{"id":2349,"date":"2020-10-12T13:48:44","date_gmt":"2020-10-12T05:48:44","guid":{"rendered":"http:\/\/admin.evshou.com\/?p=2349"},"modified":"2020-10-15T15:42:55","modified_gmt":"2020-10-15T07:42:55","slug":"2020javaweb%e6%95%99%e7%a8%8b%e4%b9%8bdql%e6%95%b0%e6%8d%ae%e6%9f%a5%e8%af%a2","status":"publish","type":"post","link":"https:\/\/www.9713job.com\/?p=2349","title":{"rendered":"2020Javaweb\u6559\u7a0b\u4e4bDQL\u6570\u636e\u67e5\u8be2"},"content":{"rendered":"

2020Javaweb\u6559\u7a0b\u4e4bDQL\u6570\u636e\u67e5\u8be2<\/h3>\n

DQL\u6570\u636e\u67e5\u8be2<\/h4>\n

\u6570\u636e\u5e93\u6267\u884cDQL\u8bed\u53e5\u4e0d\u4f1a\u5bf9\u6570\u636e\u8fdb\u884c\u6539\u53d8\uff0c\u800c\u662f\u8ba9\u6570\u636e\u5e93\u53d1\u9001\u7ed3\u679c\u96c6\u7ed9\u5ba2\u6237\u7aef\u3002<\/p>\n

\u67e5\u8be2\u8fd4\u56de\u7684\u7ed3\u679c\u96c6\u662f\u4e00\u5f20\u865a\u62df\u8868\u3002<\/p>\n

\u67e5\u8be2\u5173\u952e\u5b57\uff1aSELECT<\/span><\/strong><\/p>\n

\u8bed\u6cd5\uff1a SELECT \u5217\u540d FROM \u8868\u540d \u3010WHERE –> GROUP BY–>HAVING–> ORDER BY–>LIMIT\u3011<\/p>\n

SELECT selection_list \/*\u8981\u67e5\u8be2\u7684\u5217\u540d\u79f0*\/<\/p>\n

FROM table_list \/*\u8981\u67e5\u8be2\u7684\u8868\u540d\u79f0*\/<\/p>\n

WHERE condition \/*\u884c\u6761\u4ef6*\/<\/p>\n

GROUP BY grouping_columns \/*\u5bf9\u7ed3\u679c\u5206\u7ec4*\/<\/p>\n

HAVING condition \/*\u5206\u7ec4\u540e\u7684\u884c\u6761\u4ef6*\/<\/p>\n

ORDER BY sorting_columns \/*\u5bf9\u7ed3\u679c\u6392\u5e8f*\/<\/p>\n

LIMIT offset_start, row_count \/*\u7ed3\u679c\u9650\u5b9a*\/<\/p>\n

\u793a\u4f8b\u64cd\u4f5c\uff1a<\/span><\/strong><\/p>\n

1>\u521b\u5efa\u5b66\u751f\u8868\u5e76\u6dfb\u52a0\u6570\u636e#\u521b\u5efa\u8868stu
\nCREATE TABLE stu (
\nsid CHAR(6),
\nsname VARCHAR(50),
\nage INT,
\ngender VARCHAR(50)
\n);
\n#\u6dfb\u52a0\u6570\u636e
\nINSERT INTO stu VALUES(‘S_1001’, ‘liuYi’, 35, ‘male’);
\nINSERT INTO stu VALUES(‘S_1002’, ‘chenEr’, 15, ‘female’);
\nINSERT INTO stu VALUES(‘S_1003’, ‘zhangSan’, 95, ‘male’);
\nINSERT INTO stu VALUES(‘S_1004’, ‘liSi’, 65, ‘female’);
\nINSERT INTO stu VALUES(‘S_1005’, ‘wangWu’, 55, ‘male’);<\/p>\n

