postgresql 函数根据 IF ELSEIF 条件更新每一行

Question

我正在尝试创建一个将由 cron 作业每 30 分钟执行一次的 postgresql 函数。此函数将执行 if else 条件并根据当前时间和其他列值更新列。

我总是在 IF 语句的开头遇到语法问题，无法理解为什么：

ERROR:  syntax error at or near "scheduled_active_start"
LINE 7:      IF scheduled_active_start <= executionTime AND schedule...
                ^
********** Error **********

ERROR: syntax error at or near "scheduled_active_start"
SQL state: 42601
Character: 144

这是我要创建的 postgresql 函数：

CREATE OR REPLACE FUNCTION updatePostActivity()   RETURNS void AS $$

DECLARE
    executionTime timestamp = Now();
BEGIN
    UPDATE  post
        IF scheduled_active_start <= executionTime AND scheduled_active_end > executionTime AND is_active != true THEN
             SET is_active = true;
        ELSEIF  scheduled_active_end <= executionTime AND is_active != false THEN 
            SET is_active = false;
        END IF;
END;
$$   
LANGUAGE plpgsql VOLATILE

Answer 1

UPDATE statement clearly stays that there is nothing between UPDATE and SET keywords except the table definition. The IF statement is absent in the SQL at all (as I know). Use CASE 语句的语法改为：

UPDATE post SET
  is_active = CASE 
    WHEN scheduled_active_start <= executionTime AND scheduled_active_end > executionTime AND is_active != true THEN true
    WHEN scheduled_active_end <= executionTime AND is_active != false THEN false
  END
WHERE -- Filter to avoid updating whole table
  (scheduled_active_start <= executionTime AND scheduled_active_end > executionTime AND is_active != true) OR
  (scheduled_active_end <= executionTime AND is_active != false);

PS：is_active != true 等于 not is_active，is_active != false 等于 is_active

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