Page 335 - IT 402 v2.0 class 10
P. 335

+ - - - - - - +
                                                           |  CO ST  |
                                                           + - - - - - - +
                                                           |    2 0  |
                                                           |    1 0  |
                                                           |    4 5  |
                                                           |   1 2 0  |
                                                           |    3 0  |
                                                           + - - - - - - +
               UPDATING RECORDS IN A TABLE

            Sometime, you may need to change the detail inserted into a table. In that case, the UPDATE command will
            work. The syntax of the UPDATE command is:

                   table name S   field change value       field criteria value
            Let us change the marks of the student having 10002 as StudentID from 480 to 485 by using the following
            command:

              U P D AT E  Stu d ent SE T  M ar k s =  4 8 5  w her e Stu d entI D  =  1 0 0 0 2 ;
                                   + - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - +
                                   |  Stu d entI D  |  F ir stName |  L astName |  M ar k s |
                                   + - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - +
                                   |      1 0 0 0 1  |  Amit      |  Shar ma   |    4 5 0  |
                                   |      1 0 0 0 2  |   D iv y a    |  K au shik   |    4 8 5  |
                                   |      1 0 0 0 3  |   Aad ar sh  |  K u mar     |    4 5 0  |
                                   + - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - +
               REMOVING RECORDS FROM A TABLE

            The DELETE command is used to remove records from a table. The DELETE command can be used in two
            ways:
              Without WHERE clause                              With the WHERE clause


             e can remove a specific record by using the       clause with the        command. If we use the
            command without the WHERE clause, it will remove all the records from a table. Let us use the DELETE
            command to remove the record of a student whose LastName is Kumar:
                   F OM Student        astName   umar

            To remove all the records, following command is used:
            DELETE FROM Student;

               USING AGGREGATE FUNCTIONS WITH SELECT COMMAND

            MySQL provides the following aggregate functions:

                     Function                                       Description
                                     It calculates the average of the values in the selected column.
                  O N                It calculates the number of rows returned for a SELECT command.
                 M                   It calculates the maximum value from a column.

                 MIN                 It calculates the minimum value from a column.
                 S M                 It calculates the sum of the values in a specified column.




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