plpgsql 中 WHILE 循环"END LOOP;"部分的语法错误

Question

我在尝试在 plpgsql 中定义我无法解释的函数时遇到语法错误。由于某种原因，此代码将始终失败，并显示syntax error at or nor "LOOP"：

CREATE OR REPLACE FUNCTION ST_Dilate(
    in_geom GEOMETRY,
    scale_factor FLOAT,
    tol FLOAT DEFAULT 0.001,
    guess FLOAT DEFAULT 1,
    safety INTEGER DEFAULT 1000
)
RETURNS GEOMETRY AS
$$
DECLARE
    step FLOAT = guess/2;
    current_area FLOAT = ST_Area(ST_Buffer(in_geom, buff));
    desired_area FLOAT = ST_Area(in_geom)*scale_factor;
    dev FLOAT = (current_area-desired_area)/desired_area;
    old_dev FLOAT;
    safety_counter INTEGER = 0;
BEGIN
    WHILE ABS(dev) > tol LOOP
        IF safety_counter > safety THEN /* Can't find suitable distance after many iterations, terminate the function to prevent extreme hangs. */
            RAISE NOTICE 'Could not find suitable buffer distance when dilating geom % after % iterations, NULL geometry returned instead. Consider adjusting "guess" parameter value or initial step size.', geom, safety;
            RETURN NULL;
        END IF;
        safety_counter = safety_counter + 1;
        /* Save the old deviation to be compared later to the new one later, calculate the current area and the new deviation from the desired area. */
        old_dev = dev;
        current_area = ST_Area(ST_Buffer(in_geom, guess));
        dev = (current_area - desired_area) / desired_area;
        IF dev < 0 THEN /* Current area is smaller than desired area, increase the buffer distance by the step. */
            guess = guess + step;
        ELSE IF dev > 0 THEN /* Current area is larger than desired area, decrease the buffer distance by the step. */
            guess = guess - step;
        ELSE /* Technically shouldn't ever happen because then ABS(dev) is indeed lesser than tol but here just in case. */
            EXIT;
        END IF;
        IF dev * old_dev < 0 THEN /* Negative value indicates difference of sign, which means we just overestimated the area after underestimating it or vice versa, need to half the step. */
            step = step * 0.5;
        END IF;
    END LOOP; /* syntax error here */
    RETURN ST_Buffer(in_geom, guess);
END
$$
LANGUAGE plpgsql;

我根本没有看到语法错误。更令人困惑的是，如果我注释掉这个块：

IF safety_counter > safety THEN /* Can't find suitable distance after many iterations, terminate the function to prevent extreme hangs. */
            RAISE NOTICE 'Could not find suitable buffer distance when dilating geom % after % iterations, NULL geometry returned instead. Consider adjusting "guess" parameter value or initial step size.', geom, safety;
            RETURN NULL;
        END IF;
        safety_counter = safety_counter + 1;

代码成功执行一次，但第二次立即失败并出现相同的错误。

我对此完全感到困惑。我已经一次注释掉了每个块以及试图找到问题的单个行，我在任何地方都找不到语法错误，但它一直在抱怨。

我在 postgresql 9.6 上。

Answer 1

如果要获取单个IF语句，请使用ELSIF：

    IF dev < 0 THEN /* Current area is smaller than desired area, increase the buffer distance by the step. */
        guess = guess + step;
    ELSIF dev > 0 THEN /* Current area is larger than desired area, decrease the buffer distance by the step. */
        guess = guess - step;
    ELSE /* Technically shouldn't ever happen because then ABS(dev) is indeed lesser than tol but here just in case. */
        EXIT;
    END IF;

阅读有关控制结构的文档。

Answer 2

你在END LOOP之前错过了END IF。看到它简化和预期：

    IF dev < 0 THEN
        guess = guess + step;
    ELSE 
        IF dev > 0 THEN
            guess = guess - step;
        ELSE
            EXIT;
        END IF;
    END IF; -- this is missing