\u521b\u5efa\u96c7\u5458\u8868\u5e76\u6dfb\u52a0\u6570\u636e<\/p>\n

#\u521b\u5efa\u96c7\u5458\u8868
\nCREATE TABLE emp(
\nempno INT,
\nename VARCHAR(50),
\njob VARCHAR(50),
\nmgr INT,
\nhiredate DATE,
\nsal DECIMAL(7,2),
\ncomm decimal(7,2),
\ndeptno INT
\n);
\n#\u6dfb\u52a0\u6570\u636e
\nINSERT INTO emp values(7369,’SMITH’,’CLERK’,7902,’1980-12-17′,800,NULL,20);
\nINSERT INTO emp values(7499,’ALLEN’,’SALESMAN’,7698,’1981-02-20′,1600,300,30);
\nINSERT INTO emp values(7521,’WARD’,’SALESMAN’,7698,’1981-02-22′,1250,500,30);<\/p>\n

\u521b\u5efa\u90e8\u95e8\u8868\u5e76\u6dfb\u52a0\u6570\u636e<\/p>\n

#\u521b\u5efa\u90e8\u95e8\u8868
\nCREATE TABLE dept(
\ndeptno INT,
\ndname varchar(14),
\nloc varchar(13)
\n)CHARSET=utf8;
\n#\u6dfb\u52a0\u6570\u636e
\nINSERT INTO dept values(10, ‘\u8d22\u52a1\u90e8’, ‘beijing’);
\nINSERT INTO dept values(20, ‘java\u5f00\u53d1\u90e8’, ‘tianjin’);
\nINSERT INTO dept values(30, ‘\u6d4b\u8bd5\u90e8’, ‘shanghai’);
\nINSERT INTO dept values(40, ‘\u9500\u552e\u90e8’, ‘shenzheng’);<\/p>\n

3\u67e5\u8be2<\/span><\/strong><\/p>\n

3.1 \u7b80\u5355\u67e5\u8be2<\/p>\n

\u67e5\u8be2\u6240\u6709\u5217 *\u8868\u793a\u6240\u6709\u5217<\/p>\n

SELECT * FROM stu;<\/p>\n

\u67e5\u8be2\u6307\u5b9a\u5217<\/p>\n

SELECT sid, sname, age FROM stu;
\n3.2 \u6761\u4ef6\u67e5\u8be2<\/p>\n

\u6761\u4ef6\u67e5\u8be2\u5c31\u662f\u5728\u67e5\u8be2\u65f6\u7ed9\u51faWHERE\u5b50\u53e5\uff0c\u5728WHERE\u5b50\u53e5\u4e2d\u53ef\u4ee5\u4f7f\u7528\u5982\u4e0b\u8fd0\u7b97\u7b26\u53ca\u5173\u952e\u5b57\uff1a<\/p>\n

4.\u8fd0\u7b97\u7b26<\/span><\/strong><\/p>\n

\u6bd4\u8f83\u8fd0\u7b97\u7b26<\/p>\n

l =\u3001!=\u3001<>\u3001<\u3001<=\u3001>\u3001>=\uff1b<\/p>\n

l BETWEEN\u2026AND\uff1b<\/p>\n

l IN(set)\uff1b<\/p>\n

l IS NULL\uff1b<\/p>\n

\u5173\u7cfb\u8fd0\u7b97\u7b26<\/p>\n

l AND\uff1b &&<\/p>\n

l OR\uff1b ||<\/p>\n

l NOT\uff1b !<\/p>\n

\u7b97\u672f\u8fd0\u7b97\u7b26:<\/p>\n

+ – * \/ %<\/p>\n

(1)\u67e5\u8be2\u6027\u522b\u4e3a\u5973\uff0c\u5e76\u4e14\u5e74\u9f84\u5c0f\u4e8e50\u7684\u8bb0\u5f55<\/p>\n

SELECT * FROM stu WHERE gender=’female’ AND age<50;<\/p>\n

(2)\u67e5\u8be2\u5b66\u53f7\u4e3aS_1001\uff0c\u6216\u8005\u59d3\u540d\u4e3aliSi\u7684\u8bb0\u5f55<\/p>\n

SELECT * FROM stu WHERE sid =’S_1001′ OR sname=’liSi’;<\/p>\n

(3)\u67e5\u8be2\u5b66\u53f7\u4e3aS _ 1001 \uff0cS _ 1002\uff0cS _ 1003\u7684\u8bb0\u5f55<\/p>\n

