I need to set limit to the values of the column. For example, I have a column as TEST_COLUMN with INTEGER data type. I need to set the condition that the column should only accepts the values between
1-4.(it should not be more than 4 and less than 1) Is it possible in postgress?
Thanks in Advance.
I may handle it in the code level but is there is a way to do it in Database level.
You almost certainly don't mean "postgresql 9.4" in your tags - that version is VERY old.
What you are after is a "CHECK constraint".
https://www.postgresql.org/docs/15/ddl-constraints.html
You use it something like this:
CREATE TABLE mytable (
...
my_column int NOT NULL CHECK (my_column BETWEEN 1 AND 4)
...
)
For PostgreSQL at least, the check shouldn't rely on running a query, just accessing columns from the row you are inserting or updating.
I have two tables with identical structures. All columns are integers and are named "A" , "B" and "key".
I can insert from one table into another with some SQL like this:
INSERT INTO test_table_kewmfsznj
SELECT * FROM tmp_test_table_kewmfsznj_cnxtbkbq ta
But this doesn't work:
INSERT INTO test_table_kewmfsznj
SELECT * FROM tmp_test_table_kewmfsznj_cnxtbkbq ta
ON CONFLICT ("key")
DO NOTHING
My expectation was that this code would skip any row from "ta" where the key already exists in the table I'm inserting into. Instead I get this error:
ERROR: missing FROM-clause entry for table "ta"
Position: 152
Here's what I really want to do: When the key already exists in the table I'm inserting into, I want to update certain columns:
INSERT INTO test_table_kewmfsznj
SELECT * FROM tmp_test_table_kewmfsznj_cnxtbkbq ta
ON CONFLICT ("key")
DO UPDATE SET "A" = ta."A", "B" = ta."B"
Unfortunately this gives me (almost) the same error:
ERROR: missing FROM-clause entry for table "ta"
Position: 134
Can somebody explain what I am doing wrong here?
EDIT0: I tried it without upper case table names. The columns are now called "a", "b" and "key". The data remains unchanged - it's all integers.
INSERT INTO test_table_mrcvnaoia
SELECT * from tmp_test_table_mrcvnaoia_uuxkaidv ta
ON CONFLICT (key)
DO UPDATE SET a = ta.a, b = ta.b
... and now I get this error:
SQL Error [42P01]: ERROR: missing FROM-clause entry for table "ta"
Position: 129
To me, this suggests that there's something wrong with my ON CONFLICT statement, and probably not the first half of the query, but beyond that I'm out of clues. Can anybody help?
You almost had it, but you can't reference the table name, you reference EXCLUDED:
INSERT INTO test_table_mrcvnaoia
SELECT * from tmp_test_table_mrcvnaoia_uuxkaidv
ON CONFLICT (key)
DO UPDATE SET a = EXCLUDED.a, b = EXCLUDED.b;
Furthermore, to avoid errors in the future, make sure you explicitly specify the column names in the insert and select portions of your statement. They are the same for now, but that might not always be the case.
I have a UUID constraint set up as my Id field in one of my tables, however despite this (I think due to the fact that uuid_generate_v4 only creates on UUID per transaction?) when I imported a load of CSV data into my table, each row in the table was given the same UUID.
I want to be able to change this and give each row a unique UUID, however running
update monitors_nontest set id = uuid_generate_v1()
Again only produces one UUID for each row.
How can I change this command so that each row gets a different UUID?
Just a possibility. How did you actually generate the uuid? The function uuid_generate_v1() actually generates a different value each time it is called. But that is the key each time it is called. It seems if called within a sub select the Postgres optimizer may feel it can bypass the call and use cached result. Try the following.
create table uuid_gen( id1a uuid
, id1b uuid
, num1 integer
);
insert into uuid_gen(num1)
select generate_series(1,50);
update uuid_gen set id1a = uuid_generate_v1();
update uuid_gen set id1b = (select uuid_generate_v1());
select count(distinct id1a), count(distinct id1b) from uuid_gen;
Unfortunately, I could not find a fiddle processor that had the function uuid_generate_v1() available, nor uuid_generate_v4() which worked exactly the same.
I had not exactly the same problem, but something similar.
I was working with pre-Postgres13 version (so I did not have any function ready).
I had a table where I needed to insert new rows into the table while generating a new UUID(v4) for each new row.
I was looking everywhere but couldn't find anything w/o creating a function or installing extensions.
So I made it this way:
INSERT INTO monitors_nontest (id, col1, col2, col3)
SELECT uuid_in(md5(random()::text || random()::text)::cstring), mn.col1, mn.col2, mn.col3
FROM monitors_nontest mn
WHERE mn.col1 = 'some-text'
This could be adjusted for the UPDATE query. I hope it will help somebody else.
I am using Ubuntu and PostgreSql 8.4.9.
Now, for any table in my database, if I do select table_name.name from table_name, it shows a result of concatenated columns for each row, although I don't have any name column in the table. For the tables which have name column, no issue. Any idea why?
