{"id":214,"date":"2021-08-10T23:17:37","date_gmt":"2021-08-10T15:17:37","guid":{"rendered":"https:\/\/9iwd.top\/?p=214"},"modified":"2021-08-11T10:47:12","modified_gmt":"2021-08-11T02:47:12","slug":"no7-mysql-%e5%b8%b8%e8%a7%81%e5%8d%95%e8%a1%8c%e5%a4%84%e7%90%86%e5%87%bd%e6%95%b0","status":"publish","type":"post","link":"http:\/\/9iwd.top\/?p=214","title":{"rendered":"No7 mysql \u6570\u636e\u5904\u7406\u51fd\u6570"},"content":{"rendered":"\n<pre class=\"wp-block-code\"><code>\u8f6c\u6362\u5c0f\u5199 : lower()\r\n\u8f6c\u6362\u5927\u5199 : upper()\r\n\u53d6\u5b50\u4e32 : substr()\r\n\u5b57\u7b26\u4e32\u62fc\u63a5 : concat()\r\n\u53d6\u957f\u5ea6 : length()\r\n\u53bb\u7a7a\u683c : trim()\r\n\u56db\u820d\u4e94\u5165 : round()\r\n\u751f\u6210\u968f\u673a\u6570 : rand()\r\nnull\u8f6c\u6362 : ifnull()<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u6574\u4e2a\u8868\u4fe1\u606f\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+-------+--------+-----------+------+------------+---------+---------+--------+\n\nmysql> select * from t_student;\r\n+----+-----------+\r\n| ID | name      |\r\n+----+-----------+\r\n|  1 | zhangsan  |\r\n|  2 | lisi      |\r\n|  3 | wangwu    |\r\n|  4 | jack_son  |\r\n+----+-----------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u8f6c\u6362\u5c0f\u5199 : lower()\r\nmysql> select lower(ename) as ename from emp;\r\n+--------+\r\n| ename  |\r\n+--------+\r\n| smith  |\r\n| allen  |\r\n| ward   |\r\n| jones  |\r\n| martin |\r\n| blake  |\r\n| clark  |\r\n| scott  |\r\n| king   |\r\n| turner |\r\n| adams  |\r\n| james  |\r\n| ford   |\r\n| miller |\r\n+--------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u8f6c\u6362\u5927\u5199 : upper()\r\nmysql> select upper(name) as name from t_student;\r\n+-----------+\r\n| name      |\r\n+-----------+\r\n| ZHANGSAN  |\r\n| LISI      |\r\n| WANGWU    |\r\n| JACK_SON  |\r\n+-----------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u53d6\u5b50\u4e32 : substr()\r\n\/\/substr \u53d6\u5b50\u4e32\uff08substr( \u88ab\u622a\u53d6\u7684\u5b57\u7b26\u4e32, \u8d77\u59cb\u4e0b\u6807,\u622a\u53d6\u7684\u957f\u5ea6)\uff09\n\/\/\u6ce8\u610f\uff1a\u8d77\u59cb\u4e0b\u6807\u4ece1\u5f00\u59cb\uff0c\u6ca1\u67090\nmysql> select substr(ename, 1, 1) as ename from emp;\r\n+-------+\r\n| ename |\r\n+-------+\r\n| S     |\r\n| A     |\r\n| W     |\r\n| J     |\r\n| M     |\r\n| B     |\r\n| C     |\r\n| S     |\r\n| K     |\r\n| T     |\r\n| A     |\r\n| J     |\r\n| F     |\r\n| M     |\r\n+-------+\n\n\/\/\u627e\u51fa\u5458\u5de5\u540d\u5b57\u7b2c\u4e00\u4e2a\u5b57\u6bcd\u662fA\u7684\u5458\u5de5\u4fe1\u606f\uff1f\n\/\/\u7b2c\u4e00\u79cd\u65b9\u5f0f\uff1a\u6a21\u7cca\u67e5\u8be2\nmysql> select ename from emp where ename like 'A%';\r\n+-------+\r\n| ename |\r\n+-------+\r\n| ALLEN |\r\n| ADAMS |\r\n+-------+\n\n\/\/\u7b2c\u4e8c\u79cd\u65b9\u5f0f\uff1asubstr\u51fd\u6570\nmysql> select ename from emp where substr(ename,1,1) = 'A';\r\n+-------+\r\n| ename |\r\n+-------+\r\n| ALLEN |\r\n| ADAMS |\r\n+-------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u5b57\u7b26\u4e32\u62fc\u63a5 : concat()\r\nmysql> select concat(empno,ename) from