Order of Where clause

Hello GURUs
I have doubt about following. Please can all help me.
1. Does the order of table in from clause make difference. what should be the order. . largest to snmallest.
2. Does where clause order make difference. also left side to right side of equality comaprision. table row column on left and table column with less row on right.?
3. in USE_NL order of table make difference or not.? which one should be first one with less row or one with more rows. ?
4. Somtimes i have seen that USE_NL(table name) with only one table. in what condition that will be used. Larger or the smaller and then will the where clause make difference on that with USE_NL HINT.?
Message was edited by:
devmiral

Ok, because you insist :-)
I think you shouldn't care that much about these subjects, really. Oracle has an excellent cost based optimizer (cbo) that does all the work for you. It decides which predicate to apply first, the order of the tables and much more. But, and this is an important but, the cbo must have recent statistics of all the objects involved in your queries. So make sure you analyze regularly or use monitoring to stay up to date.
Applying hints like USE_NL is like saying: "I know way better than the cost based optimizer how to get the results quicker, so you should always use this access path".
Most of the time, however, something else is wrong, and by applying some hints you may (temporarily) fix the symptoms of your problem, but you are not addressing the root cause. So in case you feel the need to apply such a hint, please don't and start investigating what is really causing your problems.
Hope this helps.
Regards,
Rob.

Similar Messages

Sql order in where clause...

i want to ask about
how oracle deal with the order of where cluase
as in select * from where tname = 'EMP'
and tabtype = 'TABLE'
oracle strat from down (tabtype) or from up (tname)
and there is difference between this order
if the where clause contains (and) or (or)
i always need to know this thing but no place i found say about it in strait way..
thanks..
null

I am sorry for the late reply.
I guess that ORDER doesn't matter in the WHERE clause. We should take 2 cases:
1) Say, in a WHERE clause, U have a limiting condition on one of the indexed field of the table, then definitely that will be executed first and the result set will be passed to the other conditions.
2) Say, in the WHERE clause, U don't have any indexed field then ORACLE will go for cost based execution. In this case, it will first go to the column, for which the SELECTIVITY is the highest ( ORACLE does so internally ) and then the result set is passed to the other conditions.
Hope this helps.
Correct me, if I am wrong.

Order in where clause - SQL statement

Hi,
The order of the fields in Where clause in OpenSQL statements is important to get the right index?
Select a b c from t1
where
d = p_d and
e = p_e
Or
Select a b c from t1
where
e = p_e and
d = p_d
Index:
columns e and d.
Thanks !

HI,
Both will give you the same result.. but it is always good to pass the sequence as in the table.. the performance will be good when you follow the sequece of occurance of the fields.
Thanks
Mahesh

SQL: order of WHERE clauses important for performance?

I wonder if the order of the WHERE clauses does affect performance or if the database optimize each query so that the order is irrelevant? Example: is
SELECT *
FROM Table1
WHERE (fast condition check)
AND (slow condition check)
faster than
SELECT *
FROM Table1
WHERE (slow condition check)
AND (fast condition check)
because the first condition check might be false and therefore the second is not executed? (Some kind of Java if (fast && slow) is faster than if (slow && fast) ?)

It depends on how sophisticated the database optimizer is. IBM's DB2/UDB will completely rewrite the syntax of SQL as part of optimization and does not care what the order of the where clause is. Oracle actually has two optimizers RULE and COST. The RULE based optimizer is affected by the order of the where clause, COST is not (RULE is no longer available in the newest version of Oracle, Oracle 10g).

