How Select query works in Oracle

When we give SELECT * FROM EMP; How does oracle respond?
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don

  • Oct 18th, 2005
 

when u give  SELECT * FROM EMP;

the server check all the data in the EMP file and it displays the data of the EMP file

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don

  • Oct 18th, 2005
 

when u give  SELECT * FROM EMP;

the server check all the data in the EMP file and it displays the data of the EMP file

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Shanker

  • Oct 24th, 2005
 

Its gives complete employees details which are present in emp table.

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Muruganandam

  • Oct 24th, 2005
 

If we give select * from emp then oracle response by displaying all the records with all its column. This is used to view the full sturcture of the table with all its records with field name as its column title.

Rajesh Sakhamuri

  • Nov 3rd, 2005
 

Which data u have in the EMP table at the database,that data willbe displays.

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asdf

  • Nov 3rd, 2005
 

the SQL parser will first checks the which command it is.And then the table table, columns which are selected and then the display of selected lsit.

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Dhayanand darshanala

  • Nov 3rd, 2005
 

Select All the rows from the Emp table

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shobhit sharma

  • Nov 8th, 2005
 

when we give select * from emp; The server search for the database schema called " Emp" here. If there exists any schema called "emp", then it checks its all attributes then match this attribute with the arguments in after the select statement. If everthing is allright then it will display all the rows with all its attributes.

bhaskar

  • Nov 9th, 2005
 

wellfirst it checks the data dictionary part in the blockand then it checks the table emp and the concerned record block leveland gives the answer

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shuaib

  • Nov 11th, 2005
 

it will return the all rows from emp table.

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ravi.chand

  • Nov 15th, 2005
 

oracle will search for the emp table in the database and select the rows randomly.

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veeraswamy

  • Dec 9th, 2005
 

first it check the emp table present or not,

if it is present it wiil display all the contents of emp table.

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Deepa Jayaraj

  • Dec 16th, 2005
 

Select * from emp;

At first the query will be checking for any syntax error. Since * has been given as the column to be selected, it will refer Data dictionary for all its columns and form the query to be compiled. Then SQL Parser will parse the query. Optimizer will choose either cost based Optimizer or rule based optimizer for performing this query. Then SQL Execution engine executes and gives the result ie., it will display all the records of Emp table.

Ritesh P. Medhe

  • Dec 22nd, 2005
 

When select * or any query is fired against the database. The database engine first checks whether the user has rights to perform the specified action or not.

If he do not have rights to do so an error message wll be shown.

If he is allowed to do that the database engine will check for the specified object in the datafiles and display the results accordingly.

Thanks

Ritesh

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srinivasakumar

  • Mar 27th, 2006
 

first it checks for the schema whether that emp table is present in schema like (scott).then it selects all the columns and display them

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ajay kumar verma

  • Apr 6th, 2006
 

the server check all the data in the EMP file and it displays the data of the EMP file

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nirav

  • Jun 17th, 2006
 

in this statement select *from emp

step 1 : server check for the syntex is right or not

step 2: than it check for the object if it is exits it retrive the information from the object and give it bck to user.if not it display the error message : object does not exits.

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sim

  • Jan 10th, 2007
 

yes it displays all the rows and columns related to emp table

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macmanoj

  • Sep 19th, 2012
 

when you insert SELECT as the DRS statement,it starts working in the column level and retrieving the data from the column of the perticular table.The SELECT statement is a predefined statement in sql engine which performs in the column level only. Let us consider the EMP table, when we insert,

SQL>SELECT Ename from emp;

it will display all the employee name from the emp table.


suppose,
i insert

SQL>SELECT * from emp;

the above querry will display all the information from emp or we can say the entire information along with the structure of the emp table.SELECT works like a pointer which points the particular memory area of the particular column queried in your statement.where as "SELECT *" works as virtual pointer on the table level and derives the entire structure and information from the table.

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Sathya

  • Sep 23rd, 2012
 

It will fetch all the data from employee table..then u give a select * command..

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sainath

  • Sep 24th, 2012
 

syntax verification done from client only not in the server only valid sequel statements are send to the server if syntax is not correct client throws error

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Rakesh

  • Jun 29th, 2014
 

Check for syntax correct Then it will check weather the table is present or not in database is nothing but a Parsing
fetch the data

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Sandip Muke

  • Jul 29th, 2016
 

First it will do the syntax/ semantic check and if it is correct then an only that statement forward to the Oracle RDBMS server. After that Oracle will check whether that user has privilege or not. Then it enters into the Shared pool area in DD cache/ Row cache and check what type of this statement is SQL, PLSQL or Trigger and also check whether that statement is fired by anyone previously, if same statement already fired then it found the matching value and does the Soft parse and if not found then, it will generate the some hash value and store that hash value in namespace along with that statement and perform the Hard parse which is more costlier.

In that case Oracle does not know anything about table name, about *, nothing, so in that case it will ask to Data Dictionary what is meant by EMP (table) so DD tells to Oracle that EMP is a table.

Next Oracle will ask what is meant by *, who fired that select statement, whether he has access on that table and if yes then how I will go to perform the output of that table, are the statistics are available there?, etc. So depend upon the stats optimizer generate the some plan. This is end of Parsing phase.

Next is Execute phase: Whatever plan have selected it get into action.

Next is Fetch: After execution it fetch the data one row at a time and we get the required output.

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Abdul Rahman

  • Jul 18th, 2017
 

All rows from the EMP table are returned (output).

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