SELECT * FROM stu
\nWHERE sid IN (‘S_1001′,’S_1002′,’S_1003′);
\n\u7b49\u540c\u4e8e
\nSELECT * FROM stu
\nWHERE sid=’S_1001′ or sid=’S_1002′ or sid=’S_1003’;<\/p>\n

(4)\u67e5\u8be2\u5b66\u53f7\u4e0d\u662fS_1001\uff0cS_1002\uff0cS_1003\u7684\u8bb0\u5f55<\/p>\n

SELECT * FROM tab_student
\nWHERE sid NOT IN(‘S1001′,’S1002′,’S_1003′);<\/p>\n

(5)\u67e5\u8be2\u5e74\u9f84\u4e3anull\u7684\u8bb0\u5f55<\/p>\n

SELECT * FROM stu WHERE age IS NULL;<\/p>\n

(6)\u67e5\u8be2\u5e74\u9f84\u572820\u523040\u4e4b\u95f4\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE age>=20 AND age<=40;<\/p>\n

\u6216\u8005<\/p>\n

SELECT *
\nFROM stu
\nWHERE age BETWEEN 20 AND 40;<\/p>\n

(7)\u3000\u67e5\u8be2\u6027\u522b\u975e\u7537\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE gender!=’male’;<\/p>\n

\u6216\u8005<\/p>\n

SELECT *
\nFROM stu
\nWHERE gender<>’male’;<\/p>\n

\u6216\u8005<\/p>\n

SELECT *
\nFROM stu
\nWHERE NOT gender=’male’;<\/p>\n

(8) \u67e5\u8be2\u59d3\u540d\u4e0d\u4e3anull\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE NOT sname IS NULL;<\/p>\n

\u6216\u8005<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname IS NOT NULL;<\/p>\n

3.3 \u6a21\u7cca\u67e5\u8be2<\/span><\/strong><\/p>\n

\u5f53\u60f3\u67e5\u8be2\u59d3\u540d\u4e2d\u5305\u542ba\u5b57\u6bcd\u7684\u5b66\u751f\u65f6\u5c31\u9700\u8981\u4f7f\u7528\u6a21\u7cca\u67e5\u8be2\u4e86\u3002\u6a21\u7cca\u67e5\u8be2\u9700\u8981\u4f7f\u7528\u5173\u952e\u5b57LIKE\u3002<\/p>\n

\u901a\u914d\u7b26:<\/p>\n

_ \u4efb\u610f\u4e00\u4e2a\u5b57\u7b26<\/p>\n

%\uff1a\u4efb\u610f0~n\u4e2a\u5b57\u7b26<\/p>\n

‘\u5f20%’ —\u300b\u5f20\u4e09\u4e30 \u5f20\u4e09 \u5f20\u65e0\u5fcc<\/p>\n

‘\u674e_’ —>\u674e\u56db \u674e\u9035 \u674e\u521a<\/p>\n

(1)\u67e5\u8be2\u59d3\u540d\u75313\u4e2a\u5b57\u7b26\u6784\u6210\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname LIKE ‘___’;<\/p>\n

\u6a21\u7cca\u67e5\u8be2\u5fc5\u987b\u4f7f\u7528LIKE\u5173\u952e\u5b57\u3002\u5176\u4e2d \u201c\u201d\u5339\u914d\u4efb\u610f\u4e00\u4e2a\u5b57\u6bcd\uff0c5\u4e2a\u201c\u201d\u8868\u793a5\u4e2a\u4efb\u610f\u5b57\u6bcd\u3002<\/p>\n

(2)\u67e5\u8be2\u59d3\u540d\u75315\u4e2a\u5b57\u7b26\u6784\u6210\uff0c\u5e76\u4e14\u7b2c5\u4e2a\u5b57\u7b26\u4e3a\u201ci\u201d\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname LIKE ‘____i’;<\/p>\n

(3)\u67e5\u8be2\u59d3\u540d\u4ee5\u201cz\u201d\u5f00\u5934\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname LIKE ‘z%’;<\/p>\n

\u5176\u4e2d\u201c%\u201d\u5339\u914d0~n\u4e2a\u4efb\u4f55\u5b57\u7b26\u3002<\/p>\n

(4)\u67e5\u8be2\u59d3\u540d\u4e2d\u7b2c2\u4e2a\u5b57\u7b26\u4e3a\u201ci\u201d\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname LIKE ‘_i%’;<\/p>\n

