下面是SELECT语句的逻辑执行顺序：
FROM
ON
JOIN
WHERE
GROUP BY
WITH CUBE or WITH ROLLUP
HAVING
SELECT
DISTINCT
ORDER BY
TOP
几个示例
第一个示例
SELECT ID,COUNT(ID) AS TOTAL
FROM STUDENT
GROUP BY ID
HAVING TOTAL>2
实际执行顺序如下：
FROM STUDENT
GROUP BY ID
HAVING TOTAL>2
SELECT ID,COUNT(ID) AS TOTAL
TOTAL是在最后一句SELECT ID,COUNT(ID) AS TOTAL执行过后生成的新别名。因此，在HAVING TOTAL>2执行时是不能识别TOTAL的。
第二个示例
SELECT ID,COUNT(ID) AS TOTAL
FROM STUDENT
GROUP BY ID
ORDER BY TOTAL
实际执行顺序是：
FROM STUDENT
GROUP BY ID
SELECT ID,COUNT(ID) AS TOTAL
ORDER BY TOTAL
第三个示例
SELECT ID,COUNT(ID) AS TOTAL
FROM STUDENT
GROUP BY ID
ORDER BY COUNT(ID)
实际执行顺序：
FROM STUDENT
GROUP BY ID
SELECT ID,COUNT(ID) AS TOTAL
ORDER BY COUNT(ID)
第四个示例
SELECT FIRSTNAME+’ ‘+LASTNAME AS NAME, COUNT(*) AS COUNT
FROM STUDENT
GROUP BY NAME
实际执行顺序：
FROM STUDENT
GROUP BY NAME
SELECT FIRSTNAME+’ ‘+LASTNAME AS NAME,COUNT(*) AS COUNT