Setting Join Tables

Setting join fields enhances the information of current datasets, facilitating SQL queries and SQL condition construction. The Join Attributes dialog box contains the following parameters:

  • External Table: The dataset associated with the current (source) dataset properties table. Click the cell's drop-down menu to select a dataset from the current workspace as the relation.
  • Field: A field in the source dataset properties table used to establish relationships with external tables.
  • Join Field: A field in the relation attribute table used to establish relationships with the source dataset.
  • Expression: Displays the join condition between the source dataset properties table and the relation attribute table. The connection condition will be automatically generated after setting fields and join fields.
  • Type: Supports two join types: Left Join and Inner Join.
    • Left Join: The number of valid records after joining equals the source dataset. Available field values include all fields from the source dataset and matched fields from the relation.
    • Inner Join: The number of valid records after joining equals the fully matched records between the source dataset and relation. Available field values include only fully matched fields from both datasets.
      Field Field 2
      1 1A
      2 2B
      3 3C
      4 4D
      Join Field Field 3
      1 10
      2 20
      3 30
      5 50
      Join Field Field 2 Field 3
      1 1A 10
      2 2B 20
      3 3C 30
      4 4D  
      Join Field Field 2 Field 3
      1 1A 10
      2 2B 20
      3 3C 30
           
      Source Dataset Table
      Relation Attribute Table
      Left Join Search Result
      Inner Join Search Result
  • Rule: When adding multiple join conditions for the same external table, double-click the Rule cell of a previous record to set its logical relationship with subsequent conditions via the drop-down button. Provides AND and OR rules:
    • AND: Set rule to AND when requiring all conditions to be satisfied.
    • OR: Set rule to OR when requiring any condition to be satisfied.

     

Notes:
  • It is recommended that the join fields (Field and Join Field) be of integer type and indexed.
  • For PostGIS datasets with external join tables, the system will automatically add quotes to table names when building query expressions to resolve case sensitivity issues in databases.

Related Topics

Build SQL Query

Construct SQL Expression Query

SQL Query Function Specifications

Attribute Query Example

Group Statistics Example