GROUP_CONCAT
语法：
GROUP_CONCAT([DISTINCT] expr1 [, expr2...] [ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [, col_name...]] [SEPARATOR str_val])
功能：分组进行字符串连接，并在连接时用指定的分隔符隔开。
说明：
如果用户指定了两个及以上表达式，则该函数在分组进行字符串连接之前会先将指定的多个表达式进行字符串连接，但此时的连接并没有任何分隔符。
默认的分隔符为逗号","。
函数多支持64个参数，GROUP_CONCAT函数的分隔符占用一个参数，实际大支持63个参数。
示例：
按staff_ID分组，连接SALARY的值。
CREATE TABLE staffS
(
staff_ID NUMBER(6) not null,
FIRST_NAME VARCHAR2(20),
LAST_NAME VARCHAR2(25),
EMAIL VARCHAR2(25),
PHONE_NUMBER VARCHAR2(20),
HIRE_DATE DATE,
employment_ID VARCHAR2(10),
SALARY NUMBER(8,2),
COMMISSION_PCT NUMBER(2,2),
MANAGER_ID NUMBER(6),
section_ID NUMBER(4)
);
INSERT INTO staffs (staff_ID, FIRST_NAME, LAST_NAME, EMAIL, PHONE_NUMBER, HIRE_DATE, employment_ID, SALARY, COMMISSION_PCT, MANAGER_ID, section_ID)
VALUES (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK', 2600.00, null, 124, 50);
INSERT INTO staffs (staff_ID, FIRST_NAME, LAST_NAME, EMAIL, PHONE_NUMBER, HIRE_DATE, employment_ID, SALARY, COMMISSION_PCT, MANAGER_ID, section_ID)
VALUES (199, 'Douglas', 'Grant', 'DGRANT', '650.507.9844', to_date('13-01-2000', 'dd-mm-yyyy'), 'SH_CLERK', 2600.00, null, 124, 50);
INSERT INTO staffs (staff_ID, FIRST_NAME, LAST_NAME, EMAIL, PHONE_NUMBER, HIRE_DATE, employment_ID, SALARY, COMMISSION_PCT, MANAGER_ID, section_ID)
VALUES (200, 'Jennifer', 'Whalen', 'JWHALEN', '515.123.4444', to_date('17-09-1987', 'dd-mm-yyyy'), 'AD_ASST', 4400.00, null, 101, 10);
INSERT INTO staffs (staff_ID, FIRST_NAME, LAST_NAME, EMAIL, PHONE_NUMBER, HIRE_DATE, employment_ID, SALARY, COMMISSION_PCT, MANAGER_ID, section_ID)
VALUES (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK', 2600.00, null, 124, 50);
SELECT staff_ID,GROUP_CONCAT(SALARY) FROM staffs GROUP BY staff_ID;
STAFF_ID GROUP_CONCAT(SALARY)
---------------------------------------- ----------------------------------------------------------------
200 4400
198 2600,2600
199 2600
3 rows fetched.
