Query Layer

The Query Layer interface is used to define a query expression and the color used to highlight the selected objects obtained when the query is applied. A query expression is defined by a restriction clause (WHERE clause).

LAYER EXPLORER → right click over an layer name → QUERY


This interface consists of the following steps:

Input Layer - Select the input layer.

Criteria - Defines the Restriction Clause.

Layer Selection options:

Add: Transforms the query result in the layer selected items, adding the query results to the layer selection.

New: Transforms the query result in the layer selected items and remove previous layer selection.

None: The result will be just painted over the map.

Highlight: Sets the color to be used to highlight the selected objects.

WHERE clause

The WHERE clause Interface is used to define the restriction used to generate a new dataset. The restriction can involve one or more datasets, using standard and/or spatial attributes (vertical tabs). The list of operators supported is adjusted to the type of attributes involved.

The operators <,>,<=,>=,<>,=, LIKE, NOT are used with standard attributes comparison, and the spatial operators such as ST_UNION, ST_INTERSECTION, ST_AREA among others are used to operate over geometric attributes.

To define a restriction based on Attributes follow the steps:

Select restriction type on the vertical Attribute tab:


Define a restriction by selecting:

Property

Operator - (>, >=, <, <=, = )

Value - it can be a property of other dataset or a value among all values of the property chosen (Property or Value).

Click on icon to add this combination (property x operator x value) to the Table/SQL tabs bellow.

On the frame Table/SQL it is possible to handle the restriction adding more clauses, removing one or all lines, or checking the SQL generated:

Check the list of restrictions.

Define the connector (and, or, nothing) and the next restriction.

Clear all restriction using or only one line using .

Optionally, change to SQL tab to see the restriction generated in SQL.

Repeat the steps to define the next part of the restriction as necessary.


To define a restriction based on spatial attributes follow the steps:


Select Spatial vertical tab:

Define a restriction by selecting:

Property - geometry attribute of the selected dataset.

Operator - (ST_Contains, ST_Union, ST_Crosses, …).

Layer - select the layer to be confronted with the restriction defined.

Use Selected Objects - check this option if the goal is to apply the restriction only over the selected objects in the layer displayed.

Click on to add this combination (property x operator x value) to the Table/SQL tabs bellow.

On the frame Table/SQL it is possible to handle the restriction adding more clauses, removing or checking the SQL generated:

Check the list of restrictions.

Define the connector (and, or, nothing) and the next restriction.

Clear all restriction using or only one line using .

Optionally, change to SQL tab to see the restriction generated in SQL.

Repeat the steps to define the next part of the restriction as necessary.