You know how we could use:
dateStamp DATE DEFAULT sysdate
to assign a default value to a column in table_x. What if I want to assign a default function? Can I do that?
The function will have some values from "table_params" to run some formula including a column named : "base" in table_x.
I could possibly write a cursor to loop through and run an update statement, but I was just curious if this is possible.
thanks in advance.
From Oracle documentation:
Restriction on Default Column Values
A DEFAULT expression cannot contain references to PL/SQL functions or to other columns, the
pseudocolumns CURRVAL, NEXTVAL, LEVEL, PRIOR, and ROWNUM, or date
constants that are not fully specified.
Either use a trigger (as was already mentioned) or run an UPDATE statement after your INSERT statement(s) (shouldn't be a problem if you keep your DML in PL/SQL).
You can write an INSERT trigger for the table that calls the function you want.
Related
I'm running Apex 19.2 and I would like to create a classical or interactive report based on dynamic query.
The query I'm using is not known at design time. It depends on an page item value.
-- So I have a function that generates the SQL as follows
GetSQLQuery(:P1_MyItem);
This function may return something like
select Field1 from Table1
or
Select field1,field2 from Table1 inner join Table2 on ...
So it's not a sql query always with the same number of columns. It's completely variable.
I tried using PL/SQL function Body returning SQL Query but it seems like Apex needs to parse the query at design time.
Has anyone an idea how to solve that please ?
Cheers,
Thanks.
Enable the Use Generic Column Names option, as Koen said.
Then set Generic Column Count to the upper bound of the number of columns the query might return.
If you need dynamic column headers too, go to the region attributes and set Type (under Heading) to the appropriate value. PL/SQL Function Body is the most flexible and powerful option, but it's also the most work. Just make sure you return the correct number of headings as per the query.
I am very new to oracle's sql developer (since we've studied mysql) as well as in programming. I've searched in this website the answer to my question but I really can't understand the solutions provided.
What I want is to return the ID generated after inserting an object from java into the database. I'm using mybatis and oracle 10g database. I've already created the table and its columns.
Here's my code for the mapper
<insert id="addUser" parameterType="User" statementType="CALLABLE">
{ CALL addUserSP(
#{user.surname, javaType=String, jdbcType=VARCHAR, mode=IN},
#{user.firstName, javaType=String, jdbcType=VARCHAR, mode=IN},
#{userId, javaType=Integer, jdbcType=NUMBER, mode=OUT}
)}
</insert>
Here's my stored procedure (and I've already create a package named 'CREATEUSER')
PROCEDURE ADDUSERSP
( surname IN VARCHAR2,
firstName IN VARCHAR2,
userId OUT NUMBER
) AS
BEGIN
INSERT INTO users("surname", "first_name")
VALUES (surname, firstName);
RETURNING user_id INTO userId;
END ADDUSERSP;
According to what I've found here, it seems that I need to create a trigger(?) and sequence(?) to make the user_id auto increment whenever I add new data into the table. However, I have no idea how to do it.
Here are my questions:
Is my stored procedure right? Are the codes incomplete? I mean, I have not declared the package in the mapper and I've seen that it is needed (?), something like this { CALL [CreateUser].[addUserSP]( blah blah.... Should I write a sequence and trigger or there is an easy way to make the primary key user_id to be auto incremented? Kindly also check the syntax. I have a lot of problems in syntax.
Thank you so much!
To emulate MySQL AUTO_INCREMENT in Oracle, that pattern (as you found) does use a SEQUENCE object and a BEFORE INSERT trigger.
As a demonstration, something like this for the sequence object:
CREATE SEQUENCE myseq START WITH 1 INCREMENT BY 1 ;
And something like this for the before insert trigger:
CREATE TRIGGER users_bi
BEFORE INSERT ON users
FOR EACH ROW
BEGIN
IF :NEW.id IS NULL THEN
SELECT myseq.NEXTVAL INTO :NEW.id FROM DUAL;
END IF;
END
As far as the procedure, I'm not a big fan of extra PL/SQL blocks that wrap a SQL INSERT statement.
