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1. Top results related to composite index in oracle

   • Composite index required does not exist, yet defined in index.yaml

     Top Answer

     Answered Sep 19, 2018 · 2 votes

     Though in the comment I simply suggest select * (that's the best way, I do think)

     There is a way make your query work.

     - kind: ParticleEvent properties: - name: device_id - name: published_at direction: desc - name: current_temperature - name: target_temperature

     The reason why is select is done at the end and thus you need the index of current_temperature and target_temperature in a lower level.

     Why I don't suggest this way is because, when your data grows and you need more combination of indexing just because of select specific columns. Your index size will grow exponentially.

     But let's say if you sure you will just use this once and always query the data like this, then feel free to indexing it.

     Or, if the connection bandwidth between your computer and google cloud is very small such that downloading more data causes you lag.

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     1/5

   • Composite Clustered Index in SQL Server

     Top Answer

     Answered Jul 08, 2010 · 22 votes

     Yes, you can only have a single clustered index per table - the data is physically arranged by that index, so you cannot have more than one.

     I would however not advise to use a composite clustered index. Why? Because the clustered index should always be:

     • as small as possible - INT with 4 byte is perfect
     • stable - never change, so you don't have rippling updates through all your indices
     • unique - otherwise, SQL Server will have to "uniquify" your entries with artifical 4-byte values
     • optimal would be: ever increasing

     INT IDENTITY is perfect as a clustered index - I would advise you keep it that way.

     The clustered index column (or set of columns) is also added to each and every entry of each and every nonclustered index on that same table - so if you make your clustered index large, 20, 50 bytes or more, you begin to be wasting a lot of space - on disk and in your server's memory, which generally degrades your system performance.

     Read all about clustered indices and what they should be to be good clustered indices here:

     • GUIDs as PRIMARY KEYs and/or the clustering key
     • The Clustered Index Debate Continues...
     • Ever-increasing clustering key - the Clustered Index Debate..........again!

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     2/5

   • Composite Foreign Key - Possible In Oracle?

     Top Answer

     Answered Dec 08, 2011 · 5 votes

     Try this:

     CREATE TABLE employee_licence_certificate( emp_id NUMBER(4) REFERENCES employee(emp_id) , licence_cert_code VARCHAR2(6) REFERENCES licence_certificate(licence_cert_code) , date_earned DATE NOT NULL ,PRIMARY KEY (emp_id, licence_cert_code))

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     3/5

   • index in oracle for wild card

     Top Answer

     Answered Apr 18, 2023 · 1 votes

     If the wild card is in the middle or the end and the leading characters before the wildcard match a relatively small number of records, then you should use the LIKE operator. Replace the "x" with _ :

     WHERE column LIKE 'AAA___CCC'-

     If your user can't use _ and insists on an 'x' wildcard, replace it with a _ in your SQL:

     WHERE column LIKE REPLACE('AAAxxxCCC','x','_')-

     This is my primary answer. It won't be fast, however, if you have a ton of rows starting with AAA. If you run into this problem, then there are some possibilities depending on what patterns are common. If you always look at the first three characters and the last three, you can SUBSTR them out and index that function:

     CREATE INDEX i_first3 on mytable(SUBSTR(mycolumn,1,3));CREATE INDEX i_last3 on mytable(SUBSTR(mycolumn,-3,3));-SELECT * FROM mytable WHERE SUBSTR(mycolumn,1,3) = 'AAA' AND SUBSTR(mycolumn,-3,3) = 'CCC'

     Obviously this won't work if the user can wild card any position and you can't predict which one. But you can do some edgy things like creating a separate functioned based index for each number of final characters and then based on the value the user supplies, find the number of characters after the last wildcard and use a substring on that, plus a LIKE on the rest:

