Use Queries to Filter Database Information

Use Queries to Filter Database Information

Construct Simple Queries

 

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Overview of Queries

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Concept

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Quick Reference

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