Plz guide - ordering in where clause

This is in general ..
when we write query we will have 2 or more tables in from clause
what should be first in order to get optimum performance.
1. Joins of tables
2. filtering clauses eg. table.abc = 20
Plz help.
Thanx in advance.

in my own i have the practice of ordering it by according to the first declaration of tables/views in the FROM clause. e.g.
Select order.order_num,
         customer.customer_name,
         items.item_description,
         orders.quantity
    From orders,
         customers,
         items
   Where order.customer_id         = customers.customer_id
     and customers.customer_active = 'Y'
     and order.item_id             = items.item_id
     and items.item_active         = 'Y'

Where clause priority in Select Query

Hi All,
I have one doubt, Pls clarify
SELECT empno, ename, sal, comm
FROM emp E, dept D -- (deptno is pk for DEPT)
WHERE D.deptno = E.deptno
AND E.sal >= 3000
In WHERE clause which one will execute first (right to left or left to right
OR[b] First join conditions then after filter conditions or vice versa)
D.deptno = E.deptno
OR
E.sal >= 3000
(this is the example tables)
Because I have large volume of data with 5 tables with joins
so, pls. kindly give me the sugession for where clause.
Thanks
Naresh

It depends, the order the where clause is written in makes no difference to how the statement is processed.
In the section on Developing Efficient SQL Statements in the Performance Tuning Guide changing the order of statements in the where clause is notably missing.
There is more information in the Understanding Joins section of the same manual.

Why I cannot use RowID in where clause but can use it in order by clause

I am on SQL Server 2008.
1. If I use
SELECT (ROW_NUMBER() over
(order by ImportId, ScenarioId, SiteID, AssetID, LocalSKUID, WEEKID, MonthID)) RowID, *
FROM [JnJ_Version1].[dbo].[td_Production_Week]
order by RowID
Statement works
But
2. If I use
SELECT (ROW_NUMBER() over
(order by ImportId, ScenarioId, SiteID, AssetID, LocalSKUID, WEEKID, MonthID)) RowID, *
FROM [JnJ_Version1].[dbo].[td_Production_Week]
  where RowID > 10000
I get error, RowID is an invalid column Name why? How to correct query 2.

This is due to the logical evaluation order of a SELECT statement. Logically, a SELECT statement is computed in the order:
FROM (which includes JOIN)
WHERE
GROUP BY
HAVING
SELECT
ORDER BY
OFFSET
Thus, you can use what is defined in the SELECT list in the ORDER BY clause, but not in the WHERE clause.
In the case of row_number(), this has immediate repurcussions. row_number() is computed from the rows as they arrive the SELECT clause, and if you then you would filter on the value in the WHERE clause you would be going round in circles.
To do what you are looking for, you use a nested table, for instance with a CTE:
WITH numbering AS (
   SELECT (ROW_NUMBER() over
(order by ImportId, ScenarioId, SiteID, AssetID, LocalSKUID, WEEKID, MonthID)) RowID, *
FROM [JnJ_Version1].[dbo].[td_Production_Week]
SELECT *
FROM   numbering
WHERE RowID > 10000
Erland Sommarskog, SQL Server MVP, [email protected]

Is order in which the conditions given in the 'WHERE' clause are imortant

Hi All,
Is the order in which the conditions are given in the 'WHERE' clause are important for
performance with regard to oracle query plan.
Regards

Short answer: no.
Longer answer: Well. probably not. If you are using very old versions of the database or the rule-based optimizer, you can probably find some corner cases where it mattered. If you are using a vaguely recent version of the database with the cost based optimizer, it shouldn't matter-- the optimizer is free to evaluate the conditions in whatever order it would like and it chooses to do so in the order that it expects to be most efficient. That said, as the number of objects and conditions increases, the number of possible permutations the CBO tries to consider increase dramatically to the point that an exhaustive analysis of all possible conditions isn't feasible. In that case, the optimizer will have to make a reasonable effort to explore the set of possible plans rather than doing an exhaustive search-- the order of conditions is likely to matter slightly in the optimizer's choice of which branches to explore and which to prune if there are many conditions with similar (or identical) costs. Now, that being said, it is very unlikely that you could do anything useful with this knowledge that would be able to force the optimizer to do something that you'd want. It's possible to do, of course, it's just not a particularly useful way of influencing the optimizer.
Justin

