Problem Statement:You want to assign a number/rank representing their positions in the result.Solution:Oracle provides the RANK analytic function to generate a ranking number for rows in a result set. To demonstrate we will rank students by fees, from highest paid down. The following SELECT statement uses the rank function to assign these values.ExampleSELECT student_id,        first_name,        last_name,        fees,        RANK() OVER (ORDER BY fees DESC) AS rnk FROM students;Outputstudent_idfirst_namelast_namefeesrnk100SMITHJAMES240001101JOHNSONJOHN170002102WILLIAMSROBERT170002108RODRIGUEZJOSEPH120084103BROWNMICHAEL90005109WILSONTHOMAS90005110MARTINEZCHRISTOPHER82007112TAYLORPAUL78008111ANDERSONDANIEL77009113THOMASMARK690010104JONESWILLIAM600011105MILLERDAVID480012106DAVISRICHARD480012107GARCIACHARLES420014RANK behaves similar to any other analytic function, operating in a second pass over the result set once non analytic processing is ... Read More

Problem Statement:You want to improve the performance of frequently used queries.Solution:We have to use Oracle’s result cache to store the query results of frequently used SQL, so they can be retrieved quickly for future use when the same query has been executed.The result cache is new additon to Oracle 11g, which will allow us store results from often-used queries in memory for quick and easy retrieval.ExampleSELECT /*+ result_cache */      e.class_id,      min_fees,      max_fees FROM students e ,jobs j WHERE e.class_id = j.class_id GROUP BY e.class_id, min_fees, max_fees;To demonstrate how it is used, we will check ... Read More

Problem Statement:You are performing a INSERT statement, and it is performing slower than needed. You want to optimize the INSERT statement.Solution:By using the APPEND or APPEND_VALUES hint with INSERT statement, we can significantly speed up the process of performing an insert operation on the database. Here is an example of the performance savings using the APPEND hint.SQL without OptimizationINSERT INTO students SELECT * FROM students_bkp;Output-- Output 22141998 rows created. Elapsed: 00:03:11.21 ------------------------------------------------- | Id  | Operation                | Name         | ------------------------------------------------- |   0 | INSERT STATEMENT     ... Read More

Problem Statement:You want to enforce XML schema validity on XML data stored in your database.Solution:Oracle provides the DBMS_XMLSCHEMA.REGISTERSCHEMA function to define XML schemas within the Oracle database. Inorder to validate the xml data generated, we need to register the schema. While registering the schema, the format must match the xml format generated or register the schema based on how you want to generate the xml .The registration provides two key features. First, it allows Oracle to identify the external location or locations from which it can source the schema. Second and most important, REGISTERSCHEMA parses the schema for syntactical correctness ... Read More

Problem Statement:You want to generate a complex XML document with nesting values at different levels.Solution: Oracle has quite a number of functions and procedures for generating XML from regular data. To demonstrate the usage, I will be using the studentdata. We will assume we would like to use the student_id of an student as an XML attribute to the root elementand add detail on fees, specifying the payment period as an attribute, and adding currency details.Oracle functions XMLROOT, XMLELEMENT, and XMLATTRIBUTE provide full control over the structure of your desired XML.XMLROOT provides the necessary XML header to turn our results ... Read More

Problem Statement:You need to extract a portion/subset of elements values from an XML document.Solution:We can leverage Oracle’s EXTRACT function which supports XMLTYPE datatype. EXTARCT function provides the ability to preserve XML element name and attribute constructs by returning the results as an XMLTYPE value.Assume, we have below XML in a table tmp_xml_gen from which we wanted to extract the customer names.Example       134     taylor.cauchon@internalmail     Taylor Cauchon                   921         COMPLETE               ... Read More

Problem Statement:You need to extract individual elements values from an XML document.Solution:Oracle provides the XMLTABLE function to manipulate XML documents using XQuery and column mapping to Oracle datatypes. Using XMLTABLE, we can identify and use data elements in an XML document in a relational way.Let us assume, below XML document is stored in a table tmp_xml_gen from which we wanted to extract the elements. We have customer details along with order related information.Example       134     taylor.cauchon@internalmail     Taylor Cauchon                   921     ... Read More

Problem Statement:You need to store native XML data into a relational table in your database.Solution:Oracle have several ways of storing XML documents. One way of storing data where our XML doesn’t need to be altered, or where a portion of the XML can be extracted with XSLT, is to use XMLTYPE data casting.We will use the XMLTYPE call to cast the text provided into the XMLTYPE datatype. In the background Oracle XMLTYPE supports CLOB datatype, because XML is stored internally as a CLOB. This means we can use the same approach to casting, passing the call to XMLTYPE a string ... Read More

Problem Statement:You need to convert data stored in traditional form in your database to XML document.Solution: Oracle have many different functions for converting data to XML format. Some of the functions Oracle provides for converting relational data to XML are the SYS_XMLGEN, DBMS_XMLGEN, and XMLELEMENT functions.We will be using SYS_XMLGEN to convert rows to XML.The SYS_XMLGEN function returns a block of XML based on a row/s or row like expression. SYS_XMLGEN can take a literal value, a single column, or a user defined type as input parameter.We will be creating XML from students data for an student record.We will begin ... Read More

Problem Statement:You want to write a common procedure to find and remove duplicates from any table and columns in Oracle.Solution:We can use Oracle’s internal ROWID value for uniquely identifying rows in a table along with the OLAP function row_number with partition clause. The sample syntax to acheive this would like below.delete from table where rowid in   (... query here ...)To demonstrate the usage, we will begin by creating sample data.Example-- table with tennis player rankings DROP TABLE atp_stats; CREATE TABLE atp_stats ( player_rank NUMBER NOT NULL,   player_name VARCHAR2(100) NOT NULL,   time_range  TIMESTAMP(6)); -- sample records ... Read More