emp;\r\n+---------------------+\r\n| concat(empno,ename) |\r\n+---------------------+\r\n| 7369SMITH           |\r\n| 7499ALLEN           |\r\n| 7521WARD            |\r\n| 7566JONES           |\r\n| 7654MARTIN          |\r\n| 7698BLAKE           |\r\n| 7782CLARK           |\r\n| 7788SCOTT           |\r\n| 7839KING            |\r\n| 7844TURNER          |\r\n| 7876ADAMS           |\r\n| 7900JAMES           |\r\n| 7902FORD            |\r\n| 7934MILLER          |\r\n+---------------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u53d6\u957f\u5ea6 : length()\r\nmysql> select length(ename) enamelength from emp;\r\n+-------------+\r\n| enamelength |\r\n+-------------+\r\n|           5 |\r\n|           5 |\r\n|           4 |\r\n|           5 |\r\n|           6 |\r\n|           5 |\r\n|           5 |\r\n|           5 |\r\n|           4 |\r\n|           6 |\r\n|           5 |\r\n|           5 |\r\n|           4 |\r\n|           6 |\r\n+-------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u591a\u51fd\u6570\u5e94\u7528:\u67e5\u627e\u8fd4\u56de\u9996\u5b57\u6bcd\u5927\u5199\n\/\/1.\u4f7f\u7528 substr \u53d6\u51fa name \u7b2c\u4e00\u4e2a\u5b50\u4e32;\n\/\/2.\u4f7f\u7528 length \u53d6\u51fa name \u603b\u957f\u5ea6-1(\u5df2\u53d6),\u518d\u4f7f\u7528 substr \u53d6\u51fa name \u5269\u4f59\u5b57\u7b26\u4e32\n\/\/3.\u4f7f\u7528 concat \u5c06\u524d\u540e\u5b57\u7b26\u4e32\u62fc\u63a5\u5728\u4e00\u8d77.\n\nmysql> select concat(upper(substr(name,1,1)),substr(name,2,length(name) - 1)) as result from t_student;\r\n+-----------+\r\n| result    |\r\n+-----------+\r\n| Zhangsan  |\r\n| Lisi      |\r\n| Wangwu    |\r\n| Jack_son  |\r\n+-----------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u53bb\u7a7a\u683c : trim()\r\n\/\/\u76f4\u63a5\u67e5\u8be2,\u8fd4\u56de\u8bb0\u5f55\u7a7a\nmysql> select * from emp where ENAME = '  KING';\r\nEmpty set (0.00 sec)\n\nmysql> select * from emp where ename = trim('   KING');\r\n+-------+-------+-----------+------+------------+---------+------+--------+\r\n| EMPNO | ENAME | JOB       | MGR  | HIREDATE   | SAL     | COMM | DEPTNO |\r\n+-------+-------+-----------+------+------------+---------+------+--------+\r\n|  7839 | KING  | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL |     10 |\r\n+-------+-------+-----------+------+------------+---------+------+--------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u56db\u820d\u4e94\u5165 : round()\r\n\/\/round(\u8981\u820d\u5165\u7684\u5b57\u6bb5,\u89c4\u5b9a\u8981\u8fd4\u56de\u7684\u5c0f\u6570\u4f4d\u6570)\n\nmysql> select round(1236.567, 2) as result from emp;\r\n+---------+\r\n| result  |\r\n+---------+\r\n| 1236.57 |\r\n| 1236.57 |\r\n| 1236.57 |\r\n| 1236.57 |\r\n+---------+\n\n\/\/round \u7b2c\u4e8c\u53c2\u6570\u4e3a\u8d1f\u6570,\u5219\u4ece\u6574\u6570\u5f00\u59cb\u56db\u820d\u4e94\u5165\nmysql> select round(1236.567, -1) as result from emp;\r\n+--------+\r\n| result |\r\n+--------+\r\n|   1240 |\r\n|   1240 |\r\n|   1240 |\r\n|   1240 |\r\n+--------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u751f\u6210\u968f\u673a\u6570 : rand()\r\n\/\/\u8fd4\u56de0~1\u4e4b\u95f4\u7684\u968f\u673a\u6570\nmysql> select