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  • Data Manipulation Language

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    These statement consist of queries that retrieve data from tables in database and statements that change the data in the database

    Statement under this category are:

    SELECT

    INSERT

    UPDATE

    DELETE

    LOCK TABLE etc.

    Insert command

    It is used to add rows to a table.

    INSERT INTO TABLE-NAME VALUES (data value 1,data value 2);

    The number and sequence of data values should match that of column in the table. If number of data values less, then specify the column names into which data is being entered as illustrated.

    INSERT INTO TABLE-NAME(column 1, column 3)

    To insert null values, NULL may be used

    INSERT INTO EMP VALUES(1001,'sharma',NULL.NULL3000,NULL)

    Queries

    Query has following two components:

    1.SELECT clause.

    It lists name of columns containing the required data specifies the table in which these columns are located.

    2.FROM clause.

    It can also specify operations to be performed on the data and displays the result of these operations. Results of the query is displayed in a table form and is sometimes called  result table. The rows in the result represent the data that meet the conditions; if no data qualifies, zero rows are selected.

    Narrowing the query : WHERE clause

    It narrow scope of the query by focusing on selected rows.

    e.g.

    SELECT     NAME,TRAINER

    FROM         GUEST-ROSTER

    WHERE     TRAINER="TODD";

                                     NAME                                        TRAINER

                                     SEAN PENCIL                            TODD

                                     DON JACKSON                          TODD

                                    DIANCA JOGGER                       TODD

    Relational predicates: TRAINER ="TODD"

    '=' is a simple relational operator.

    There are nine simple relational operators:

     =      is equal to

     !=     is not equal to

    <>     is not equal to

    >    is greater than

    !>     is not greater than

    <     is less than

    !<     is not less than

    >=     is greater than or equal to

    <=    is less than or equal to

    Other relational predicates

    These are four other relational operators that can be used to form relational predicates:

    BETWEEN...AND

    IS NULL

    IN

    EXIST

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