(5)\u67e5\u8be2\u59d3\u540d\u4e2d\u5305\u542b\u201ca\u201d\u5b57\u7b26\u7684\u5b66\u751f\u8bb0\u5f55<\/p>\n

SELECT *
\nFROM stu
\nWHERE sname LIKE ‘%a%’;<\/p>\n

3.4 \u5b57\u6bb5\u63a7\u5236\u67e5\u8be2<\/span><\/strong><\/p>\n

(1)\u53bb\u9664\u91cd\u590d\u8bb0\u5f55<\/p>\n

\u53bb\u9664\u91cd\u590d\u8bb0\u5f55\uff08\u4e24\u884c\u6216\u4e24\u884c\u4ee5\u4e0a\u8bb0\u5f55\u4e2d\u5217\u7684\u6570\u636e\u90fd\u76f8\u540c\uff09\uff0c\u4f8b\u5982emp\u8868\u4e2dsal\u5b57\u6bb5\u5c31\u5b58\u5728\u76f8\u540c\u7684\u8bb0\u5f55\u3002\u5f53\u53ea\u67e5\u8be2emp\u8868\u7684sal\u5b57\u6bb5\u65f6\uff0c\u90a3\u4e48\u4f1a\u51fa\u73b0\u91cd\u590d\u8bb0\u5f55\uff0c\u90a3\u4e48\u60f3\u53bb\u9664\u91cd\u590d\u8bb0\u5f55\uff0c\u9700\u8981\u4f7f\u7528DISTINCT\uff1a<\/p>\n

SELECT DISTINCT sal FROM emp;
\nSELECT DISTINCT sal,comm FROM emp;<\/p>\n

(2)\u67e5\u770b\u96c7\u5458\u7684\u6708\u85aa\u4e0e\u4f63\u91d1\u4e4b\u548c<\/p>\n

\u56e0\u4e3asal\u548ccomm\u4e24\u5217\u7684\u7c7b\u578b\u90fd\u662f\u6570\u503c\u7c7b\u578b\uff0c\u6240\u4ee5\u53ef\u4ee5\u505a\u52a0\u8fd0\u7b97\u3002\u5982\u679csal\u6216comm\u4e2d\u6709\u4e00\u4e2a\u5b57\u6bb5\u4e0d\u662f\u6570\u503c\u7c7b\u578b\uff0c\u90a3\u4e48\u4f1a\u51fa\u9519\u3002<\/p>\n

SELECT *,sal+comm FROM emp;
\n\u200b
\n\u5b57\u7b26\u4e32\u7684\u5408\u5e76\u4e0d\u80fd\u4f7f\u7528+ ,\u4f7f\u7528concat(ename,’____’,job);
\nselect *,concat(ename,’______’,job) from emp;<\/p>\n

comm\u5217\u6709\u5f88\u591a\u8bb0\u5f55\u7684\u503c\u4e3aNULL\uff0c\u56e0\u4e3a\u4efb\u4f55\u4e1c\u897f\u4e0eNULL\u76f8\u52a0\u7ed3\u679c\u8fd8\u662fNULL\uff0c\u6240\u4ee5\u7ed3\u7b97\u7ed3\u679c\u53ef\u80fd\u4f1a\u51fa\u73b0NULL\u3002\u4e0b\u9762\u4f7f\u7528\u4e86\u628aNULL\u8f6c\u6362\u6210\u6570\u503c0\u7684\u51fd\u6570IFNULL\uff1a<\/p>\n

SELECT *,sal+IFNULL(comm,0) FROMemp;<\/p>\n

(3)\u7ed9\u5217\u540d\u6dfb\u52a0\u522b\u540d<\/p>\n

\u5728\u4e0a\u9762\u67e5\u8be2\u4e2d\u51fa\u73b0\u5217\u540d\u4e3asal+IFNULL(comm,0)\uff0c\u8fd9\u5f88\u4e0d\u7f8e\u89c2\uff0c\u73b0\u5728\u6211\u4eec\u7ed9\u8fd9\u4e00\u5217\u7ed9\u51fa\u4e00\u4e2a\u522b\u540d\uff0c\u4e3atotal\uff1a<\/p>\n