WHERE clause order ox execution question

I dont understand order of execution of a WHERE clause, using a complex database
I want to write a SELECT statement with the following condition
... WHERE ( branch = 'main' ) AND ( type = 1 ) OR ( charge -1 AND charge = 2 )
My question is
<1> Can yoyu use parenthesis inside of a WHERE clause
<2> How would you write such a clause as above if you can not use parenthesis
Thanks

Just to echo what everyone else is saying, of course parentheses are syntactically valid and can make a difference to the logic. In you example though,
WHERE ( branch = 'main' ) AND ( type = 1 ) OR ( charge {noformat}<{noformat}> -1 AND charge <= 2 )is the same thing as
WHERE ( branch = 'main' AND type = 1 ) OR ( charge {noformat}<{noformat}> -1 AND charge <= 2 )and even
WHERE branch = 'main' AND type = 1 OR charge {noformat}<{noformat}> -1 AND charge <= 2because AND takes precedence over OR. You can think of it as a "stronger" operator.
However I would not use the last version because it's ambiguous to anyone reading it, and code like that can easily hide bugs. I would also not use the first version because all those redundant brackets are just confusing, making it almost as hard to read (and therefore prone to bugs) as the last version.
btw I've changed your example because I know this forum can swallow *{noformat}<{noformat}>* (I've used {noformat} tags to preserve it).
I'm not sure if any of this affects order of execution (and if it does, your Oracle version will make a difference).

Where clause and order by to DAO classes

Hi
Is it ok(I mean design wise) to pass the 'where clause' conditions and order by clause as a parameter to the method of DAO class?

Well, I would suggest you write seperate methods in your dao , one to select data without the where clause and one to select data with the where clause thrown in. If you have different 'where' clauses for selecting different kinds of data, have that many dao methods. The dao methods being specific know exactly what is the data that's coming in.
Lets assume you have a list of purchase orders and each purchase order is indetified by a unique id called PURCHASE_ORDER_ID.
1. The following code would populate a purchase order's details given an id.
private statis final String QUERY_1 = "select * from PURCHASE_ORDERS where PURCHASE_ORDER_ID = ? ";
PurchaseOrderModel getPurchaseOrderData(long poId){
     //get a prepared statement from your connection
     PreparedStatement pst = conn.prepareStatement(QUERY_1);
     //set the poId passed as params to your query
     pst.setLong(1, poId);
     ResultSet rs = pst.executeQuery();
     if(rs.next()){
          //populate data into a model
     finally{
          //clean up resources
     return model;
}2. The following code would return a list of PurchaseOrderModel's whose shipping date falls between a set of dates selected by the user.
private statis final String QUERY_2 = "select * from PURCHASE_ORDERS where SHIPPING_DATE between ? and ? ";
PurchaseOrderModel getPurchaseOrdersBetweenDates(list bindValues){
     //get a prepared statement from your connection
     PreparedStatement pst = conn.prepareStatement(QUERY_1);
     //set the dates passed as params to your query
     //we know that the List ought to contain only 2 dates
     pst.setDate(1, (Date)bindValues.get(0));
     pst.setDate(2, (Date)bindValues.get(1));
     ResultSet rs = pst.executeQuery();
     if(rs.next()){
          //iterate and populate data into a model
          //add model to a list
     finally{
          //clean up resources
     return list;
     3. This is more interesting - the dao method searches a list of Purchase Orders starting with a set of specific words. The words themselves may be one or many. This means that the number of '?' in your prepared statement may be dynamic. Each element of the list is a String that contains the start substring of a purcahse order name. For example - the list may contain elements like ["a", "ab", "c", "gh"] and the dao method returns all purchase order starting with these names.
private statis final String QUERY_3 = "select * from PURCHASE_ORDERS where ";
PurchaseOrderModel getPurchaseOrderNameMatches(list bindValues){
     //construct the query dynamically
     StringBuffer query = new StringBuffer(QUERY_3);
     int count = 0;
     for(Iterator itr = bindValues.iterator(); itr.hasNext();;){
          String value = (String)itr.next();
          query.append ("name like 'value%' ");
          if (count != 0 and (count+1 != bindValues.length)){
               query.append(" or ");
          count ++;
     //get a prepared statement from your connection
     PreparedStatement pst = conn.prepareStatement(query.toString());
     ResultSet rs = pst.executeQuery();
     if(rs.next()){
          //iterate and populate data into a model
          //add model to a list
     finally{
          //clean up resources
     return list;
To sum up,
1. You need as many methods as you have different kinds of searches (one method for each kind of 'where' clause).
2. The ejb/business layer would examine the data and decide on which method to call.
3. Increases coding effort, but makes the code clean and readable. Each layer does it's job. Thus we dont have ejbs forming 'where' clauses and so on.
Having said that, it really is your decision - you should take into consideration the following factors -
1. How big is the project ? If its a huge codebase developed by many people, then segregate the responsibilities clearly in each layer as I have outlined. For a small scale project, you could go with your approach.
2. Whats the take on maintenance and future add-ons ? Do you see the codebase growing with time ?
3. Is your project a commercial one - is it a product that needs to be maintained or is it a one-off development - develop once and you are done with it.
4. What are the design considerations ? Is somebody going to audit code for quality ? Or is it a academic one ?
You should take into account all these before deciding to go one way or the other.
A general thumb rule should be that you should be convinced that your code readable (maintainable), scalable and efficient. Anything that you do towards these ends is good code/design despite what people/books/patterns say, IMO.
cheers,
ram.

