I've got PostgreSQL DB with multiple schemas and tables in that schemas. Every row in table have PRIMARY UUID like "Ref_Key" => "41bf3b1e-91f0-491c-a6bd-c48a17e7c252"
Is it possible to find row only by it UUID, without specifying schema and table?
No, that is not possible. You can only query tables that explicitly appear in the FROM clause of a SELECT statement.
Related
I have create a redshift cluster and created a db inside.
My schema is new_schema
I have created 2 tables inside two tables inside table1, table2
My Question.
I want to list the datatypes of table1
I need to change the datatype of description which is inside the table1 which is of VARCHAR to TEXT
I have tried to list the datatypes of table1 with below query but nothing listing
SELECT * FROM PG_TABLE_DEF WHERE schemaname = 'new_schema';
A few possibilities as to why you are not seeing the expected results. Most likely is that new_schema isn't in your search_path. Pg_table_info only return info for tables in your search_path - see: https://docs.aws.amazon.com/redshift/latest/dg/r_PG_TABLE_DEF.html
Another possibility is that the tables have no data rows (no blocks assigned) and this can lead to incomplete info from some system tables.
Another possibility is that the tables were not committed by the creating session and being checked by a different session. Since you say that you are creating a new db this comes to mind.
Are the tables visible in svv_table_info?
Also the premise of changing varchar to text is a bit off. From https://docs.aws.amazon.com/redshift/latest/dg/r_Character_types.html#r_Character_types-text-and-bpchar-types
You can create an Amazon Redshift table with a TEXT column, but it is
converted to a VARCHAR(256) column that accepts variable-length values
with a maximum of 256 characters.
So it seems like the objective you are trying to achieve is a bit off.
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 was wondering, if it is possible to have two temp tables with the same name in two separate queries without them conflicting when called upon later in the queries.
Query 1: Create Temp Table Tmp1 as ...
Query 2: Create Temp Table Tmp1 as ...
Query 1: Do something with Tmp1 ...
I am wondering if postgresql distinguishes between those two tables, maybe through addressing them as Query1.Tmp1 and Query2.Tmp1
Each connection to the database gets its own special temporary schema name, and temp tables are created in that schema. So there will not be any conflict between concurrent queries from separate connections, even if the tables have the same names. https://dba.stackexchange.com/a/5237 for more info
The PostgreSQL docs for creating tables states:
Temporary tables exist in a special schema, so a schema name cannot be given when creating a temporary table.
How to get exported keys (database metadata).Even though redshift does not support foreign keys and primary keys I am able to see them in system tables.
The problem here is in the system table the multiple columns of a foreign key exist as an array in one column(though redshift doesn't support arrays). Is it possible to extract them in one query.
Use table_constraints table:
SELECT * FROM information_schema.table_constraints;
My database has severals table with some column type 'money'. I would like to alter all these columns (in different tables) in a single statement rather than change type column by column, to avoid omissions.
You'll have to repeat the altering query for every column.
You might want to create a program code to do that for you. You know, with loops.
In order for the database to alter all the tables atomically you should enclose all the altering queries in a transaction (PostgreSQL supports transactional DDL).