I am pulling some records in table A from X table.
Now, I want to select records which are not available in table A but available in table B. But at the same time, I don't want to select records available in both tables.
Moreover,if a column in table A is null but the same column in the record in table B has value, I want to take that too.
Is it possible to do something like this in one statement ?
This is a simple set based operation. Relational databases are very good in that:
CREATE TABLE a (id NUMBER);
CREATE TABLE b (id NUMBER);
INSERT INTO a VALUES (1);
INSERT INTO a VALUES (3);
INSERT INTO b VALUES (2);
INSERT INTO b VALUES (3);
SELECT id FROM b
MINUS
SELECT id FROM a;
ID
2
Related
I have two table,and they are connected by one field : B_ID of table A & id of table B.
I want to use sql to insert data to this two table.
how to write the insert sql ?
1,id in table B is auto-increment.
2,in a stupid way,I can insert data to table B first,and then select the id from table B,then add the id to table A as message_id.
You cannot insert data to multiple tables in one SQL statement. Just insert data first to B table and then table A. You could use RETURNING statement to get ID value and get rid of additional select statement between inserts.
See: https://oracle-base.com/articles/misc/dml-returning-into-clause
Have you heard about AFTER INSERT trigger? I think it is what you are looking for.
Something like this might do what you want:
CREATE OR REPLACE TRIGGER TableB_after_insert
AFTER INSERT
ON TableB
FOR EACH ROW
DECLARE
v_id int;
BEGIN
/*
* 1. Select your id from TableB
* 2. Insert data to TableA
*/
END;
/
I have two db2 tables, table one contains rows of constant data with id as one of the columns. second table contains id column which is foreign key to id column in first table and has 3 more varchar columns.
I am trying to insert rows into second table, where entry into id col is based on a where clause and the remaining columns get values from outside.
table1 has columns id, t1c1, t1c2, t1c3
table2 has columns id, t2c1, t2c2, t2c3
to insert into table2, I am trying this query:
insert into table2 values
(select id from table1 where t1c2 like 'xxx', 'abc1','abc2');
I know it is something basic I am missing here.
Please help correcting this query.
I create a table in Oracle 11g with the default value for one of the columns. Syntax is:
create table xyz(emp number,ename varchar2(100),salary number default 0);
This created successfully. For some reasons I need to create another table with same old table structure and data. So I created a new table with name abc as
create table abc as select * from xyz.
Here "abc" created successfully with same structure and data as old table xyz. But for the column "salary" in old table "xyz" default value was set to "0". But in the newly created table "abc" the default value is not set.
This is all in Oracle 11g. Please tell me the reason why the default value was not set and how we can set this using select statement.
You can specify the constraints and defaults in a CREATE TABLE AS SELECT, but the syntax is as follows
create table t1 (id number default 1 not null);
insert into t1 (id) values (2);
create table t2 (id default 1 not null)
as select * from t1;
That is, it won't inherit the constraints from the source table/select. Only the data type (length/precision/scale) is determined by the select.
The reason is that CTAS (Create table as select) does not copy any metadata from the source to the target table, namely
no primary key
no foreign keys
no grants
no indexes
...
To achieve what you want, I'd either
use dbms_metadata.get_ddl to get the complete table structure, replace the table name with the new name, execute this statement, and do an INSERT afterward to copy the data
or keep using CTAS, extract the not null constraints for the source table from user_constraints and add them to the target table afterwards
You will need to alter table abc modify (salary default 0);
new table inherits only "not null" constraint and no other constraint.
Thus you can alter the table after creating it with "create table as" command
or you can define all constraint that you need by following the
create table t1 (id number default 1 not null);
insert into t1 (id) values (2);
create table t2 as select * from t1;
This will create table t2 with not null constraint.
But for some other constraint except "not null" you should use the following syntax
create table t1 (id number default 1 unique);
insert into t1 (id) values (2);
create table t2 (id default 1 unique)
as select * from t1;
I have two Oracle questions.
How can I set the primary key of a table when the table is made up of an object type? e.g.
CREATE TABLE object_names OF object_type
I have created a Varray type,
CREATE TYPE MULTI_TAG AS VARRAY(10) OF VARCHAR(10);
but when I try to do
SELECT p.tags.count FROM pg_photos p;
I get an invalid identifier error on the "count" part. p.tags is a MULTI_TAG, how can I get the number of elements in the MULTI_TAG?
First of all I wouldn't recommend storing data in Object tables. Objects are a great programmatic tool but querying Object tables leads to complicated SQL. I would advise storing your data in a standard relationnal model and using the objects in your procedures.
Now to answer your questions:
A primary key should be immutable, so most of the time an Object type is inappropriate for a primary key. You should define a surrogate key to reference your object.
You will have to convert the varray into a table to be able to query it from SQL
For example:
SQL> CREATE TYPE MULTI_TAG AS VARRAY(10) OF VARCHAR(10);
2 /
Type created
SQL> CREATE TABLE pg_photos (ID number, tags multi_tag);
Table created
SQL> INSERT INTO pg_photos VALUES (1, multi_tag('a','b','c'));
1 row inserted
SQL> INSERT INTO pg_photos VALUES (2, multi_tag('e','f','g'));
1 row inserted
SQL> SELECT p.id, COUNT(*)
2 FROM pg_photos p
3 CROSS JOIN TABLE(p.tags)
4 GROUP BY p.id;
ID COUNT(*)
---------- ----------
1 3
2 3
1)
A primary key is a constraint, to add constrains on object tables check this link:
http://download-west.oracle.com/docs/cd/B28359_01/appdev.111/b28371/adobjdes.htm#i452285
2)
The COUNT method can't be used in a SQL statement:
REF LINK IN COMMENTS
So in my case I had to do
SELECT p.pid AS pid, count(*) AS num_tags FROM pg_photos p, TABLE(p.tags) t2 GROUP BY p.pid;
I have two tables:
create table Number( num number(5));
create table Entry(id number(3), name varchar(50));
How can I increment the num field of Number table in Oracle whenever I insert something in the Entry table?
You should use a SEQUENCE instead. The "Number" table is an inherently bad idea, because when two sessions are inserting rows concurrently, each session only sees the uncommited value in the Number table.
This is what you should do instead:
create sequence entrySeq;
create table Entry(id number(3), name varchar(50));
create trigger tr_entry before insert on Entry for each row
begin
select entrySeq.nextval into :new.number from dual;
end;
/
Do you want number.num to continually represent the number of rows iin the Entry table? If so you could just define it as a view:
create view number_view
as
select count(*) from Entry
create sequence entrySeq;
create table Entry(id number(3), name varchar(50));
insert into Entry value (entrySeq.nextval, 'MyName');
(You don't need a trigger).
A sequence returns a unique and increasing number value but Oracle doesn't guarantuee that it is gapless. When sometimes transactions are rollbacked the values of column id will contain gaps.