My results are like this:
select taggings.name from taggings limit 3;
---------------------------------------------------------------
(1,4,84,,,PlantCategory,soil_pref_tags,"2010-03-18 00:37:55")
(2,5,84,,,PlantCategory,soil_pref_tags,"2010-03-18 00:37:55")
(3,6,84,,,PlantCategory,soil_pref_tags,"2010-03-18 00:37:55")
(3 rows)
select name from taggings limit 3;
ERROR: column "name" does not exist
LINE 1: select name from taggings limit 3;
This is a known confusing "feature" with a bit of history. Specifically, you could refer to tuples from the table as a whole with the table name, and then appending .name would invoke the name function on them (i.e. it would be interpreted as select name(t) from t).
At some point in the PostgreSQL 9 development, Istr this was cleaned up a bit. You can still do select t from t explicitly to get the rows-as-tuples effect, but you can't apply a function in the same way. So on PostgreSQL 8.4.9, this:
create table t(id serial primary key, value text not null);
insert into t(value) values('foo');
select t.name from t;
produces the bizarre:
name
---------
(1,foo)
(1 row)
but on 9.1.1 produces:
ERROR: column t.name does not exist
LINE 1: select t.name from t;
^
as you would expect.
So, to specifically answer your question: name is a standard type in PostgreSQL (used in the catalogue for table names etc) and also some standard functions to convert things to the name type. It's not actually reserved, just the objects that exist called that, plus some historical strange syntax, made things confusing; and this has been fixed by the developers in recent versions.
According to the PostgreSQL documentation, name is a "non-reserved" keyword in PostgreSQL, SQL:2003, SQL:1999, or SQL-92.
SQL distinguishes between reserved and non-reserved key words. According to the standard, reserved key words are the only real key words; they are never allowed as identifiers. Non-reserved key words only have a special meaning in particular contexts and can be used as identifiers in other contexts. Most non-reserved key words are actually the names of built-in tables and functions specified by SQL. The concept of non-reserved key words essentially only exists to declare that some predefined meaning is attached to a word in some contexts.
The suggested fix when using keywords is:
As a general rule, if you get spurious parser errors for commands that contain any of the listed key words as an identifier you should try to quote the identifier to see if the problem goes away.
In PostgreSQL, how do I get the last id inserted into a table?
In MS SQL there is SCOPE_IDENTITY().
Please do not advise me to use something like this:
select max(id) from table
( tl;dr : goto option 3: INSERT with RETURNING )
Recall that in postgresql there is no "id" concept for tables, just sequences (which are typically but not necessarily used as default values for surrogate primary keys, with the SERIAL pseudo-type).
If you are interested in getting the id of a newly inserted row, there are several ways:
Option 1: CURRVAL(<sequence name>);.
For example:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John');
SELECT currval('persons_id_seq');
The name of the sequence must be known, it's really arbitrary; in this example we assume that the table persons has an id column created with the SERIAL pseudo-type. To avoid relying on this and to feel more clean, you can use instead pg_get_serial_sequence:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John');
SELECT currval(pg_get_serial_sequence('persons','id'));
Caveat: currval() only works after an INSERT (which has executed nextval() ), in the same session.
Option 2: LASTVAL();
This is similar to the previous, only that you don't need to specify the sequence name: it looks for the most recent modified sequence (always inside your session, same caveat as above).
Both CURRVAL and LASTVAL are totally concurrent safe. The behaviour of sequence in PG is designed so that different session will not interfere, so there is no risk of race conditions (if another session inserts another row between my INSERT and my SELECT, I still get my correct value).
However they do have a subtle potential problem. If the database has some TRIGGER (or RULE) that, on insertion into persons table, makes some extra insertions in other tables... then LASTVAL will probably give us the wrong value. The problem can even happen with CURRVAL, if the extra insertions are done intto the same persons table (this is much less usual, but the risk still exists).
Option 3: INSERT with RETURNING
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John') RETURNING id;
This is the most clean, efficient and safe way to get the id. It doesn't have any of the risks of the previous.
Drawbacks? Almost none: you might need to modify the way you call your INSERT statement (in the worst case, perhaps your API or DB layer does not expect an INSERT to return a value); it's not standard SQL (who cares); it's available since Postgresql 8.2 (Dec 2006...)
Conclusion: If you can, go for option 3. Elsewhere, prefer 1.
Note: all these methods are useless if you intend to get the last inserted id globally (not necessarily by your session). For this, you must resort to SELECT max(id) FROM table (of course, this will not read uncommitted inserts from other transactions).
Conversely, you should never use SELECT max(id) FROM table instead one of the 3 options above, to get the id just generated by your INSERT statement, because (apart from performance) this is not concurrent safe: between your INSERT and your SELECT another session might have inserted another record.
See the RETURNING clause of the INSERT statement. Basically, the INSERT doubles as a query and gives you back the value that was inserted.
Leonbloy's answer is quite complete. I would only add the special case in which one needs to get the last inserted value from within a PL/pgSQL function where OPTION 3 doesn't fit exactly.
