postgreSQL 中的复制约束使用（使用 GIST 和或 EXCLUDE）

Question

How to write a constraint (table level unique, using GIST and or EXCLUDE ) to perform duplication record validation using the following rule:

1. Entered from_date and to_date values should not be equal or within the range, and
2. Employee_id should not be equal, and
3. status = 'pending'

After the validation, an error message should be return saying 'Duplicate Entry'. This is in postgreSQL.

Note: I am new to postgreSQL (worked in MS SQL Server and MySQL).

Thanks in advance.

Answer 1

As stated by @Laurenz Albe, it sounds like impossible to do with a constraint. You can implement either a trigger function or a rule instead :

Trigger function :

CREATE OR REPLACE FUNCTION test_insert_table()
RETURNS trigger LANGUAGE plpgsql IMMUTABLE AS
$$
BEGIN
IF NEW.status = 'pending'
AND EXISTS
  ( SELECT 1
      FROM your_table
     WHERE Employee_id = NEW.Employee_id
       AND range @> daterange(NEW.from_date, NEW.to_date)
  )
THEN
  RAISE EXCEPTION 'Duplicate Entry' ;
  RETURN NULL ;
ELSE
  RETURN NEW ;
END IF ;
END ;
$$

CREATE OR REPLACE TRIGGER test_insert_table 
BEFORE INSERT ON your_table
FOR EACH ROW EXECUTE FUNCTION test_insert_table() ;

Rule :

CREATE OR REPLACE RULE test_insert AS
    ON INSERT TO your_table
 WHERE NEW.status = 'pending'
   AND EXISTS
       ( SELECT 1
           FROM your_table
          WHERE Employee_id = NEW.Employee_id
            AND range @> daterange(NEW.from_date, NEW.to_date)
       )
    DO INSTEAD NOTHING ;