HAVING 子句使你能夠指定過濾條件,從而控制查詢結果中哪些組可以出現在最終結果里面。
WHERE 子句對被選擇的列施加條件,而 HAVING 子句則對 GROUP BY 子句所產生的組施加條件。
下面可以看到 HAVING 子句在 SELECT 查詢中的位置:
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY
在 SELECT 查詢中,HAVING 子句必須緊隨 GROUP BY 子句,并出現在 ORDER BY 子句(如果有的話)之前。帶有 HAVING 子句的 SELECT 語句的語法如下所示:
SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2
考慮 CUSTOMERS 表,表中的記錄如下所示:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
下面是一個有關 HAVING 子句使用的實例,該實例將會篩選出出現次數大于或等于 2 的所有記錄。
SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY
FROM CUSTOMERS
GROUP BY age
HAVING COUNT(age) >= 2;
其執(zhí)行結果如下所示:
+----+--------+-----+---------+---------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+--------+-----+---------+---------+
| 2 | Khilan | 25 | Delhi | 1500.00 |
+----+--------+-----+---------+---------+