How to update multiple tables in single query in OrientDb
I have to update two tables at one short
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I have two tables, studentrecordupdated and studentrecordlegacy, with student record legacy being in the legacy schema.
Both the forms have the same data, only difference being that the studentrecordlegacy table has record forms which are not in the studentrecordupdated table. I am joining these two tables on studentid.
How do I don't a rank over partition by using both tables (some of the records in the legacy table are more recent than in the updated table)?
I'm trying to run the same query over multiple tables in my Postgres database, that all have the same schema.
This question: Select from multiple tables without a join?
shows that this is possible, however they are hard-coding the set of tables.
I have another query that returns the five specific tables I would like my main query to run on. How can I go about using the result of this with the UNION approach?
In short, I want my query to see the five specific tables (determined by the outcome of another query) as one large table when it runs the query.
I understand that in many cases similar to my scenario you'd simply just want to merge the tables. I can not do this.
One way of doing this that may satisfy your constraints is using table inheritance. In short, you will need to create a parent table with the same schema, and for each child you want to query you must ALTER that_table INHERIT parent_table. Any queries against the parent table will query all of the child tables. If you need to query different tables in different circumstances, I think the best way would be to add a column named type or some such, and query only certain values of that table.
I have to retrive the data from two tables,
Here are my two tables in Cassandra DataBase.
employee is keyspace,
Two tables:
emp:- "eno" is primay key,"username","password"
Dept:-"dno" is primary key ,"eno","dname"
Now i want to retrieve the data from two tables, e.g. eno,username,password,dno,dname.
How can i retrieve data from two tables?
How can i retrieve data from two tables?
You can't do it in one query if that is what you are asking. That means that you have to carry out two queries and let your application simulate a join, or the other option, denormalize your data so it is in one table.
As for actually carrying out the query there are bundles of APIs that can retrieve data from Cassandra.
Assuming your column families are emp and Dept you can do querying using the cli:
$ ./cassandra-cli -host localhost -port 9160
$ [default#unknown] USE employee
# single row (collection of columns)
$ [default#employee] GET emp['eno']['username']['password'] as ascii;
# 10 rows for emp column family (aka table)
$ [default#employee] LIST emp limit 10;
Check the documentation for Cassandra 0.7 for using the CLI.
Can i add multiple columns to a table in a single query execution, using alter table?
No,you can't add multiple columns in single query execution. SQLite supports a limited subset of ALTER TABLE.therefore you have to add them one by one.
see documentation at sqlite
I store data in table named by month,such as data201201,data201202 and so on,table is created in the first day of month,all tables have same struct.I design this because each month ten million rows increase and I have only sqlserver standard version so Partition table can not be used.
Before use entity framework,i used sql string to query data,so I can change tablename in sql string by query condition.
Is these any way that I can query related table in Entity Framework?
I have two idea:
1.another table design that can support such big data and minor cost?
2.Intercept ef's query and change table name by query condition,and continue this query,but how and where i can do so?