Using variables in Oracle script

Question

There is a complex query which generates a report. The query has several sub queries that generate 3-columns table for different products. Each sub query returns one row. All returned rows then need to be united. But there is one requirement. If there are no result rows for a sub query we need to include the corresponding product to the final report anyway, but specify that Trades_Count is equal to zero.

I can achieve this using set of variables. The following code will work perfectly in MS SQL Server:

DECLARE @PRODUCT_NAME_1 nvarchar(100);
DECLARE @OFFER_VALID_DATE_1 datetime;
DECLARE @TRADES_COUNT_1 int;

DECLARE @PRODUCT_NAME_2 nvarchar(100);
DECLARE @OFFER_VALID_DATE_2 datetime;
DECLARE @TRADES_COUNT_2 int;

--Product 1 
select @PRODUCT_NAME_1 = PRODUCT_NAME, @OFFER_VALID_DATE_1 = MAX(EXPIRY_DATE), @TRADES_COUNT_1 = COUNT(DEAL_NUMBER)
from (
        --Data extractions with several joins goes here....

) as TempTable1
GROUP BY PRODUCT_NAME


--Product 2
select @PRODUCT_NAME_2 = PRODUCT_NAME, @OFFER_VALID_DATE_2 = MAX(EXPIRY_DATE), @TRADES_COUNT_2 = COUNT(DEAL_NUMBER)
from (
        --Data extractions with several joins goes here....
) as TempTable2
GROUP BY PRODUCT_NAME


SELECT ISNULL(@PRODUCT_NAME_1,'Product 1') AS PRODUCT_NAME, @OFFER_VALID_DATE_1 AS MAX_MATURITY, ISNULL(@TRADES_COUNT_1,0)
UNION
(
SELECT ISNULL(@PRODUCT_NAME_2,'Product 2') AS PRODUCT_NAME, @OFFER_VALID_DATE_2 AS MAX_MATURITY, ISNULL(@TRADES_COUNT_2,0)
)

I think that I haven’t used anything T-SQL specific, but pure ANSI-SQL (I’m not 100% sure though).

So this is not working in Oracle.

First of all it requires having only one DECLARE keyword. Then it forces me using Begin … End execution scope. Then it doesn’t allow me to assign variables like I do (see example above) – I need to use “Select INTO” statement instead. After all calculations are done it doesn’t allow me selecting values from local variables. Heck.

Does anyone know how to make it work in Oracle?

Thanks!

Answer 1

PL/SQL is different than t-sql, I did a change with some comments for you, but definitely look at the links from Andy. This was ran in oracle's free SQL Developer (which also has a "Translation Scratch Handler (tools>Migration>Translation Scratch Handler) that may be of use.

--this creates a refcursor to allow us to simply print the results
var refc refcursor
/

declare --here we declare our variables
    product_name_1 varchar2(15) ;
    offer_valid_date_1 date ;
    trade_count_1 number ;
    product_name_2 varchar2(15) ;
    offer_valid_date_2 date ;
    trade_count_2 number ;    
begin
    begin --this creates a block so we may handle any exceptions just to this
          select PRODUCT_NAME,    MAX(EXPIRY_DATE),    COUNT(DEAL_NUMBER)
            into product_name_1 , offer_valid_date_1 , trade_count_1
            --in oracle you select INTO, not var=COL
        from (
                --Data extractions with several joins goes here....
                select 
                    123 PRODUCT_NAME,    
                    sysdate EXPIRY_DATE,    
                    5 DEAL_NUMBER
                from dual --this is a 'fake' table to generate some data for testing

        )  TempTable1 --drop the "as"
        GROUP BY PRODUCT_NAME ;
    exception --if not data is found, then this error is thrown
              --if multiple values are thrown an error will also be thrown (not caught here)
    when no_data_found then
        product_name_1 := null ; --note, to do a var = , we use "var := value;"
        offer_valid_date_1 := null;
        trade_count_1 := null;
    end ;
    begin
          select PRODUCT_NAME,    MAX(EXPIRY_DATE),    COUNT(DEAL_NUMBER)
            into product_name_2 , offer_valid_date_2 , trade_count_2
            --in oracle you select INTO, not var=COL
        from (
                --Data extractions with several joins goes here....
                select 555 PRODUCT_NAME,    sysdate EXPIRY_DATE,    6 DEAL_NUMBER
                from dual

        )  TempTable2 -- drop the "as"
        GROUP BY PRODUCT_NAME ;
    exception --if not data is found, then this error is thrown
              --if multiple values are thrown an error will also be thrown (not caught here)
    when no_data_found then
        product_name_2 := null ;
        offer_valid_date_2 := null;
        trade_count_2 := null;
    end ;

    open :refc for  --you cannot just have a select statement, you must "open" a cursor for it    
    --oracle IsNull is NVL (or NVL2 or you can do a case or decode...)
    SELECT nvl(PRODUCT_NAME_1,'Product 1') AS PRODUCT_NAME
          , OFFER_VALID_DATE_1 AS MAX_MATURITY
          , nvl(TRADE_COUNT_1,0)
      FROM DUAL --you also must have a table, DUAL is an oracle table for this tasks
        UNION
   SELECT nvl(PRODUCT_NAME_2,'Product 2') AS PRODUCT_NAME
          , OFFER_VALID_DATE_2 AS MAX_MATURITY
          , nvl(TRADE_COUNT_2,0)
    FROM DUAL;

end ;
/

--now print the results, if you did this in a proc you would simple have this as an output
print refc;

-------------
PRODUCT_NAME MAX_MATURITY              NVL(:B1,0)             
-------------------------------------- ---------------------- 
123          18.FEB.2011 08:43         1                      
555          18.FEB.2011 08:43         1                      

Oracle concepts used here: Dual Table , NVL, Variables, pl/sql Exception

and look at this http://www.dba-oracle.com/t_convent_sql_server_tsql_oracle_plsql.htm

Answer 2

PL/SQL formats procedural blocks differently than T-SQL.

You'll want to use the following structure:

DECLARE
    astring varchar2(1000);
    anumber number;

BEGIN
   my SQL code here...
END;

You don't use the @ either in PL/SQL. Just use variables names directly.