我试图弄清楚如何在函数中进行任意计算并相应地更新true/false变量：

DROP TABLE IF EXISTS conditions;

CREATE TABLE conditions(
    id SERIAL PRIMARY KEY,
    val_1 INT NOT NULL,
    operator_1 TEXT,
    val_2 INT,
    comparison_operator TEXT NOT NULL,
    val_3 INT NOT NULL,
    operator_2 TEXT,
    val_4 INT,
    current_state BOOL,
    CONSTRAINT c1 CHECK ((val_2 IS NULL AND operator_1 IS NULL) OR (val_2 IS NOT NULL AND operator_1 IS NOT NULL)),
    CONSTRAINT c2 CHECK ((val_4 IS NULL AND operator_2 IS NULL) OR (val_4 IS NOT NULL AND operator_2 IS NOT NULL))
);

CREATE OR REPLACE FUNCTION do_calculation()
RETURNS TRIGGER AS $$
BEGIN   
/*
    UPDATE conditions
    SET current_state = ...???
*/
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER calculate
    AFTER INSERT OR UPDATE ON conditions
    FOR EACH ROW
    EXECUTE PROCEDURE do_calculation();

INSERT INTO conditions (val_1, comparison_operator, val_3) VALUES (1, '>', 2);
INSERT INTO conditions (val_1, operator_1, val_2, comparison_operator, val_3) VALUES (1, '+', 3, '>', 2);
INSERT INTO conditions (val_1, operator_1, val_2, comparison_operator, val_3, operator_2, val_4) VALUES (1, '+', 3, '=', 2, '*', 2);
UPDATE conditions SET val_1 = 3 WHERE id = 1;

SELECT * FROM conditions;

但是如何在do_calculation（）函数中进行实际计算呢？