在SQL語句中，EXISTS是一個用于檢查子查詢是否返回結果的條件運算符。它可以在WHERE子句中使用，也可以在SELECT語句中使用。
SELECT column1, column2, ...
FROM table_name
WHERE EXISTS (SELECT column1 FROM table_name WHERE condition);
SELECT column1, column2, ...
FROM table_name1
WHERE EXISTS (SELECT column1 FROM table_name2 WHERE condition);
INSERT INTO table_name (column1, column2, ...)
SELECT value1, value2, ...
FROM table_name2
WHERE EXISTS (SELECT column1 FROM table_name2 WHERE condition);
UPDATE table_name1
SET column1 = value1, column2 = value2, ...
WHERE EXISTS (SELECT column1 FROM table_name2 WHERE condition);