Order by in subquery ignores where clause

Following the suggestion to simulate "select first," I did the following:
select e.*,
(select * from (select dname from scott.dept d where d.deptno = e.deptno order by dname) t where rownum = 1) dname
from scott.EMP e;
The "order by dname" however, cause the subquery to ignore the where clause.
I know in this case, I can use a first_value() or min(), and it'll always return 1 row b/c of the PK. Still, any idea why it would ignore the where clause in the presence of an order by?
Thanks

My output:
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Mar 31 13:50:54 2006
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> select (select dname from (select dname from scott.dept d where d.deptno = e.deptno order by dname) t where rownum = 1) dname, e.* from scott.EMP e;
DNAME EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
ACCOUNTING 7369 SMITH CLERK 7902 17-DEC-80 800 20
ACCOUNTING 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
ACCOUNTING 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
ACCOUNTING 7566 JONES MANAGER 7839 02-APR-81 2975 20
ACCOUNTING 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
ACCOUNTING 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
ACCOUNTING 7782 CLARK MANAGER 7839 09-JUN-81 2450 10
ACCOUNTING 7788 SCOTT ANALYST 7566 19-APR-87 3000 20
ACCOUNTING 7839 KING PRESIDENT 17-NOV-81 5000 10
ACCOUNTING 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
ACCOUNTING 7876 ADAMS CLERK 7788 23-MAY-87 1100 20
ACCOUNTING 7900 JAMES CLERK 7698 03-DEC-81 950 30
ACCOUNTING 7902 FORD ANALYST 7566 03-DEC-81 3000 20
ACCOUNTING 7934 MILLER CLERK 7782 23-JAN-82 1300 10
14 rows selected.
SQL> select (select dname from (select dname from scott.dept d where d.deptno = e.deptno) t where rownum = 1) dname, e.* from scott.EMP e;
DNAME EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
RESEARCH 7369 SMITH CLERK 7902 17-DEC-80 800 20
SALES 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
SALES 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
RESEARCH 7566 JONES MANAGER 7839 02-APR-81 2975 20
SALES 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
SALES 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
ACCOUNTING 7782 CLARK MANAGER 7839 09-JUN-81 2450 10
RESEARCH 7788 SCOTT ANALYST 7566 19-APR-87 3000 20
ACCOUNTING 7839 KING PRESIDENT 17-NOV-81 5000 10
SALES 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
RESEARCH 7876 ADAMS CLERK 7788 23-MAY-87 1100 20
SALES 7900 JAMES CLERK 7698 03-DEC-81 950 30
RESEARCH 7902 FORD ANALYST 7566 03-DEC-81 3000 20
ACCOUNTING 7934 MILLER CLERK 7782 23-JAN-82 1300 10
14 rows selected.
SQL>