SELECT *, sal+IFNULL(comm,0) AS total FROM emp;<\/p>\n

\u7ed9\u5217\u8d77\u522b\u540d\u65f6\uff0c\u662f\u53ef\u4ee5\u7701\u7565AS\u5173\u952e\u5b57\u7684\uff1a<\/p>\n

SELECT *,sal+IFNULL(comm,0) total FROM emp;<\/p>\n

3.5 \u6392\u5e8f<\/span><\/strong><\/p>\n

(1)\u3000\u67e5\u8be2\u6240\u6709\u5b66\u751f\u8bb0\u5f55\uff0c\u6309\u5e74\u9f84\u5347\u5e8f\u6392\u5e8f<\/p>\n

SELECT *
\nFROM stu
\nORDER BY age ASC;<\/p>\n

\u6216\u8005<\/p>\n

SELECT *
\nFROM stu
\nORDER BY age;<\/p>\n

(2)\u3000\u67e5\u8be2\u6240\u6709\u5b66\u751f\u8bb0\u5f55\uff0c\u6309\u5e74\u9f84\u964d\u5e8f\u6392\u5e8f<\/p>\n

SELECT *
\nFROM stu
\nORDER BY age DESC;<\/p>\n

(3)\u3000\u67e5\u8be2\u6240\u6709\u96c7\u5458\uff0c\u6309\u6708\u85aa\u964d\u5e8f\u6392\u5e8f\uff0c\u5982\u679c\u6708\u85aa\u76f8\u540c\u65f6\uff0c\u6309\u7f16\u53f7\u5347\u5e8f\u6392\u5e8f<\/p>\n

SELECT * FROM emp
\nORDER BY sal DESC,empno ASC;<\/p>\n

3.6 \u805a\u5408\u51fd\u6570<\/span><\/strong><\/p>\n

\u805a\u5408\u51fd\u6570\u662f\u7528\u6765\u505a\u7eb5\u5411\u8fd0\u7b97\u7684\u51fd\u6570\uff1a<\/p>\n

l COUNT()\uff1a\u7edf\u8ba1\u6307\u5b9a\u5217\u4e0d\u4e3aNULL\u7684\u8bb0\u5f55\u884c\u6570\uff1b<\/p>\n

l MAX()\uff1a\u8ba1\u7b97\u6307\u5b9a\u5217\u7684\u6700\u5927\u503c\uff0c\u5982\u679c\u6307\u5b9a\u5217\u662f\u5b57\u7b26\u4e32\u7c7b\u578b\uff0c\u90a3\u4e48\u4f7f\u7528\u5b57\u7b26\u4e32\u6392\u5e8f\u8fd0\u7b97\uff1b<\/p>\n

l MIN()\uff1a\u8ba1\u7b97\u6307\u5b9a\u5217\u7684\u6700\u5c0f\u503c\uff0c\u5982\u679c\u6307\u5b9a\u5217\u662f\u5b57\u7b26\u4e32\u7c7b\u578b\uff0c\u90a3\u4e48\u4f7f\u7528\u5b57\u7b26\u4e32\u6392\u5e8f\u8fd0\u7b97\uff1b<\/p>\n

l SUM()\uff1a\u8ba1\u7b97\u6307\u5b9a\u5217\u7684\u6570\u503c\u548c\uff0c\u5982\u679c\u6307\u5b9a\u5217\u7c7b\u578b\u4e0d\u662f\u6570\u503c\u7c7b\u578b\uff0c\u90a3\u4e48\u8ba1\u7b97\u7ed3\u679c\u4e3a0\uff1b<\/p>\n

l AVG()\uff1a\u8ba1\u7b97\u6307\u5b9a\u5217\u7684\u5e73\u5747\u503c\uff0c\u5982\u679c\u6307\u5b9a\u5217\u7c7b\u578b\u4e0d\u662f\u6570\u503c\u7c7b\u578b\uff0c\u90a3\u4e48\u8ba1\u7b97\u7ed3\u679c\u4e3a0\uff1b<\/p>\n

