Lab 7: Attribute SQL- Query the database

You have been asked to determine which parcel properties have a marketvalue greater than $75,000. You have been asked to find these properties and display on a mapwithin your study area.

How will you find the properties & display on a map using MapInfo?

In this lesson, you will learn how to ask questions/ query the attributetable data using query menus to build SQL (structured query language).

You will also learn what a relational join is and how to perform a relational join.

To query data in MapInfo, use Query> Select for simple selections:In this example, we want to find Census blocks that have >= 100 persons

1 First select File> open table

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2 Select Query> Select

3 Select table

4 Select assistto write query

5 Select the column “population”6 Select the operator “>=“7 Type the value “100”8 Verify the syntax9 Select Ok10 Select OK to find the answer (next Slide)

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The Query > Select result in parcels with “population >= 100” displays as a browser and each block highlighted on the map.The query results can be saved as a new table, discarded, or

the syntax can be saved in a query template.

To query data in MapInfo, use Query> SQL Select for more complex selections.Shown below is the Query> SQL Select screen example from MapInfo with a brief description of the options.

Select File>Open> select table, select Query> SQL Select 1a Highlight From Tables box

1b Select table from tables pop up (table appears in From Tables box) 2a Move cursor to where Condition box; 2b Select column required from columns menu pop up & the column (totalpopulation) displays in the where condition window3 Select operator (=,>,<,*,/,etc) from Operators menu pop up (operator appears in where condition)4 Type the value in the where condition box (In this case- 25000)5 Select other options (Here we are sorting by field totalpopulation so select Order by columns, select the columns button and select the column to sort by6 Select Ok – The results of the query are displayed as records in a browser & highlighted on map (See results on next Slide)

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The results of the Query>SQL Select– cities where the total population is <= 25,000:

A browser called Query1 is created that meets the SQL conditions (48 cities) and a map showing the 48 cities are highlighted

Also, note that the cities are sorted in ascending (increasing) value by total population

A common relational join using Query> SQL Select in MapInfo:Join the parcel polygon file to the Auditor’s parcel characteristics table.

1. Open the tables that you wish join

2 Determine the fields that are a common link

Relational Join – MapInfo example (continued)

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3 Select Query> SQL Select4 Select tables to join5 type where condition or choose from column button parcel.ppn choose operator button = from column button audattr.parcel6 Verify syntax7 Select OK8 Query runs: results in a browser and polygons highlighted that met requirements. Query 1 can then be saved to a new table.

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You are now ready to begin MapInfo Exercise- Lab 7Attribute SQL. The main objectives are:

• To ask questions or query the attribute table using:

Query> Select Menu (for simple questions) Query> SQL Select Menu (complex questions)

• Begin exercise- lab 7