Select Statement -- Where Clause Execution Order

What is the order of execution of the "AND" and "OR" in the WHERE clause of a Select statement?
Are the "AND"'s executed from the top down, left to right? Is it the same for the "OR"'s execution?
Thanks for any help...

Not clear why you care. There is an order in which the optimizer parses the SQL (which may change from ver to ver), but this is a fairly quick operation. The order in which tables are visited and predicates evaluated is dependent on what the op[timizer does with the SQL.
Ken

Does the Order of the tablesjoins in Where clause matter in ORDERED hint?

The ORDERED hint requests that the tables listed in the FROM clause of a SQL statement be joined in the order specified. But does the order of the join in "where" clause matters?
Will be there any performance difference between below query? The order of the table in the FROM clause remains the same, but there is a difference in the order of conditions in the WHERE clause
SELECT /*+ ORDERED */ a.fp_i f
FROn iw_owner.revenue_fpct b,
dw_owner.fp_dinn c,
dw_owner.nanaged_at_dinn a,
dw_owner.at_dinn_curr d,
iw_owner.na_progran e,
dw_owner.fp_dinn_curr f,
dw_owner.fpn_of_at_dinn g
WHERE a.nacc_dinn_i = b.nacc_dinn_i
AND b.fp_dinn_i = c.fp_dinn_i
AND a.acc_i = d.acc_i
AND a.acc_nacc_c = e.npn_pro_c
AND a.fp_i = f.fp_i
AND b.org_fpn_dinn_i = g.org_fpn_dinn_i(+)
AND c.fp_i IN ('JG 04')
AND b.dte_dinn_i BETWEEN '1-Apr-2011' and '30-Apr-2011'
SELECT /*+ ORDERED */ a.fp_i f
FROn iw_owner.revenue_fpct b,
dw_owner.fp_dinn c,
dw_owner.nanaged_at_dinn a,
dw_owner.at_dinn_curr d,
iw_owner.na_progran e,
dw_owner.fp_dinn_curr f,
dw_owner.fpn_of_at_dinn g
WHERE c.fp_i IN ('JG 04')
AND b.dte_dinn_i BETWEEN '1-Apr-2011' and '30-Apr-2011'
AND b.fp_dinn_i = c.fp_dinn_i
AND a.nacc_dinn_i = b.nacc_dinn_i
AND a.acc_i = d.acc_i
AND a.acc_nacc_c = e.npn_pro_c
AND a.fp_i = f.fp_i
AND b.org_fpn_dinn_i = g.org_fpn_dinn_i(+)
Thanks

Gangadhar Reddy wrote:
Does it matter the order of first 2 tables?This question makes me really wonder. It's fairly easy to see how explain changes when using hints.
Your question indicates that you do not look at explain plans?
Then why are you asking about hints in the first place?
Using hints is something you do when you want to force a specific execution plan as part of some investigation, because you know something that the optimizer does no, or you have found a bug in the optimizert.
In all cases you know exactly what you are doing.
The /*+ ORDERED */ is all about you telling the optimizer to join the tables in the order you specified them in the from clause.
As to your original question, there exists a similar ORDERED_PREDICATES hint.
Regards
Peter

Is it possible to use LONG columns in WHERE clause or ORDER BY?

Is it possible to use LONG columns in WHERE clause or ORDER BY?

