAR);
If your goal is to set ACT_DATE to 31.12.2021 if a row is found with PACKAGE = M2108 and CALENDAR_ID = 13 and if no row is found with these values then insert it, then this could be the answer
MERGE INTO OA1P.TLZ712A1 AS PC
USING (
VALUES ('M2108', 13, date '31.12.2021')
) PC2 ("PACKAGE", CALENDAR_ID, ACT_DATE)
ON (PC."PACKAGE", PC.CALENDAR_ID) = (PC2."PACKAGE", PC2.CALENDAR_ID)
WHEN MATCHED THEN
UPDATE SET ACT_DATE = PC2.ACT_DATE
WHEN NOT MATCHED THEN
INSERT ("PACKAGE", ACT_DATE, CALENDAR_ID, PREPTA, MIXED) VALUES (PC2."PACKAGE", PC2.ACT_DATE, PC2.CALENDAR_ID, 0, 0)
Related
I'm working on a database for my school project in which I have to produce a functional database by normalizing sample tables given to us.
One table I'm having trouble with is itineraries. I produce 3 tables from the normalization which are "Destinations", "Itineraries" and "Itinerary_Destinations".
The code for Destinations is:
create table Destinations
(
DestinationID varchar(5) primary key,
Name varchar(45)
);
The code for Itineraries is:
create table Itineraries
(
ItineraryID varchar(5),
Name varchar(45)
);
The code for the last table is:
create table Itinerary_Destinations
(
DI varchar(5) primary key,
ItineraryID varchar(5) foreign key references Itineraries(ItineraryID),
Itinerary_Name varchar(45),
DestinationID varchar(5) foreign key references Destinations(DestinationID),
Destination_Name varchar(45)
);
Data has already been inserted into all 3 tables with the exception of 'Destination_Name' and 'Itinerary_Name' columns. The code I'm attempting to use is returning as error. The code is shown below.
insert into Itinerary_Destinations (Itinerary_name)
select Name from Itineraries where
Itineraries.ItineraryID = ItineraryID;
The error it returns is
Msg 515, Level 16, State 2, Line 1 Cannot insert the value NULL into
column 'DI', table 'DDDAssignment.dbo.Itinerary_Destinations'; column
does not allow nulls. INSERT fails. The statement has been terminated.
Is there a method to accomplish the task of inserting the Destination_Name and Itinerary_Name without creating new records that require primary keys?
Or should I do it manually?
If you want to modify records which already exist, then you should be using an UPDATE rather than an INSERT:
UPDATE a
SET Itinerary_name = b.Name
FROM Itinerary_Destinations a
INNER JOIN Itinerary_name b
ON a.ItineraryID = b.ItineraryID;
But, if you do have some data which is not already logically associated with the Itinerary_Destinations table, then using an insert is appropriate.
use coalesce funtion in case null it will insert blank string, as your column does not allow null value thats why you got that error in your query
insert into Itinerary_Destinations (Itinerary_name)
select coalesce(Name,' ') from Itineraries where
Itineraries.ItineraryID = ItineraryID;
I have created a table and I'm asked to add a constraint to a column called no_semesters. the condition is that the no has to be >= 0 and it should be not null with default, and the default value is 6. When I run this statement:
INSERT INTO PREMIERD08/PGM (PGM_ID, PGM_NAME)
VALUES('CPD', 'COMPUTER PROGRAMMING')
I get an error message saying column - no_semesters cant be null. why wont it set to the default value which is 6?
this was the statement -
CREATE TABLE PREMIERD08/PGM (
PGM_ID CHAR(3) NOT NULL,
PGM_NAME CHAR(40) NOT NULL,
NO_SEMESTERS NUMERIC ( 1) NOT NULL WITH DEFAULT 6,
CONSTRAINT PGM_PGM_NAME_UK UNIQUE (PGM_NAME),
CONSTRAINT PGM_PGM_ID_CK CHECK (PGM_ID IN ('CPA', 'CPD') ),
CONSTRAINT PGM_PGM_ID_PK PRIMARY KEY (PGM_ID), CONSTRAINT PGM_NO_SEMESTERS_CK CHECK (NO_SEMESTERS >= 0)
)
Your code works in Db2 (for LUW) - the only thing to change is the table name needs to be in "" because of the /
CREATE TABLE "PREMIERD08/PGM" .....
INSERT INTO "PREMIERD08/PGM" (PGM_ID, PGM_NAME)
VALUES('CPD', 'COMPUTER PROGRAMMING')
How can I enforce a table to have only one row? Below is what I tried. The UPDATE trigger might work, however, the CREATE trigger definitely will not. For the CREATE, I would like to use SET, however, SET is not supported by SQLite.