(1)\u3000COUNT<\/span><\/strong><\/p>\n

\u5f53\u9700\u8981\u7eb5\u5411\u7edf\u8ba1\u65f6\u53ef\u4ee5\u4f7f\u7528COUNT()\u3002<\/p>\n

l \u67e5\u8be2emp\u8868\u4e2d\u8bb0\u5f55\u6570\uff1a<\/p>\n

SELECT COUNT(*) AS \u2018cnt\u2019 FROM emp;<\/p>\n

l \u67e5\u8be2emp\u8868\u4e2d\u6709\u4f63\u91d1\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT COUNT(comm) \u2018cnt\u2019 FROM emp;<\/p>\n

\u6ce8\u610f\uff0c\u56e0\u4e3acount()\u51fd\u6570\u4e2d\u7ed9\u51fa\u7684\u662fcomm\u5217\uff0c\u90a3\u4e48\u53ea\u7edf\u8ba1comm\u5217\u975eNULL\u7684\u884c\u6570\u3002<\/p>\n

l \u67e5\u8be2emp\u8868\u4e2d\u6708\u85aa\u5927\u4e8e2500\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT COUNT(*) FROM emp
\nWHERE sal > 2500;<\/p>\n

l \u7edf\u8ba1\u6708\u85aa\u4e0e\u4f63\u91d1\u4e4b\u548c\u5927\u4e8e2500\u5143\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT COUNT(*) AS cnt FROM emp WHERE sal+IFNULL(comm,0) > 2500;<\/p>\n

l \u67e5\u8be2\u6709\u4f63\u91d1\u7684\u4eba\u6570\uff0c\u4ee5\u53ca\u6709\u9886\u5bfc\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT COUNT(comm), COUNT(mgr)FROM emp;<\/p>\n

(2)\u3000SUM\u548cAVG<\/span><\/strong><\/p>\n

\u5f53\u9700\u8981\u7eb5\u5411\u6c42\u548c\u65f6\u4f7f\u7528sum()\u51fd\u6570\u3002<\/p>\n

l \u67e5\u8be2\u6240\u6709\u96c7\u5458\u6708\u85aa\u548c\uff1a<\/p>\n

SELECT SUM(sal) FROM emp;<\/p>\n

l \u67e5\u8be2\u6240\u6709\u96c7\u5458\u6708\u85aa\u548c\uff0c\u4ee5\u53ca\u6240\u6709\u96c7\u5458\u4f63\u91d1\u548c\uff1a<\/p>\n

SELECT SUM(sal), SUM(comm) FROMemp;<\/p>\n

l \u67e5\u8be2\u6240\u6709\u96c7\u5458\u6708\u85aa+\u4f63\u91d1\u548c\uff1a<\/p>\n

SELECT SUM(sal+IFNULL(comm,0))FROM emp;<\/p>\n

l \u7edf\u8ba1\u6240\u6709\u5458\u5de5\u5e73\u5747\u5de5\u8d44\uff1a<\/p>\n

SELECT AVG(sal) FROM emp;<\/p>\n

(3)\u3000MAX\u548cMIN<\/span><\/strong><\/p>\n

l \u67e5\u8be2\u6700\u9ad8\u5de5\u8d44\u548c\u6700\u4f4e\u5de5\u8d44\uff1a<\/p>\n

SELECT MAX(sal), MIN(sal) FROM emp;<\/p>\n

3.7 \u5206\u7ec4\u67e5\u8be2<\/span><\/strong><\/p>\n

\u5f53\u9700\u8981\u5206\u7ec4\u67e5\u8be2\u65f6\u9700\u8981\u4f7f\u7528GROUP BY\u5b50\u53e5\uff0c\u4f8b\u5982\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5de5\u8d44\u548c\uff0c\u8fd9\u8bf4\u660e\u8981\u4f7f\u7528\u90e8\u5206\u6765\u5206\u7ec4\u3002<\/p>\n

\u6ce8\uff1a\u51e1\u662f\u548c\u805a\u5408\u51fd\u6570\u540c\u65f6\u51fa\u73b0\u7684\u5217\u540d\uff0c\u5219\u4e00\u5b9a\u8981\u5199\u5728group by \u4e4b\u540e<\/p>\n

3.7.1 \u5206\u7ec4\u67e5\u8be2<\/p>\n

l \u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u90e8\u95e8\u7f16\u53f7\u548c\u6bcf\u4e2a\u90e8\u95e8\u7684\u5de5\u8d44\u548c\uff1a<\/p>\n