     CREATE INDEX i_last1 on mytable(SUBSTR(mycolumn,-1),mycolumn);CREATE INDEX i_last2 on mytable(SUBSTR(mycolumn,-2),mycolumn);CREATE INDEX i_last3 on mytable(SUBSTR(mycolumn,-3),mycolumn);CREATE INDEX i_last4 on mytable(SUBSTR(mycolumn,-4),mycolumn);CREATE INDEX i_last5 on mytable(SUBSTR(mycolumn,-5),mycolumn);CREATE INDEX i_last6 on mytable(SUBSTR(mycolumn,-6),mycolumn);CREATE INDEX i_last7 on mytable(SUBSTR(mycolumn,-7),mycolumn);...etc..SELECT * FROM mytable WHERE mycolumn LIKE REPLACE('AxABBBCCC','x','_') AND SUBSTR(mycolumn,-7) = SUBSTR('AxABBBCCC',-7)

     That will use i_last7 doing a seek (binary search) on the last 7 digits, then scan through the leaf nodes applying the LIKE operator on the whole mycolumn column which is the second column in the index. It could perform a lot better than LIKE with only one character before a wildcard.

     You can also reverse the value with REVERSE and index that, then decide whether to use LIKE on the normal value (if the wildcard is further into the value), or on the reverse of the value (if the wildcard is near the front).

     CREATE INDEX i_reverse on mytable(REVERSE(mycolumn));-SELECT * FROM mytable WHERE REVERSE(mycolumn) LIKE REVERSE(REPLACE('xxABBBCCC','x','_'))

     vs.

     SELECT * FROM mytable WHERE mycolumn LIKE REPLACE('AAABBBCxx','x','_')

     Anyway, you get the point - your options depend on your query patterns and your data. Hopefully the simple LIKE without any function-based index will satisfy your needs and you won't need all this extra stuff. You won't know until you try it and see how it performs.

     Lastly and hopefully not too often, you can add a parallel attribute to the table so that if Oracle sees a wildcard at the beginning of the string and goes for a full table scan, at least it will read it in parallel with direct path reads.

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     4/5

   • oracle composite primary key vs index

     Top Answer

     Answered Apr 14, 2015 · 1 votes

     As @Sylvain_Leroux points out, the term "better" is actually very ambiguous depending on your goals because there are tradeoffs to both approaches.

     Ensure Composite Key is Actually Unique

     First of all, if you want to use a composite primary key out of the foreign keys, then you must be sure that the combination of the foreign keys will be truly unique for each record. Otherwise, of course, you won't be able to use them as a primary key. If instead you are describing using a composite key made up of the foreign keys plus a surrogate key, that's kind of the worst of both worlds and is generally frowned upon.

     ETL Back Room Considerations

     The choice you are considering is a common one in OLAP, where a designer must choose whether or not to use a surrogate key for the fact table or a composite key comprised of the keys of the dimension tables. This advice from page 487 of Ralph Kimball's The Data Warehouse Toolkit Third Edition would therefore apply to your situation (you can consider your table as being analogous to what he describes as a fact table, and the foreign keys are for tables that he refers to as dimensions):

     Fact table surrogate keys have a number of uses in the ETL back room. First, as previously described, they can be used as the basis for backing out or resuming an interrupted load. Second, they provide immediate and unambiguous identification of a single fact row without needing to constrain multiple dimensions to fetch a unique row. Third, updates to fact table rows can be replaced by inserts plus deletes because the fact table surrogate key is now the actual key for the fact table. Thus, a row containing updated columns can now be inserted into the fact table without overwriting the row it is to replace. When all such insertions are complete, then the underlying old rows can be deleted in a single step. Fourth, the fact table surrogate key is an ideal parent key to be used in a parent/child design. The fact table surrogate key appears as a foreign key in the child, along with the parent's dimension foreign key.

     Performance Considerations

     From a performance perspective, the records are stored in order by primary key(s) physically on the disk. That makes reads based on queries that use a foreign key (or keys) for lookup faster, but also could mean that writes will be slower if they require inserting records at points other than at the end. This is because the DBMS will have to physically move the records to make room (this is slightly oversimplified because there are some schemes employed by the DBMS to combat this, but they are overwhelmed if the inserts are numerous enough).

     If you were to use a surrogate key, the insert problem wouldn't be an issue, but of course in situations where you are looking up by foreign keys, you wouldn't get the advantage of having your data in order physically on the disk. Assuming you would put an index on each foreign key, then that would add some overhead to insert tasks because the DBMS has to update multiple indices.

