About-Database-Queries

About Database Queries

    About Database Queries

    Part of the fundamental power of database systems is their ability to present a subset
    of records based on a search criterion or query that you specify. For example, you might have a database table containing records
    of all the rooms that exist at your company’s headquarters facilities. Suppose that
    you want to prepare a report that lists all conference rooms that can seat more than
    20 people. Using the Query Editor, you can easily construct a query that returns the
    subset of records or linked graphical objects that you want to see.

    The Query Editor consists of a series of four tabs that you can use to develop queries.
    The tabbed progression is designed to make working with queries simple, even if you
    are not familiar with Structured Query Language (SQL). If you are unfamiliar with
    queries, work with the Quick Query and Range Query tabs initially until you become
    familiar with query syntax. Once you learn the basics involved in developing meaningful
    queries, you can progress to the Query Builder and SQL Query tabs.

    You can begin creating a query in one tab and continue to refine it or add additional
    parameters in subsequent tabs. You might, for example, begin creating a simple query
    in the Quick Query tab and subsequently decide that you would like to add an additional
    condition using the Query Builder tab. When you click the Query Builder tab, it displays
    the values that you initially selected using the Quick Query tab, and you can add
    additional conditions to the query. However, you cannot move backwards through the
    tabs once you have changed the query in one of the later tabs, because each subsequent
    tab provides additional functions that are not available in the previous tabs. If
    you attempt to move backwards through the query tabs after modifying a query, you
    are prompted with a warning indicating that the query will be reset with its original
    default values.

    The tabbed progression of the Query Editor is particularly useful in becoming familiar
    with SQL syntax. For example, you can create a query using the Quick Query tab and
    then select the SQL Query tab to view how your query is formatted using SQL.

    The Query Editor provides the following tabs for building queries:

    • Quick Query. Provides an environment where you can develop simple queries based on a single database
      field, single operator, and single value. For example, you can find all records from
      the current database table where the value of the “room type” field equals “office.”

    • Range Query. Provides an environment where you can develop a query that returns all records that
      fall within a given range of values. For example, you can find all records from the
      current database table where the value of the “room area” field is greater than or
      equal to 90 square feet and less than or equal to 120 square feet.
    • Query Builder. Provides an environment where you can develop more complicated queries based on
      multiple search criteria. For example, you can find all records from the current database
      table where the “room type” equals “cubicle” and room area is greater than 80 square
      feet.
    • SQL Query. Provides an environment where you can develop sophisticated queries that conform
      with the SQL 92 protocol. For example, you can select * from california.headquarters.room
      where

      california.headquarters.room.type = ‘cubicle’

      and

      california.headquarters.room.area < 80.

    See To Work With Simple Queries for detailed information about constructing queries
    and working with operators. If you are already comfortable building database queries,
    see To Work with the Query Builder.

    Learning AutoCad

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