RAND();\r\n+--------------------+\r\n| RAND()             |\r\n+--------------------+\r\n| 0.6724663625214867 |\r\n+--------------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u5b9e\u4f8b:\u53d6\u968f\u673a\u6574\u6570\nmysql> select round(rand()*100,0);\r\n+---------------------+\r\n| round(rand()*100,0) |\r\n+---------------------+\r\n|                  98 |\r\n+---------------------+<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/null\u8f6c\u6362 : ifnull()\r\n\/\/ifnull\u662f\u7a7a\u5904\u7406\u51fd\u6570\u3002\u4e13\u95e8\u5904\u7406\u7a7a\u7684\u3002\r\n\/\/\u5728\u6240\u6709\u6570\u636e\u5e93\u5f53\u4e2d\uff0c\u53ea\u8981\u6709NULL\u53c2\u4e0e\u7684\u6570\u5b66\u8fd0\u7b97\uff0c\u6700\u7ec8\u7ed3\u679c\u5c31\u662fNULL\u3002\n\/\/\u8ba1\u7b97\u6bcf\u4e2a\u5458\u5de5\u7684\u5e74\u85aa\uff1f\r\u5e74\u85aa = (\u6708\u85aa + \u6708\u8865\u52a9) * 12\nmysql> select ename, (sal + comm) * 12 as yearsal from emp;\r\n+--------+----------+\r\n| ename  | yearsal  |\r\n+--------+----------+\r\n| SMITH  |     NULL |\r\n| ALLEN  | 22800.00 |\r\n| WARD   | 21000.00 |\r\n| JONES  |     NULL |\r\n| MARTIN | 31800.00 |\r\n| BLAKE  |     NULL |\r\n| CLARK  |     NULL |\r\n| SCOTT  |     NULL |\r\n| KING   |     NULL |\r\n| TURNER | 18000.00 |\r\n| ADAMS  |     NULL |\r\n| JAMES  |     NULL |\r\n| FORD   |     NULL |\r\n| MILLER |     NULL |\r\n+--------+----------+\n\n\/*\n\u6ce8\u610f\uff1aNULL\u53ea\u8981\u53c2\u4e0e\u8fd0\u7b97\uff0c\u6700\u7ec8\u7ed3\u679c\u4e00\u5b9a\u662fNULL\u3002\u4e3a\u4e86\u907f\u514d\u8fd9\u4e2a\u73b0\u8c61\uff0c\u9700\u8981\u4f7f\u7528ifnull\u51fd\u6570\u3002\r\nifnull\u51fd\u6570\u7528\u6cd5\uff1aifnull(\u6570\u636e, \u88ab\u5f53\u505a\u54ea\u4e2a\u503c)\r\n\u5982\u679c\u201c\u6570\u636e\u201d\u4e3aNULL\u7684\u65f6\u5019\uff0c\u628a\u8fd9\u4e2a\u6570\u636e\u7ed3\u6784\u5f53\u505a\u54ea\u4e2a\u503c\u3002\r\n\t\t\t\r\n\u8865\u52a9\u4e3aNULL\u7684\u65f6\u5019\uff0c\u5c06\u8865\u52a9\u5f53\u505a0\n*\/\nmysql> select ename, (sal + ifnull(comm, 0)) * 12 as yearsal from emp;\r\n+--------+----------+\r\n| ename  | yearsal  |\r\n+--------+----------+\r\n| SMITH  |  9600.00 |\r\n| ALLEN  | 22800.00 |\r\n| WARD   | 21000.00 |\r\n| JONES  | 35700.00 |\r\n| MARTIN | 31800.00 |\r\n| BLAKE  | 34200.00 |\r\n| CLARK  | 29400.00 |\r\n| SCOTT  | 36000.00 |\r\n| KING   | 60000.00 |\r\n| TURNER | 18000.00 |\r\n| ADAMS  | 13200.00 |\r\n| JAMES  | 11400.00 |\r\n| FORD   | 36000.00 |\r\n| MILLER | 15600.00 |\r\n+--------+----------+<\/code><\/pre>\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\/214"}],"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=214"}],"version-history":[{"count":4,"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts\/214\/revisions"}],"predecessor-version":[{"id":218,"href":"http:\/\/9iwd.top\/index.php?rest_route=\/wp\/v2\/posts\/214\/revisions\/218"}],"wp:attachment":[{"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=214"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=214"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/9iwd.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=214"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}