CREATE TABLE IF NOT EXISTS `config` (
`id` TINYINT NOT NULL DEFAULT 0,
`subdomain` VARCHAR(45) NOT NULL,
`timezone` CHAR(3) NOT NULL,
`timeout` TINYINT NOT NULL,
`offline` TINYINT NOT NULL,
`hash_config` CHAR(32) NOT NULL,
`hash_points` CHAR(32) NOT NULL,
PRIMARY KEY (`id`));
INSERT INTO config(id,subdomain,timezone,timeout,offline,hash_config,hash_points) VALUES(0,'subdomain','UTC',5,0,'hash_config','hash_points');
CREATE TRIGGER `config_insert_zero`
BEFORE INSERT ON `config`
FOR EACH ROW
BEGIN
-- SET NEW.id=0;
NEW.id=OLD.id;
END;
CREATE TRIGGER `config_update_zero`
BEFORE UPDATE ON `config`
FOR EACH ROW
BEGIN
-- SET NEW.id=0;
NEW.id=OLD.id;
END;
In the general case, to limit the number of rows in a table, you have to prevent any further insert.
In SQLite, this is done with RAISE():
CREATE TRIGGER config_no_insert
BEFORE INSERT ON config
WHEN (SELECT COUNT(*) FROM config) >= 1 -- limit here
BEGIN
SELECT RAISE(FAIL, 'only one row!');
END;
However, if the limit is one, you could instead simply constrain the primary key to a fixed value:
CREATE TABLE config (
id INTEGER PRIMARY KEY CHECK (id = 0),
[...]
);
One idea you may want to consider is to make it appear like the table has only one row. In reality, you keep all previous rows because it's quite possible you will one day want to maintain a history of all past values.
Since there is only one row, there really is no need for an ID column, the purpose of which is to uniquely differentiate each row from all the others. You do need, however, a timestamp which will be used to identify the "one row" which will be the latest row written to the table.
CREATE TABLE `config_history` (
`created` timestamp default current_timestamp,
`subdomain` VARCHAR(45) NOT NULL,
`timezone` CHAR(3) NOT NULL,
`timeout` TINYINT NOT NULL,
`offline` TINYINT NOT NULL,
`hash_config` CHAR(32) NOT NULL,
`hash_points` CHAR(32) NOT NULL,
PRIMARY KEY (`created`)
);
Since you are normally interested in only the last row written (the latest version), the query selects the row with the latest creation date:
select ch.created effective_date, ch.subdomain, ch.timezone, ch.timeout,
ch.offline, ch.hash_config, ch.hash_points
from config_history ch
where ch.created =(
select max( created )
from config_history );
Put a create view config as in front of this query and you have a view that selects only one row, the latest, from the table. Any query against the view returns the one row:
select *
from config;
An instead of trigger on the view can convert Updates to Inserts -- you don't actually want to change a value, just write a new row with the new values. This then becomes the new "current" row.
Now you have what appears to be a table with only one row but you also maintain a complete history of all the past changes ever made to that row.
I have a table with the following definition:
CREATE TABLE url_tracker (
id int not null identity(1, 1),
active bit not null,
install_date int not null,
partner_url nvarchar(512) not null,
local_url nvarchar(512) not null,
public_url nvarchar(512) not null,
primary key(id)
);
And I have a requirement that these three URLs always be unique - any individual URL can appear many times, but the combination of the three must be unique (for a given day).
Initially I thought I could do this:
CREATE UNIQUE INDEX uniques ON url_tracker
(install_date, partner_url, local_url, public_url);
However this gives me back the warning:
Warning! The maximum key length is 900 bytes. The index 'uniques' has maximum
length of 3076 bytes. For some combination of large values, the insert/update
operation will fail.
Digging around I learned about the INCLUDE argument to CREATE INDEX, but according to this question converting the command to use INCLUDE will not enforce uniqueness on the URLs.
CREATE UNIQUE INDEX uniques ON url_tracker (install_date)
INCLUDE (partner_url, local_url, public_url);
How can I enforce uniqueness on several relatively large nvarchar fields?
Resolution
So from the comments and answers and more research I'm concluding I can do this:
CREATE TABLE url_tracker (
id int not null identity(1, 1),
active bit not null,
install_date int not null,
partner_url nvarchar(512) not null,
local_url nvarchar(512) not null,
public_url nvarchar(512) not null,
uniquehash AS HashBytes('SHA1',partner_url+local_url+public_url) PERSISTED,
primary key(id)
);
CREATE UNIQUE INDEX uniques ON url_tracker (install_date,uniquehash);
Thoughts?
I would make a computed column with the hash of the URLs, then make a unique index/constraint on that. Consider making the hash a persisted computed column. It shouldn't have to be recalculated after insertion.
Following the ideas from the conversation in the comments. Assuming that you can change the datatype of the URL to be VARCHAR(900) (or NVARCHAR(450) if you really think you need Unicode URLs) and be happy with the limitation on the length of the URL, this solution could work. This also assumes SQL Server 2008 or better. Please, always specify what version you're working with; sql-server is not specific enough, since solutions can vary greatly depending on the version.