Hi,
LONG data type is deprecated, maybe could you change your column type to LOB ?
Nonetheless below is a workaround which may fit your needs if forced to use LONG.
It uses a function which returns you a CLOB. It allows you to use the converted "LONG" column in a WHERE clause.
Then if you want to order by you have to convert the CLOB to a VARCHAR using DBMS_LOB.SUBSTR.
SQL> CREATE TABLE my_table (id NUMBER, description LONG);
Table created.
SQL> INSERT INTO my_table VALUES (1, 'FIRST LONG');
1 row created.
SQL> INSERT INTO my_table VALUES (2, 'ANOTHER LONG');
1 row created.
SQL> COMMIT;
Commit complete.
SQL> CREATE TYPE my_type_row AS OBJECT (id INTEGER, description CLOB);
2 /
Type created.
SQL> CREATE TYPE my_type_table AS TABLE OF my_type_row;
2 /
Type created.
SQL> CREATE OR REPLACE FUNCTION get_my_long
2     RETURN my_type_table
3     PIPELINED
4 AS
5     v_tab   my_type_table := my_type_table ();
6 BEGIN
7    FOR cur IN (SELECT id, description FROM my_table)
8 LOOP
9        PIPE ROW (my_type_row (cur.id, cur.description));
10 END LOOP;
11 RETURN;
12 END;
13 /
Function created.
SQL> SELECT
2     id,
3     description
4 FROM
5     TABLE (get_my_long ())
6 WHERE
7     description LIKE '%LONG'
8 ORDER BY
9     DBMS_LOB.SUBSTR(description);
ID DESCRIPTION
   2 ANOTHER LONG
   1 FIRST LONG
SQL> SELECT
2     id,
3     description
4 FROM
5     TABLE (get_my_long ())
6 WHERE
7     description LIKE 'FI%';
ID DESCRIPTION
   1 FIRST LONG
SQL>Kind regards,
Ludovic

Dynamic Order by with user defined Where clause...

Hello!
I have a block based on a table, with no order by set and no where clause.
The block is queryable so users can filter the data to be retrieved.
Each of the columns on the form have a button above which requeries the block, applying the order by (SET_BLOCK_PROPERTY ( 'B12', ORDER_BY, :bc1.h_b12_custom_orderby ); )
The problem is that each time the block is requeried the user definied filter criteria is lost. Is there any way I can get a handle on this and maintain the filtering?
GET_BLOCK_PROPERTY(item, DEFAULT_WHERE); only retrieves the query entered while in design mode so this won't work.
I'm using Oracle Forms 6i, web based. Any suggestions are very much appreciated.
Thanks in advance,
Jay

Many thanks for your response Hedy,
Below is the procedure I used to achieve this.
I found GET_BLOCK_PROPERTY ( p_block, LAST_QUERY ) worked better than :SYSTEM.last_query. As the first time it is called within a block :SYSTEM.last_query returned the query made in another block - which I'm sure has it's applications.
Thanks again,
Jay
PROCEDURE set_last_query_where ( p_block IN VARCHAR2
, p_where IN VARCHAR2 DEFAULT NULL )IS
l_last_query VARCHAR2(10000);
l_last_where VARCHAR2(10000);
BEGIN
IF p_where IS NULL THEN
l_last_query := UPPER(GET_BLOCK_PROPERTY ( p_block, LAST_QUERY ));
l_last_where := SUBSTR ( UPPER ( l_last_query),
INSTR ( l_last_query, 'WHERE')+6, INSTR(SUBSTR(UPPER(l_last_query), INSTR(l_last_query, 'WHERE')+8), 'ORDER BY'));
ELSE
l_last_where := p_where;
END IF;
SET_BLOCK_PROPERTY ( p_block, DEFAULT_WHERE, l_last_where );
EXCEPTION
     WHEN FORM_TRIGGER_FAILURE THEN
     ref_raise_ftf;
     WHEN OTHERS THEN
     ref_others( 'P-SLQW' );
END;

Order of Where clause

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