     All of this is only noticeable with large amounts of data and will not make much of a difference for a relatively small amount of data.

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     5/5

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2. docs.oracle.com › en › databaseIndexes and Index-Organized Tables - Oracle Help Center

   docs.oracle.com › en › database

   • Cached

   A composite index, also called a concatenated index, is an index on multiple columns in a table. Place columns in a composite index in the order that makes the most sense for the queries that will retrieve data.

3. stackoverflow.com › questions › 795031sql - How do composite indexes work? - Stack Overflow

   stackoverflow.com › questions › 795031

   • Cached

   Composite indexes work just like regular indexes, except they have multi-values keys. If you define an index on the fields (a,b,c) , the records are sorted first on a, then b, then c. Example:

4. www.plsql.co › composite-indexCreate Composite Index - Oracle PL/SQL Tutorial

   www.plsql.co › composite-index

   • Cached

   Create Composite Index example. . -- create Composite Index . CREATE UNIQUE INDEX orders_unique_index . ON ORDERS (ORDER_ID, COURSE_ID, STUDENT_ID) ; Output: unique index ORDERS_UNIQUE_INDEX created. Check indexes. select INDEX_NAME, INDEX_TYPE, UNIQUENESS. from USER_INDEXES. WHERE table_name='ORDERS'; . Output: Create Function-Based Index.

5. stackoverflow.com › questions › 55255998performance - Oracle Composite Index Performace - Stack Overflow

   stackoverflow.com › questions › 55255998

   • Cached

   Mar 20, 2019 · If I make COLUMN_01, COLUMN_02 and COLUMN_03 (all columns in WHERE clause) as composite index without changing existing indexes, will it improve performance? If so, is there an order for composite index columns?

6. docs.oracle.com › en › databaseCREATE INDEX - Oracle Help Center

   docs.oracle.com › en › database

   • Cached

   Use the CREATE INDEX statement to create an index on: One or more columns of a table, a partitioned table, an index-organized table, or a cluster. One or more scalar typed object attributes of a table or a cluster. A nested table storage table for indexing a nested table column.

7. docs.oracle.com › en › databaseUsing Indexes in Database Applications - Oracle Help Center

   docs.oracle.com › en › database

   • Cached

   The index is a composite index on three columns: a virtual column that represents the expression a+b*(c-1), column a, and column b. The query uses the indexed expression in its WHERE clause; therefore, it can use an index range scan instead of a full index scan.

8. stackoverflow.com › questions › 933783sql - When to use composite indexes? - Stack Overflow

   stackoverflow.com › questions › 933783

   • Cached

   Jun 1, 2009 · Composite indexes are useful when your SELECT queries use those columns frequently as criteria in your WHERE clauses. It improves retrieval speed. You should avoid them if they are not necessary. This article provides some really good information.

9. asktom.oracle.com › pls › asktomComposite index - Ask TOM - Oracle Ask TOM

   asktom.oracle.com › pls › asktom

   • Cached

   Aug 30, 2001 · My intention was to create separate indexes on each column, but I've been told that Oracle will normally only ever choose one index per table for access so it's better to create a composite index on (surname, first_name) instead.

10. dba.stackexchange.com › questions › 243517oracle - Is it better a composite index (item, item_type) or...

    dba.stackexchange.com › questions › 243517

    • Cached

    Jul 23, 2019 · create table a_table. ( item varchar2(30) not null, item_type varchar2(10) not null, -- other columns. ); create unique index idx_1 on a_table (item_type, item); -- reading item_X. select ... from a_table where item='...' and item_type='item_X';

11. dba.stackexchange.com › questions › 160649oracle - Composite indexes: Most selective column first? -...

    dba.stackexchange.com › questions › 160649

    • Cached

    Jan 11, 2017 · Most selective first is useful only when this column is in the actual WHERE clause. When the SELECT is by a larger group (less selective), and then possibly by other, non-indexed values, an index with less selective columns may still be useful (if there's a reason not to create another one).