{"id":219,"date":"2021-08-11T11:03:06","date_gmt":"2021-08-11T03:03:06","guid":{"rendered":"https:\/\/9iwd.top\/?p=219"},"modified":"2021-08-11T11:03:07","modified_gmt":"2021-08-11T03:03:07","slug":"no8-mysql-%e5%88%86%e7%bb%84%e5%87%bd%e6%95%b0","status":"publish","type":"post","link":"http:\/\/9iwd.top\/?p=219","title":{"rendered":"No8 mysql \u5206\u7ec4\u51fd\u6570"},"content":{"rendered":"\n<pre class=\"wp-block-code\"><code>\u8ba1\u6570 : count\r\n\u6c42\u548c : sum\r\n\u5e73\u5747\u503c : avg\r\n\u6700\u5c0f\u503c : min\r\n\u6700\u5927\u503c : max\r\n\r\n\u6ce8\u610f\uff1a\r\n\t\u5206\u7ec4\u51fd\u6570\u5728\u4f7f\u7528\u7684\u65f6\u5019\u5fc5\u987b\u5148\u8fdb\u884c\u5206\u7ec4\uff0c\u7136\u540e\u624d\u80fd\u7528\u3002\r\n\t\u5982\u679c\u4f60\u6ca1\u6709\u5bf9\u6570\u636e\u8fdb\u884c\u5206\u7ec4\uff0c\u6574\u5f20\u8868\u9ed8\u8ba4\u4e3a\u4e00\u7ec4\u3002<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u6240\u6709\u8bb0\u5f55\nmysql> select * from emp;\r\n+-------+--------+-----------+------+------------+---------+---------+--------+\r\n| EMPNO | ENAME  | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |\r\n+-------+--------+-----------+------+------------+---------+---------+--------+\r\n|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |    NULL |     20 |\r\n|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |\r\n|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |\r\n|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |    NULL |     20 |\r\n|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |\r\n|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |\r\n|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |    NULL |     10 |\r\n|  7788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 | 3000.00 |    NULL |     20 |\r\n|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 |    NULL |     10 |\r\n|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |\r\n|  7876 | ADAMS  | CLERK     | 7788 | 1987-05-23 | 1100.00 |    NULL |     20 |\r\n|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |\r\n|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |    NULL |     20 |\r\n|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |    NULL |     10 |\r\n+-------+--------+-----------+------+------------+---------+---------+--------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u6700\u5927\u503c : max\r\n\/\/\u627e\u51fa\u6700\u9ad8\u5de5\u8d44\uff1f\nmysql> select max(sal) from emp;\r\n+----------+\r\n| max(sal) |\r\n+----------+\r\n|  5000.00 |\r\n+----------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u6700\u5c0f\u503c : min\r\n\/\/\u627e\u51fa\u6700\u4f4e\u5de5\u8d44\uff1f\nmysql> select min(sal) from emp;\r\n+----------+\r\n| min(sal) |\r\n+----------+\r\n|   800.00 |\r\n+----------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u6c42\u548c : sum\r\n\/\/\u8ba1\u7b97\u5de5\u8d44\u548c\nmysql> select sum(sal) from emp;\r\n+----------+\r\n| sum(sal) |\r\n+----------+\r\n| 29025.00 |\r\n+----------+\n<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u5e73\u5747\u503c : avg\r\n\/\/\u8ba1\u7b97\u5e73\u5747\u5de5\u8d44\nmysql> select avg(sal) from emp;\r\n+-------------+\r\n| avg(sal)    |\r\n+-------------+\r\n| 2073.214286 |\r\n+-------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u8ba1\u6570 : count\r\n\/\/\u8ba1\u7b97\u5458\u5de5\u6570\u91cf\uff1f\nmysql> select count(ename) from