For example, if we have the following tables:
CREATE TABLE person(
id serial,
lastname character varying (50),
firstname character varying (50),
CONSTRAINT person_pk PRIMARY KEY (id)
);
CREATE TABLE client (
id integer,
CONSTRAINT client_pk PRIMARY KEY (id),
CONSTRAINT fk_client_person FOREIGN KEY (id)
REFERENCES person (id) MATCH SIMPLE
);
If we need to insert a client record we must refer to a person record. But let's say we want to devise a PL/pgSQL function that inserts a new record into client but also takes care of inserting the new person record. For that, we must use a slight variation of leonbloy's OPTION 3:
INSERT INTO person(lastname, firstname)
VALUES (lastn, firstn)
RETURNING id INTO [new_variable];
Note that there are two INTO clauses. Therefore, the PL/pgSQL function would be defined like:
CREATE OR REPLACE FUNCTION new_client(lastn character varying, firstn character varying)
RETURNS integer AS
$BODY$
DECLARE
v_id integer;
BEGIN
-- Inserts the new person record and retrieves the last inserted id
INSERT INTO person(lastname, firstname)
VALUES (lastn, firstn)
RETURNING id INTO v_id;
-- Inserts the new client and references the inserted person
INSERT INTO client(id) VALUES (v_id);
-- Return the new id so we can use it in a select clause or return the new id into the user application
RETURN v_id;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
Now we can insert the new data using:
SELECT new_client('Smith', 'John');
or
SELECT * FROM new_client('Smith', 'John');
And we get the newly created id.
new_client
integer
----------
1
you can use RETURNING clause in INSERT statement,just like the following
wgzhao=# create table foo(id int,name text);
CREATE TABLE
wgzhao=# insert into foo values(1,'wgzhao') returning id;
id
----
1
(1 row)
INSERT 0 1
wgzhao=# insert into foo values(3,'wgzhao') returning id;
id
----
3
(1 row)
INSERT 0 1
wgzhao=# create table bar(id serial,name text);
CREATE TABLE
wgzhao=# insert into bar(name) values('wgzhao') returning id;
id
----
1
(1 row)
INSERT 0 1
wgzhao=# insert into bar(name) values('wgzhao') returning id;
id
----
2
(1 row)
INSERT 0
The other answers don't show how one might use the value(s) returned by RETURNING. Here's an example where the returned value is inserted into another table.
WITH inserted_id AS (
INSERT INTO tbl1 (col1)
VALUES ('foo') RETURNING id
)
INSERT INTO tbl2 (other_id)
VALUES ((select id from inserted_id));
See the below example
CREATE TABLE users (
-- make the "id" column a primary key; this also creates
-- a UNIQUE constraint and a b+-tree index on the column
id SERIAL PRIMARY KEY,
name TEXT,
age INT4
);
INSERT INTO users (name, age) VALUES ('Mozart', 20);
Then for getting last inserted id use this for table "user" seq column name "id"
SELECT currval(pg_get_serial_sequence('users', 'id'));
SELECT CURRVAL(pg_get_serial_sequence('my_tbl_name','id_col_name'))
You need to supply the table name and column name of course.
This will be for the current session / connection
http://www.postgresql.org/docs/8.3/static/functions-sequence.html
For the ones who need to get the all data record, you can add
returning *
to the end of your query to get the all object including the id.
You can use RETURNING id after insert query.
INSERT INTO distributors (id, name) VALUES (DEFAULT, 'ALI') RETURNING id;
and result:
id
----
1
In the above example id is auto-increment filed.
The better way is to use Insert with returning. Though there are already same answers, I just want to add, if you want to save this to a variable then you can do this
insert into my_table(name) returning id into _my_id;
Postgres has an inbuilt mechanism for the same, which in the same query returns the id or whatever you want the query to return.
here is an example. Consider you have a table created which has 2 columns column1 and column2 and you want column1 to be returned after every insert.
# create table users_table(id serial not null primary key, name character varying);
CREATE TABLE
#insert into users_table(name) VALUES ('Jon Snow') RETURNING id;
id
----
1
(1 row)
# insert into users_table(name) VALUES ('Arya Stark') RETURNING id;
id
----
2
(1 row)
Try this:
select nextval('my_seq_name'); // Returns next value
If this return 1 (or whatever is the start_value for your sequence), then reset the sequence back to the original value, passing the false flag:
select setval('my_seq_name', 1, false);
Otherwise,
select setval('my_seq_name', nextValue - 1, true);
This will restore the sequence value to the original state and "setval" will return with the sequence value you are looking for.
I had this issue with Java and Postgres.
I fixed it by updating a new Connector-J version.
postgresql-9.2-1002.jdbc4.jar
https://jdbc.postgresql.org/download.html:
Version 42.2.12
https://jdbc.postgresql.org/download/postgresql-42.2.12.jar
Based on #ooZman 's answer above, this seems to work for PostgreSQL v12 when you need to INSERT with the next value of a "sequence" (akin to auto_increment) without goofing anything up in your table(s) counter(s). (Note: I haven't tested it in more complex DB cluster configurations though...)
Psuedo Code
$insert_next_id = $return_result->query("select (setval('"your_id_seq"', (select nextval('"your_id_seq"')) - 1, true)) +1");