It looks like you have an extra semicolon, before RETURNING. That clause is part of the INSERT statement, not a separate statement.
One big gotcha to be aware of is that SQL statements within a PL/SQL block can reference both columns and PL/SQL variables. When variables have the same names as columns, you will likely encounter behavior you didn't expect.
Typically PL/SQL author use a naming convention for variables that reduces the likelihood of name collisions. We frequently see variables with names like v_surname. (Personally, I use a slightly different convention, but the variable names "look like" variable names, not column references. And I don't name columns following the pattern I use for variables.)
The double quotes around the identifiers are acceptable, but this does make the identifiers case sensitive. When identifiers aren't enclosed in double quotes, Oracle treats them as if they were UPPER CASE. Just make sure that your table was defined with lower case column names.
Is it necessary to use GROUP BY while you use an aggregate function with column in Oracle?
In MySQL, if I don't use it's working fine, but in Oracle, it gives me an error.
It's necessary if you select at least one column without an aggregate function.
So, this will work:
select sum(col_1), avg(col_2) from table_1;
while this wont:
select sum(col_1), avg(col_2), col_3 from table_1;
You should always use GROUP BY when using aggregate functions. Not using GROUP BY is a non-standard SQL extension allowed by MySQL.
RANT
IMHO, this extension is brain-dead, outright dangerous and should never be used at all because MySQL returns values for a random row for the non-aggregated columns.
END_OF_RANT
I read somewhere that 99% of time you don't need to use a cursor.
But I can't think of any other way beside using a cursor in this following situation.
Select t.flag
From Dual t;
Let's say this return 4 rows of either 'Y' or 'N'. I want the procedure to trigger something if it finds 'Y'. I usually declare a cursor and loop until %NOTFOUND. Please tell me if there is a better way.
Also, if you have any idea, when is the best time to use a cursor?
EDIT: Instead of inserting the flags, what if I want to do "If 'Y' then trigger something"?
Your case definitely falls into the 99%.
You can easily do the conditional insert using insert into ... select.... It's just a matter or making a select that returns the result that you want to insert.
If you want to insert one record for each 'Y' then use a query with where flag = 'Y'. If you only want to insert a single record depending on whether there are at least one 'Y', then you can add distinct to the query.
A cursor is useful when you make something more complicated. I for example use a cursor when need to insert or update records in one table, and also for each record insert or update one or more records into several other tables.
Something like this:
INSERT INTO TBL_FLAG (col)
SELECT ID FROM Dual where flag = 'Y'
You will usually see a performance gain when using set based instead of procedural operations because most modern DBMS are setup to perform set based operations. You can read more here.
well the example doesnt quite make sense..
but you can always write an insert as select statement instead of what i think you are describing
Cursors are best to use when an column value form one table will be used repeatedly in multiple queries on different tables.
Suppose the values of id_test column are fetched from MY_TEST_TBL using a cursor CUR_TEST. Now this id_test column is a foreign key in MY_TEST_TBL. If we want to use id_test to insert or update any rows in table A_TBL,B_TBL and C_TBL, then in this case it's best to use cursors instead of using complex queries.
Hope this might help to understand the purpose of cursors
How to set a conditional DEFAULT value to a column in oracle without using triggers?
I want to achieve following needs:
If "flag1"=1 then Default value to column Newfield must be "4".
If "flag1"=2 then Default value to column Newfield must be "5".
That's what triggers are for. Use them.
A column DEFAULT is not allowed to reference another column, so this is not possible.
You could perhaps just let the default remain as NULL, and then have a view to adjust it like:
create view mytable_view as
select flag1, nvl(newfield, case flag1 when 1 then 4
when 2 then 5
end) as newfield
from mytable;
If column Newfield does not need to be updateable, then you could simply implement it in a view, as Tony showed, or in 11g you could make it a virtual column.
If 'flag' is something session (or statement) level then SYS_CONTEXT may be a way through. Possibly a BEFORE STATEMENT trigger if the issue is avoiding a context switch for every row inserted