I'm a newbie to pgsql. I have few questionss on it:
1) I know it is possible to access columns by <schema>.<table_name>, but when I try to access columns like <db_name>.<schema>.<table_name> it throwing error like
Cross-database references are not implemented
How do I implement it?
2) We have 10+ tables and 6 of have 2000+ rows. Is it fine to maintain all of them in one database? Or should I create dbs to maintain them?
3) From above questions tables which have over 2000+ rows, for a particular process I need a few rows of data. I have created views to get those rows.
For example: a table contains details of employees, they divide into 3 types; manager, architect, and engineer. Very obvious thing this table not getting each every process... process use to read data from it...
I think there are two ways to get data SELECT * FROM emp WHERE type='manager', or I can create views for manager, architect n engineer and get data SELECT * FROM view_manager
Can you suggest any better way to do this?
4) Do views also require storage space, like tables do?
Thanx in advance.
Cross Database exists in PostGreSQL for years now. You must prefix the name of the database by the database name (and, of course, have the right to query on it). You'll come with something like this:
SELECT alias_1.col1, alias_2.col3 FROM table_1 as alias_1, database_b.table_2 as alias_2 WHERE ...
If your database is on another instance, then you'll need to use the dblink contrib.
This question doe not make sens. Please refine.
Generally, views are use to simplify the writing of other queries that reuse them. In your case, as you describe it, maybe that stored proceudre would better fits you needs.
No, expect the view definition.
1: A workaround is to open a connection to the other database, and (if using psql(1)) set that as your current connection. However, this will work only if you don't try to join tables in both databases.
1) That means it's not a feature Postgres supports. I do not know any way to create a query that runs on more than one database.
2) That's fine for one database. Single databases can contains billions of rows.
3) Don't bother creating views, the queries are simple enough anyway.
4) Views don't require space in the database except their query definition.
Related
I have a multi tennant application which will use the SILO Model to save data (each tennant will get an own database).
Because tennant names could be redundand my database are with GUIDs: MyApp_[GUID].
Now I want to save simple but neccesary information for each database like a tennant name and 3 to 5 more informations.
Is there a simple way to write and get these data?
The only way I can think of is to create a special table for this with only 1 row - but it seems a bot of wasting.
If you're looking for a simpler solution than a table per database (and having to deal with the awkward constraint that it must have exactly one row), you could
use a custom configuration parameter. You can change them with ALTER DATABASE. The downside is that you can only store strings, and that the settings might be overridden per session.
use a COMMENT on the database. The downside is that you can only store a single string per databasebase; the advantage is that it is automatically shown in many lists of databases such as psql's \l+ command
add your own columns to the pg_database system table. You should not mess with that, so it's a spectacularly bad idea even if you knew what you were doing, but in a relational model it's the closest to what you were asking for so I'd mention it for completeness.
I don't really advocate any of these solutions, although they do what you were asking for there's probably a better solution to your actual problem. It might be as simple a table of databases, possibly with a foreign key to pg_database, in an extra database shared by all tenants.
Not able to load multiple tables, getting error:
Exception in component tMysqlInput_1 (MYSQL_DynamicLoading)
java.sql.SQLException: Bad format for Timestamp 'GUINESS' in column 3
One table works fine. Basically after first iteration the second table trying to use the schema
of the first table. Please help, how to edit the component to make it
correct. Trying to load actor & country table from sakila DB mysql to
a another DB on the same server. Above image is for successful one table
dynamic loading.
you should not use tMysqlInput if output schemas differ. For this case there is no way around tJavaRow and custom code. I however cannot guess what happens in tMap, so you should provide some more details about what you want to achieve.
If all you need is to load data from one table to another without any transformations, you can do one of the following:
If your tables reside in 2 different databases on the same server, you can use a tMysqlRow and execute a query "INSERT INTO catalog.table SELECT * from catalog2.table2..". You can do some simple transformations in SQL if needed.
If your tables live in different servers, check the generic solution I suggested for a similar question here. It may need some tweaking depending on your use case, but the general idea is to replicate the functionality of INSERT INTO SELECT when the tables are not on the same server.
Is it possible to get the table structure like db2look from SQL?
Or the only way is from command line? Thus, by wrapping a external stored procedure in C I could call the db2look, but that is not what I am looking for.
Clarification added later:
I want to know which tables have the non logged option from SQL.
It is possible to create the table structure from regular SQL and the public DB2 catalog - however, it is complex and requires some deeper skills.
The metadata is available in the DB2 catalog views in the SYSCAT schema. For a regular table you would first start off by looking into the values in SYSCAT.TABLES and SYSCAT.COLUMNS. From there you would need to branch off to other views depending on what table and column options you are after, whether time-travel tables, special partitioning rules, or many other options are involved.
Serge Rielau published an article on developerWorks called Backup and restore SQL schemas for DB2 Universal Database that provides a set of stored procedures that will do exactly what you're looking for.
The article is quite old (2006) so you may need to put some time in to update the procedures to be able to handle features that were added to DB2 since the date of publication, but the procedures may work for you now and are a nice jumping off point.
Our database has about 500 tables we'd like to use in our EF model. Of those I'd be happy to start with 50 or fewer just to get our feet wet after working in plain ADO.net for years.
The problem is, our SQL server contains many thousands of other tables that exist in our database that have been created through the years and many that are dynamically generated. Believe it or not:
select count(*) from INFORMATION_SCHEMA.TABLES
73261
So that's a lot of tables. I have found that pretty much every tool I've tried to design, build or template EF models or entities either hangs or does not return a list of tables. Even SQL Server Object Explorer in VS2012 won't list the tables and instead shows the Tables folder with a little "x" over the icon. So I can't even select a subset of tables.
What options do I have for using EF? Is there a template where I can explicitly define the tables that I want to use entities for? Even with 50 tables, I don't want to hand code each one in an empty EDMX.
Using a Database / Code First approach and avoiding connecting Visual Studio to the database at all (i.e. don't create an edmx, or connect with server explorer) would allow you to do this easily. It does not give you any of the Model First advantages, but I think it sounds like your project would be better served with a Database / Code First approach anyway as:
You have an existing Model, and are not looking to push changes from your EDMX to the DB
You are looking to implement this on a subset of your database
This link has a good summation ( Code-first vs Model/Database-first ) with the caveat that in you case a Database/Code First approach does not have you pushing changes from code to the Database, so the last two bullets under code first apply less, and yours is a Database/Code First hybrid.
With 70k tables I think that any GUI is going to be tricky. When I am saying Database / Code First, I am trying to convey that you are not using the code to create / define and update your Database. Someone may be able to answer this more succinctly / accurately?
I now this is an old question. But for those who land here on a google search. The only tool I have found that actually works with thousands of tables is The Sharp Factory.
It is an ORM. Pretty simple to use. So if you are looking for an ORM that can work with a large number of tables and does not require you to write "POCOS" or "Mappings" or SQL then this is the tool.
You can find it here: The Sharp Factory
I was wondering whether it is possible to query tables by specifying their object_id instead of table names in SELECT statements.
The reason for this is that some tables are created dynamically, and their structure (and names) are not known before, and yet I would like to be able to write sprocs that are capable of querying these tables and working on their content.
I know I can create dynamic statements and execute it, but maybe there are some better ways, and I would be grateful if someone could share how to approach it.
Thanks.
You have to query sys.columns and build a dynamic query based on that.
There are no better ways: SQL isn't designed for adhoc or unknown sturctures.
I've never worked on an application in 20 years where I don't know what my data looks like. Either your data is persisted or it should be in XML or JSON or such if it's transient-