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merge vs update statement

ushitakiMar 30 2007 — edited Mar 30 2007
I try to tune SQL in another [url http://forums.oracle.com/forums/message.jspa?messageID=1762095#1762095]thread. 
And then I find out one of difference between 'merge' and 'update' 
that is number of execution. 
 
Update : Rows * Rows
Merge  : Rows
 
Can we tune my update statement up to near merge? 

Here is tkprof results. 
There are only 300 rows in mytable for test.
 
 /**** UPDATE ****/
 
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 27  (USHI)   (recursive depth: 1)
 
Rows     Row Source Operation
-------  ---------------------------------------------------
      1  SORT AGGREGATE (cr=3 pr=0 pw=0 time=125 us)
    300   TABLE ACCESS FULL MYTABLE (cr=3 pr=0 pw=0 time=338 us)
 

Rows     Execution Plan
-------  ---------------------------------------------------
      0  SELECT STATEMENT   MODE: HINT: ALL_ROWS
      1   SORT (AGGREGATE)
    300    TABLE ACCESS (FULL) OF 'MYTABLE' (TABLE)

********************************************************************************

update mytable t1
 set flag =
 (select 1+rn-last_value(rn2 ignore nulls) over (order by id) new_flag
    from
      (select
        rowid row_id
       ,id
       ,row_number() over (order by id) rn
       ,case when col1 = lag(col1) over (order by id)
              and col2 = lag(col2) over (order by id)
              and col3 = lag(col3) over (order by id)
             then null
             else row_number() over (order by id)
        end rn2
      from mytable
      ) t2
   where t2.row_id = t1.rowid
   )
 
call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          2          0           0
Execute      1      0.50       0.50          0        903        606         300
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.50       0.50          0        905        606         300
 
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 27  (USHI)
 
Rows     Row Source Operation
-------  ---------------------------------------------------
      0  UPDATE  MYTABLE (cr=903 pr=0 pw=0 time=502019 us)
    300   TABLE ACCESS FULL MYTABLE (cr=3 pr=0 pw=0 time=635 us)
    300   WINDOW BUFFER (cr=900 pr=0 pw=0 time=494110 us)
    300    VIEW  (cr=900 pr=0 pw=0 time=488138 us)
  90000     WINDOW SORT (cr=900 pr=0 pw=0 time=431450 us)
  90000      TABLE ACCESS FULL MYTABLE (cr=900 pr=0 pw=0 time=94585 us)
 

Rows     Execution Plan
-------  ---------------------------------------------------
      0  UPDATE STATEMENT   MODE: ALL_ROWS
      0   UPDATE OF 'MYTABLE'
    300    TABLE ACCESS (FULL) OF 'MYTABLE' (TABLE)
    300    WINDOW (BUFFER)
    300     VIEW
  90000      WINDOW (SORT)
  90000       TABLE ACCESS (FULL) OF 'MYTABLE' (TABLE)

********************************************************************************
 
 
 /**** MERGE ****/
  
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 27  (USHI)   (recursive depth: 1)
 
Rows     Row Source Operation
-------  ---------------------------------------------------
      1  SORT AGGREGATE (cr=3 pr=0 pw=0 time=113 us)
    300   TABLE ACCESS FULL MYTABLE (cr=3 pr=0 pw=0 time=328 us)
 

Rows     Execution Plan
-------  ---------------------------------------------------
      0  SELECT STATEMENT   MODE: HINT: ALL_ROWS
      1   SORT (AGGREGATE)
    300    TABLE ACCESS (FULL) OF 'MYTABLE' (TABLE)
 
********************************************************************************

merge into mytable t1
using
 (select row_id, 1+rn-last_value(rn2 ignore nulls) over (order by id) new_flag
    from
      (select
        rowid row_id
       ,id
       ,row_number() over (order by id) rn
       ,case when col1 = lag(col1) over (order by id)
              and col2 = lag(col2) over (order by id)
              and col3 = lag(col3) over (order by id)
             then null
             else row_number() over (order by id)
        end rn2
      from mytable
      )
   ) t2
   on (t2.row_id = t1.rowid)
 when matched then
      update set flag = new_flag
 when not matched then
      insert values (null,null,null,null,null)
 
call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.03       0.02          0          4          0           0
Execute      1      0.00       0.00          0          6        308         300
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.03       0.03          0         10        308         300
 