emp;\r\n+--------------+\r\n| count(ename) |\r\n+--------------+\r\n|           14 |\r\n+--------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u5206\u7ec4\u51fd\u6570\u5728\u4f7f\u7528\u7684\u65f6\u5019\u9700\u8981\u6ce8\u610f\u54ea\u4e9b\uff1f\n\/\/\u7b2c\u4e00\u70b9\uff1a\u5206\u7ec4\u51fd\u6570\u81ea\u52a8\u5ffd\u7565NULL\uff0c\u4f60\u4e0d\u9700\u8981\u63d0\u524d\u5bf9NULL\u8fdb\u884c\u5904\u7406\u3002\nmysql> select sum(comm) from emp;\r\n+-----------+\r\n| sum(comm) |\r\n+-----------+\r\n|   2200.00 |\r\n+-----------+\n\nmysql> select count(comm) from emp;\r\n+-------------+\r\n| count(comm) |\r\n+-------------+\r\n|           4 |\r\n+-------------+\n\nmysql> select avg(comm) from emp;\r\n+------------+\r\n| avg(comm)  |\r\n+------------+\r\n| 550.000000 |\r\n+------------+\n\n\/\/\u7b2c\u4e8c\u70b9\uff1a\u5206\u7ec4\u51fd\u6570\u4e2dcount(*)\u548ccount(\u5177\u4f53\u5b57\u6bb5)\u6709\u4ec0\u4e48\u533a\u522b\uff1f\nmysql>  select count(*) from emp;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n|       14 |\r\n+----------+\n\nmysql> select count(comm) from emp;\r\n+-------------+\r\n| count(comm) |\r\n+-------------+\r\n|           4 |\r\n+-------------+\n\n\/\/count(\u5177\u4f53\u5b57\u6bb5)\uff1a\u8868\u793a\u7edf\u8ba1\u8be5\u5b57\u6bb5\u4e0b\u6240\u6709\u4e0d\u4e3aNULL\u7684\u5143\u7d20\u7684\u603b\u6570\u3002\n\/\/count(*)\uff1a\u7edf\u8ba1\u8868\u5f53\u4e2d\u7684\u603b\u884c\u6570\u3002\uff08\u53ea\u8981\u6709\u4e00\u884c\u6570\u636ecount\u5219++\uff09\n\/\/\u56e0\u4e3a\u6bcf\u4e00\u884c\u8bb0\u5f55\u4e0d\u53ef\u80fd\u90fd\u4e3aNULL\uff0c\u4e00\u884c\u6570\u636e\u4e2d\u6709\u4e00\u5217\u4e0d\u4e3aNULL\uff0c\u5219\u8fd9\u884c\u6570\u636e\u5c31\u662f\u6709\u6548\u7684\u3002\n\n\n\/\/\u7b2c\u4e09\u70b9\uff1a\u5206\u7ec4\u51fd\u6570\u4e0d\u80fd\u591f\u76f4\u63a5\u4f7f\u7528\u5728where\u5b50\u53e5\u4e2d\u3002\n\/\/\u627e\u51fa\u6bd4\u6700\u4f4e\u5de5\u8d44\u9ad8\u7684\u5458\u5de5\u4fe1\u606f\u3002\nselect ename,sal from emp where sal > min(sal);\n\/\/\u8868\u9762\u4e0a\u6ca1\u95ee\u9898\uff0c\u8fd0\u884c\u4e00\u4e0b\uff1f\nERROR 2013 (HY000): Lost connection to MySQL server during query  ?\n\/\/\u8bf4\u5b8c\u5206\u7ec4\u67e5\u8be2(group by)\u4e4b\u540e\u5c31\u660e\u767d\u4e86\u4e86\u3002\n\n\n\/\/\u7b2c\u56db\u70b9\uff1a\u6240\u6709\u7684\u5206\u7ec4\u51fd\u6570\u53ef\u4ee5\u7ec4\u5408\u8d77\u6765\u4e00\u8d77\u7528\u3002\nmysql> select sum(sal),min(sal),max(sal),avg(sal),count(*) from emp;\r\n+----------+----------+----------+-------------+----------+\r\n| sum(sal) | min(sal) | max(sal) | avg(sal)    | count(*) |\r\n+----------+----------+----------+-------------+----------+\r\n| 29025.00 |   800.00 |  5000.00 | 2073.214286 |       14 |\r\n+----------+----------+----------+-------------+----------+<\/code><\/pre>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"_links":{"self":[{"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts\/219"}],"collection":[{"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=219"}],"version-history":[{"count":1,"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts\/219\/revisions"}],"predecessor-version":[{"id":220,"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts\/219\/revisions\/220"}],"wp:attachment":[{"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=219"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=219"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=219"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}