I am not so into PostgreSQL and pgAdmin 4 and I have the following doubt.
Following a screenshot of what I can see in my pgAdmin4:
As you can see it is performing this very simple query:
SELECT * FROM public."Example"
ORDER BY id ASC
The thing that I am not understanding is what is this public name in front of the Example table name. What is it?
I was trying to perform a query in this way but it is not working:
SELECT * FROM Example
ORDER BY id ASC
It give me a syntax error. I often used MySql and in MySql it is working.
I tried to replace the query in this way:
SELECT * FROM "Example"
ORDER BY id ASC
and so it is working. So it means that in PosgreSQL database the "" around the table name are mandatory?
The thing that I am not understanding is what is this public name in front of the Example table name. What is it?
As said in postgres documentation:
"By default tables (and other objects) are automatically put into a schema named "public". Every new database contains such a schema."
So it means that in PosgreSQL database the "" around the table name
are mandatory?
Not really but you need to use it if you are using reserved keywords (such as "user","name"and other)or if your table's name contains uppercase(it's your case) letters. Anyways, in this case if you can it's better change your table's name.
You should change your table name to all alphabet in lowercase then try again with
select * from example
Related
Let's say I have a table Student with just 2 columns - id bigint, name varchar(50).
I'm trying to rename it and add column in a same single query in PostgreSQL version 11.16 like below:
ALTER TABLE student
RENAME COLUMN name TO fullname,
ADD COLUMN roll_no varchar(30);
But I got this error:
Syntax error at or near "ADD"
Is it possible? If not, why?
Actually, that is not possible. I got this from the StackOverflow answer. One RENAME is possible for only one statement. Even multiple RENAME commands are also not possible. Here is the postgres manual.
I know this sounds like an "opinion" question, but I don't think it is.
Normally, I would consider not using "user" as a table name as it is a reserved word, and I would rather not bother having to deal with it when I write native SQL queries.
But I am not writing native SQL queries, but am having Symfony and the Doctrine ORM perform all the queries. And when I execute php bin/console make:user, Symfony prompts me to select the class name User which results with user as the table name. Furthermore, most of the tutorials I have read also use the name user. If using the name user is what is most common for other developers, I would rather stay consistent.
Most of the time, I don't have any issues, but every now and then, Doctrine crashes because it is querying the Postgres internal user table and not public.user. As a workaround, I tried adding * #ORM\Table(schema="public") to the User entity, but then when making migrations, it tries to duplicate the record resulting in errors. Maybe Symfony/Doctrine needs to be configured somewhere as using the public schema?
Thanks
Since my question was "Should the table name “user” be used in a Symfony project?", the following doesn't answer the question, but I am still posting it should it be helpful for others. Perhaps I will change the title to "How to use the table name “user” in a Doctrine project?", but not sure whether doing so is kosher.
I've since discovered other's experiencing issues resulting from this topic:
https://github.com/doctrine/dbal/issues/1222
https://github.com/symfony/maker-bundle/pull/545
Also found the following at doctrine-adding-mapping:
Be careful not to use reserved SQL keywords as your table or column
names (e.g. GROUP or USER). See Doctrine’s Reserved SQL keywords
documentation for details on how to escape these. Or, change the table
name with #ORM\Table(name="groups") above the class or configure the
column name with the name="group_name" option.
Which directed me to quoting-reserved-words which directed me to escape the name using ticks.
* #ORM\Table(name="`user`")
There is no table user in PostgreSQL.
Tutorials that use user as a table name are not trustworthy. However, if you consistently use double quotes, there should be no problem. Since you claim to have problems with native queries, you might have forgotten that occasionally.
One possible source of confusion is that there is a function named user in PostgreSQL. So if you use user in a context where a function is possible, you'll get a function call. If you use it with schema qualification, you will get an error that there is no such object. Otherwise, you will get a syntax error:
test=> SELECT user;
user
---------
laurenz
(1 row)
test=> SELECT * FROM user;
user
---------
laurenz
(1 row)
test=> TABLE user;
ERROR: syntax error at or near "user"
LINE 1: TABLE user;
^
test=> SELECT * FROM public.user;
ERROR: relation "public.user" does not exist
LINE 1: SELECT * FROM public.user;
^
Following the blog of Rob Conery I have set of unique IDs across the tables of my Postgres DB.
Now, using these unique IDs, is there a way to query a row on the DB without knowing what table it is in? Or can those tables be indexed such that if the row is not available on the current table, I just increase the index and I can query to the next table?
In short - if you did not prepared for that - then no. You can prepare for that by generating your own uuid. Please look here. For instance PG has uuid that preserve order. Also uuid v5 has something like namespaces. So you can build hierarchy. However that is done by hashing namespace, and I don't know tool to do opposite inside PG.
If you know all possible tables in advance you could prepare a query that simply UNIONs a search with a tagged type over all tables. In case of two tables named comments and news you could do something like:
PREPARE type_of_id(uuid) AS
SELECT id, 'comments' AS type
FROM comments
WHERE id = $1
UNION
SELECT id, 'news' AS type
FROM news
WHERE id = $1;
EXECUTE type_of_id('8ecf6bb1-02d1-4c04-8875-f1da62b7f720');
Automatically generating this could probably be done by querying pg_catalog.pg_tables and generating the relevant query on the fly.
I've noticed that while I can use %dictionary.compiledclass to get a table with schema names and table names, which allow querying for their existence, I cannot do the same for columns. I have yet to find the command that allows verifying whether a column exists or not, or retrieving numerous column names using LIKE "prefix%".
Is there even such a thing? Or an alternative?
You can use %Dictionary.CompiledProperty table and SqlFieldName column of that table.
For example to find out tables that have column 'ColumnName' you can use this query:
select parent->SqlTableName
from %dictionary.compiledproperty
where SqlFieldName='ColumnName'
Execute this Query :
select * from %dictionary.compiledproperty Where parent='TableName' and SqlFieldName='ColumnName'
Check Row Count value ,0 not exist
I have an issue with psql. I am trying to select the records from a table but psql acts like the table doesnt exist. I have tried finding it and found that it resides in the 'public' schema. I have tried selecting from this table like so:
highways=# SELECT * FROM public.CLUSTER_128000M;
This does not work stating the following:
ERROR: relation 'public.CLUSTER_128000M' does not exist
I know that it definetly exists and that it is definetly in the 'public' schema so how can I perform a select statement on it?
Edit:
This was caused by useing FME to create my tables. As a result FME used " marks on the table names making them case sensitive. To reverse this see the comments below.
This issue was caused by the third party software FME using quotes around the names of the tables at time of creation. The solution to make the tables useable again was to use the following command:
ALTER TABLE "SOME_NAME" RENAME TO some_name