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 27  (USHI)
 
Rows     Row Source Operation
-------  ---------------------------------------------------
      2  MERGE  MYTABLE (cr=6 pr=0 pw=0 time=9505 us)
    300   VIEW  (cr=6 pr=0 pw=0 time=6530 us)
    300    HASH JOIN OUTER (cr=6 pr=0 pw=0 time=5930 us)
    300     VIEW  (cr=3 pr=0 pw=0 time=4164 us)
    300      WINDOW BUFFER (cr=3 pr=0 pw=0 time=3557 us)
    300       VIEW  (cr=3 pr=0 pw=0 time=3284 us)
    300        WINDOW SORT (cr=3 pr=0 pw=0 time=2080 us)
    300         TABLE ACCESS FULL MYTABLE (cr=3 pr=0 pw=0 time=346 us)
    300     TABLE ACCESS FULL MYTABLE (cr=3 pr=0 pw=0 time=352 us)

********************************************************************************

Comments

mNem
Answer

Your table name contains invalid character.

Check for the permitted characters in the table name.

https://dev.mysql.com/doc/refman/5.7/en/identifiers.html

Invoke the below two statements on http://rextester.com/l/mysql_online_compiler  and check the results.

Create table if not exists 2015-SE-001 (id INTEGER not null primary key auto_increment, name varchar(30),  totalTheoryClasses INTEGER, totalLabs INTEGER, WeekNo INTEGER, DaysPresent INTEGER, DaysAbset INTEGER, Percentage FLOAT);

Create table if not exists 2015_SE_001 (id INTEGER not null primary key auto_increment, name varchar(30),  totalTheoryClasses INTEGER, totalLabs INTEGER, WeekNo INTEGER, DaysPresent INTEGER, DaysAbset INTEGER, Percentage FLOAT);

On the other hand, why would you need to create the tables on the fly?

Marked as Answer by Zulfi Khan · Sep 27 2020
unknown-7404

This means that I want to parameterize the table name.

That means you are doing SEVERAL things wrong.

1. You don't 'parameterize' table names in queries. The table name can NOT be a bind variable

2. You should NOT be using a parameter for the table name anyway. You should NOT be creating multiple identical tables with different names. That usually means you have the wrong data model.

This appears to be a continuation of your previous issue

How to check empty Excel cell using while loop?

Until you tell people ALL of the requirements about the real problem you are trying to solve it is hard to give you help.

Zulfi Khan

Hi,

Thanks for your suggestions. I have solved this prob:

2. You should NOT be using a parameter for the table name anyway. You should NOT be creating multiple identical tables with different names. That usually means you have the wrong data model.

Its easy. I am keeping each students' record in a separate table. And the Head can check it with a simple 'Select' query but now there is table name alteration he has to remember. I mean its simple to say "Select * from 2015_SE_21" as compared to using a where clause.

<On the other hand, why would you need to create the tables on the fly?>

I have to read excel sheet for roll numbers & then create tables for each rollNo & each table will contain attendance data for each specific student.

My code is:

import java.io.*;

import jxl.Sheet;

import jxl.Workbook;

import jxl.read.biff.BiffException;

import javax.swing.*;

import java.sql.*;

/**

*

* @author HP

*/

public class ReadExcelSheetMain6 {

private static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; 

private static final String DB_URL = "jdbc:mysql://localhost/attendance";

   //  Database credentials

private static final String USER = "root";

private static final String PASS = "z";

private Connection conn = null;

private Statement stmt = null;

PreparedStatement pStmt = null;

    /**

     * @param args the command line arguments

     */

    public void readExcel() throws BiffException, IOException {

String FilePath = "D:\\Marks-2A-SE-OOP-2015.xls";