Setup:
USE tempdb;
GO
CREATE TABLE dbo.urls
(
id INT IDENTITY(1,1) PRIMARY KEY,
url VARCHAR(900) NOT NULL UNIQUE
);
CREATE TABLE dbo.url_tracker
(
id INT IDENTITY(1,1) PRIMARY KEY,
active BIT NOT NULL DEFAULT 1,
install_date DATE NOT NULL DEFAULT CURRENT_TIMESTAMP,
partner_url_id INT NOT NULL REFERENCES dbo.urls(id),
local_url_id INT NOT NULL REFERENCES dbo.urls(id),
public_url_id INT NOT NULL REFERENCES dbo.urls(id),
CONSTRAINT unique_urls UNIQUE
(
install_date,partner_url_id, local_url_id, public_url_id
)
);
Insert some URLs:
INSERT dbo.urls(url) VALUES
('http://msn.com/'),
('http://aol.com/'),
('http://yahoo.com/'),
('http://google.com/'),
('http://gmail.com/'),
('http://stackoverflow.com/');
Now let's insert some data:
-- succeeds:
INSERT dbo.url_tracker(partner_url_id, local_url_id, public_url_id)
VALUES (1,2,3), (2,3,4), (3,4,5), (4,5,6);
-- fails:
INSERT dbo.url_tracker(partner_url_id, local_url_id, public_url_id)
VALUES(1,2,3);
GO
/*
Msg 2627, Level 14, State 1, Line 3
Violation of UNIQUE KEY constraint 'unique_urls'. Cannot insert duplicate key
in object 'dbo.url_tracker'. The duplicate key value is (2011-09-15, 1, 2, 3).
The statement has been terminated.
*/
-- succeeds, since it's for a different day:
INSERT dbo.url_tracker(install_date, partner_url_id, local_url_id, public_url_id)
VALUES('2011-09-01',1,2,3);
Cleanup:
DROP TABLE dbo.url_tracker, dbo.urls;
Now, if 900 bytes is not enough, you could change the URL table slightly:
CREATE TABLE dbo.urls
(
id INT IDENTITY(1,1) PRIMARY KEY,
url VARCHAR(2048) NOT NULL,
url_hash AS CONVERT(VARBINARY(32), HASHBYTES('SHA1', url)) PERSISTED,
CONSTRAINT unique_url UNIQUE(url_hash)
);
The rest doesn't have to change. And if you try to insert the same URL twice, you get a similar violation, e.g.
INSERT dbo.urls(url) SELECT 'http://www.google.com/';
GO
INSERT dbo.urls(url) SELECT 'http://www.google.com/';
GO
/*
Msg 2627, Level 14, State 1, Line 1
Violation of UNIQUE KEY constraint 'unique_url'. Cannot insert duplicate key
in object 'dbo.urls'. The duplicate key value is
(0xd111175e022c19f447895ad6b72ff259552d1b38).
The statement has been terminated.
*/
In PostgreSql, one can define a sequence and use it as the primary key of a table. In HsqlDB, one can still accomplish creating an auto-increment identity column which doesn't link to any user defined sequence. Is it possible to use a user defined sequence as the generator of an auto-increment identity column in HsqlDB?
Sample sql in PostgreSql:
CREATE SEQUENCE seq_company_id START WITH 1;
CREATE TABLE company (
id bigint PRIMARY KEY DEFAULT nextval('seq_company_id'),
name varchar(128) NOT NULL CHECK (name <> '')
);
What's the equivalent in HsqlDB?
Thanks.
In version 2.0, there is no direct feature for this. You can define a BEFORE INSERT trigger on the table to do this:
CREATE TABLE company ( id bigint PRIMARY KEY, name varchar(128) NOT NULL CHECK (name <> '') );
CREATE TRIGGER trigg BEFORE INSERT
ON company REFERENCING NEW ROW AS newrow
FOR EACH ROW
SET newrow.id = NEXT VALUE FOR seq_company_id;
and insert without using any vlue for id
INSERT INTO company VALUES null, 'test'
Update for HSQLDB 2.1 and later: A feature has been added to support this.
CREATE SEQUENCE SEQU
CREATE TABLE company ( id bigint GENERATED BY DEFAULT AS SEQUENCE SEQU PRIMARY KEY, name varchar(128) NOT NULL CHECK (name <> '') );
See the Guide under CREATE TABLE http://hsqldb.org/doc/2.0/guide/databaseobjects-chapt.html#dbc_table_creation
In addition, 2.1 and later has a PostgreSQL compatibility mode in which it accepts the PostgreSQL CREATE TABLE statement that references the sequence in the DEFAULT clause and translates it to HSQLDB syntax.