I'm experiencing some difficulties with foreign key constraints. I have a table 'ADDR', whose FK constraints are:
I'm writing a UDF on Hive to analyze constraints for a target table, but I don't have any clue how to implement this.
I tried below sql script to analyze constraints FK4_ADDR, but it didn't returned empty because column CTRY_CD was also a foreign key referencing table CTRY_PSTL and CTRY. So is there any other ways to check FK integrity? Any help on this would be greatly appreciated!
select
distinct
SRC_SYS_CD,CTRY_CD,CTRY_SB_DVSN_CD
from user.ADDR t
where t.src_sys_cd='123'
minus
select
distinct
SRC_SYS_CD,CTRY_CD,CTRY_SB_DVSN_CD
from user.CTRY_SB_DVSN t1
where t1.src_sys_cd='123'
Related
I am new to Hive and have some problems. I try to find a answer here and other sites but with no luck... I also tried many different querys that come to my mind, also without success.
I have my source table and i want to create new table like this.
Were:
id would be number of distinct counties as auto increment numbers and primary key
counties as distinct names of counties (from source table)
You could follow this approach.
A CTAS(Create Table As Select)
with your example this CTAS could work
CREATE TABLE t_county
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE AS
WITH t AS(
SELECT DISTINCT county, ROW_NUMBER() OVER() AS id
FROM counties)
SELECT id, county
FROM t;
You cannot have primary key or foreign keys on Hive as you have primary key on RBDMSs like Oracle or MySql because Hive is schema on read instead of schema on write like Oracle so you cannot implement constraints of any kind on Hive.
I can not give you the exact answer because of it suppose to you must try to do it by yourself and then if you have a problem or a doubt come here and tell us. But, what i can tell you is that you can use the insertstatement to create a new table using data from another table, I.E:
create table CARS (name string);
insert table CARS select x, y from TABLE_2;
You can also use the overwrite statement if you desire to delete all the existing data that you have inside that table (CARS).
So, the operation will be
CREATE TABLE ==> INSERT OPERATION (OVERWRITE?) + QUERY OPERATION
Hive is not an RDBMS database, so there is no concept of primary key or foreign key.
But you can add auto increment column in Hive. Please try as:
Create table new_table as
select reflect("java.util.UUID", "randomUUID") id, countries from my_source_table;
I am working on this assignment question and it is asking me:
To create a table called (TEMP_CUST) from an existing table Customers
View the content and constraints of TEMP_CUST table
What I have done so far is I have created my table, didn't add any constraints to the table TEMP_CUST and viewed the table using the DESC command.
Here is the code for table creation
CREATE TABLE TEMP_CUST
AS
(SELECT
CUSTOMER#, LASTNAME,
FIRSTNAME, ADDRESS, CITY,
STATE, ZIP, REFERRED,
REGION, EMAIL
FROM
CUSTOMERS);
DESC TEMP_CUST;
Now that I have done that I want to view the constraints of the table. I have used this command but am not sure if it is correct.
SELECT *
FROM USER_CONSTRAINTS
WHERE TABLE_NAME = 'TEMP_CUST';
i have used this command, but not sure if it is correct.
You haven't said why you don't think it's correct so we have to guess the reason for your doubt. Perhaps it's because the set of constraints you get is smaller than the set of constraints for the original CUSTOMERS table?
That is correct. When we use CREATE TABLE ... AS SELECT the statement creates a new table with the projection, column names and datatypes of the original tables (assuming a vanilla SELECT clause) and the data (determined by the WHERE clause, if any). However, the only constraints which are created are NOT NULL constraints on the primary key column(s) and any other mandatory columns. The new table does not have primary key, foreign key or check constraints. We have to create these explicitly.
Hence, this query ...
SELECT * FROM USER_CONSTRAINTS
WHERE TABLE_NAME = 'TEMP_CUST';
... might return fewer constraints than you were expecting.
I want to know if there is some specific way to obtain a table-level check constraint in Oracle and in PostgreSQL.
I can obtain all the check constraints in a table, but I want to obtain only this specific check constraint, I don't know if there is any specific query.
Thanks!
In PostgreSQL there is a System Catalog pg_constraint.
The catalog pg_constraint stores check, primary key, unique, foreign
key, and exclusion constraints on tables. (Column constraints are not
treated specially. Every column constraint is equivalent to some table
constraint.) Not-null constraints are represented in the pg_attribute
catalog, not here.
User-defined constraint triggers (created with CREATE CONSTRAINT
TRIGGER) also give rise to an entry in this table.
Check constraints on domains are stored here, too.
SELECT
*
FROM
pg_constraint
WHERE
contype = 'c' AND -- check constraint
conrelid != 0 AND -- table constraint
conname = 'my_check';
The contype column contains the constraint type, c is for check constraint.
The conrelid column contains the oid of the table this constraint is on, 0 if not a table constraint.
For Oracle basic view is ALL_CONSTRAINTS
Query, to obtain specific constraint in specific table:
SELECT *
FROM all_constraints
WHERE constraint_name LIKE upper('%&your_costraint%')
AND table_name LIKE upper('%&your_table%');
Can we use select statement when we declare a check constraint
create table category
(id_category number primary key,
category varcahr2(100) check (category in (select * from table1))
thank you
No, you can't.
I'm not sure that I understand what you are trying to accomplish. If you are trying to verify that the category exists in table1, assuming that category is the primary key of table1, you'd want a foreign key constraint not a check constraint. It would seem very odd, though, for there to be a category table where the category referenced a different parent table (presumably the category table defines the valid categories). Perhaps you want to define a unique constraint to ensure that there aren't duplicate category values in the table. Perhaps you're trying to do something else-- explaining the business problem will help us understand the proper way to model the issue.
I'm currenly developing on Oracle. I have several tables for which I defined FOREIGN KEY constraints. I have already read this SQL Server-oriented and this MySQL-oriented questions but I could find none about Oracle.
So the question is always the same: in order to optimize query performance, for those columns for which I create a FOREIGN KEY constraint, do I also have to create an explicit secondary index? Doesn't Oracle automatically create an index on FOREIGN KEYed columns to boost performances during JOINs?
I usually perform queries in which the WHERE clause compare against those columns.
No, Oracle doesn't automatically create indexes on foreign key columns, even though in 99% of cases you probably should. Apart from helping with queries, the index also improves the performance of delete statements on the parent table.