FileInputStream fs = new FileInputStream(FilePath);

Workbook wb = Workbook.getWorkbook(fs);

// TO get the access to the sheet

Sheet sh = wb.getSheet("Sheet1");

               

// To get the number of rows present in sheet

int totalNoOfRows = sh.getRows();

                JOptionPane.showMessageDialog(null, "KKK totalNoOfRows = " + totalNoOfRows);

// To get the number of columns present in sheet

int totalNoOfCols = sh.getColumns();

                JOptionPane.showMessageDialog(null, "GGG totalNoOfCols = " + totalNoOfCols);

                int row=8;

                int col=1;

                String rollNo=null;

                String newRollNo = null;

               

               

                //for ( row = 8; row < totalNoOfRows; row++) {

                   rollNo = sh.getCell(col, row).getContents();

                   newRollNo = rollNo.replace('-','_');

                   boolean isEmpty = rollNo == null || rollNo.trim().length() == 0;

                   //if (isEmpty)

                     // break;

                    try{

                          System.out.println("Comes Here1");

                           //STEP 2: Register JDBC driver

                           Class.forName("com.mysql.jdbc.Driver");

                           //STEP 3: Open a connection

                           System.out.println("Connecting to database...");

                           conn = DriverManager.getConnection(DB_URL,USER,PASS);

                           //STEP 4: Execute a query

                           System.out.println("Creating statement Testing 999 ..." + rollNo);

                           String sql;

                           sql = "Create table if not exists " + newRollNo+ " (id INTEGER not null primary key auto_increment, name varchar(30),  totalTheoryClasses INTEGER, totalLabs INTEGER, WeekNo INTEGER, DaysPresent INTEGER, DaysAbset INTEGER, Percentage FLOAT)";

                          

                           stmt = conn.createStatement();

                          

                          

                           //sql ="Create table if not exists Test(id Integer)";

                          

                            stmt.executeUpdate(sql);

                            System.out.println("Comes Here Testing 110");

                        }

                        catch(SQLException sqle) {

System.out.println("Error1 after modifying");

sqle.printStackTrace();

                       

                        }

                        catch(ClassNotFoundException cnfe) {

System.out.println("Error2");

                        }

                        catch (Exception e) {

System.out.println("Error3");

                        }

                        finally{

                           try{

                                 if(conn!= null)

                                 conn.close();

                               }

                       

                        catch(SQLException sqle) {

System.out.println("Error4");

                        }

                       }//finally

//                     }//for

                  

                   //System.out.println("rollNo" + rollNo);

                  

               

               

                //System.out.print(sh.getCell(col, row).getContents() + "\t");

/*for (int row = 0; row < totalNoOfRows; row++) {

for (int col = 0; col < totalNoOfCols; col++) {

System.out.print(sh.getCell(col, row).getContents() + "\t");

}

System.out.println();

}*/

    }

    public static void main(String[] args)throws BiffException, IOException {

        // TODO code application logic here

        ReadExcelSheetMain6 obj = new ReadExcelSheetMain6();

        obj.readExcel();

    }

   

}

I check the documentation under prepared statement but i cant find that prepared statement can not be allowed on create table query. Even stackoverflows provide its solutions. 

Problem Solved.Thanks.

Zulfi.

unknown-7404

I check the documentation under prepared statement but i cant find that prepared statement can not be allowed on create table query.

That is NOT what I said - reread my reply.

I said that table names can NOT be used for bind variables. You need to construct a query that has the table name already in it - you can't use a 'setXXX' statement to alter the table name.

I am keeping each students' record in a separate table.

That is what I meant when I said you are likely using the wrong data model.

You should keep like data in the same table. One table to hold rows for ALL students.

By using that correct data model your problem goes away - there is only ONE table name to remember and only one table to query.

mNem

Do a google search for "student attendance database" images. Should give you some idea.

Try to produce some queries with your design on paper first.

mNem

Try not to leave commented out code blocks in the methods. Keep it clean. It helps.

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Locked on Apr 27 2007
Added on Mar 30 2007
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