SELECT deptno, SUM(sal)
\nFROM emp
\nGROUP BY deptno;<\/p>\n

l \u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u90e8\u95e8\u7f16\u53f7\u4ee5\u53ca\u6bcf\u4e2a\u90e8\u95e8\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT deptno,COUNT(*)
\nFROM emp
\nGROUP BY deptno;<\/p>\n

l \u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u90e8\u95e8\u7f16\u53f7\u4ee5\u53ca\u6bcf\u4e2a\u90e8\u95e8\u5de5\u8d44\u5927\u4e8e1500\u7684\u4eba\u6570\uff1a<\/p>\n

SELECT deptno,COUNT(*)
\nFROM emp
\nWHERE sal>1500
\nGROUP BY deptno;
\n3.7.2 HAVING\u5b50\u53e5<\/p>\n

l \u67e5\u8be2\u5de5\u8d44\u603b\u548c\u5927\u4e8e9000\u7684\u90e8\u95e8\u7f16\u53f7\u4ee5\u53ca\u5de5\u8d44\u548c\uff1a<\/p>\n

SELECT deptno, SUM(sal)
\nFROM emp
\nGROUP BY deptno
\nHAVING SUM(sal) > 9000;<\/p>\n

\u6ce8\uff1ahaving\u4e0ewhere\u7684\u533a\u522b:<\/span><\/p>\n

1.having\u662f\u5728\u5206\u7ec4\u540e\u5bf9\u6570\u636e\u8fdb\u884c\u8fc7\u6ee4,where\u662f\u5728\u5206\u7ec4\u524d\u5bf9\u6570\u636e\u8fdb\u884c\u8fc7\u6ee4<\/span><\/p>\n

2.having\u540e\u9762\u53ef\u4ee5\u4f7f\u7528\u5206\u7ec4\u51fd\u6570(\u7edf\u8ba1\u51fd\u6570)<\/span><\/p>\n

where\u540e\u9762\u4e0d\u53ef\u4ee5\u4f7f\u7528\u5206\u7ec4\u51fd\u6570\u3002<\/span><\/p>\n

where\u662f\u5bf9\u5206\u7ec4\u524d\u8bb0\u5f55\u7684\u6761\u4ef6\uff0c\u5982\u679c\u67d0\u884c\u8bb0\u5f55\u6ca1\u6709\u6ee1\u8db3WHERE\u5b50\u53e5\u7684\u6761\u4ef6\uff0c\u90a3\u4e48\u8fd9\u884c\u8bb0\u5f55\u4e0d\u4f1a\u53c2\u52a0\u5206\u7ec4\uff1b\u800c having\u662f\u5bf9\u5206\u7ec4\u540e\u6570\u636e\u7684\u7ea6\u675f\u3002<\/span><\/p>\n

3.8 LIMIT\u9650\u5236<\/span><\/strong><\/p>\n

LIMIT\u7528\u6765\u9650\u5b9a\u67e5\u8be2\u7ed3\u679c\u7684\u8d77\u59cb\u884c\uff0c\u4ee5\u53ca\u603b\u884c\u6570\u3002<\/p>\n

1\u67e5\u8be2\u524d5\u884c\u8bb0\u5f55\uff0c\u8d77\u59cb\u884c\u4ece0\u5f00\u59cb<\/p>\n

SELECT * FROM emp LIMIT 0, 5;<\/p>\n

\u6ce8\u610f\uff0c\u8d77\u59cb\u884c\u4ece0\u5f00\u59cb\uff0c\u5373\u7b2c\u4e00\u884c\u5f00\u59cb\uff01<\/p>\n

2\u67e5\u8be210\u884c\u8bb0\u5f55\uff0c\u8d77\u59cb\u884c\u4ece3\u5f00\u59cb<\/p>\n

SELECT* FROM emp LIMIT 3, 10;
\n3.8.1\u5206\u9875\u67e5\u8be2<\/p>\n

\u5982\u679c\u4e00\u9875\u8bb0\u5f55\u4e3a10\u6761\uff0c\u5e0c\u671b\u67e5\u770b\u7b2c3\u9875\u8bb0\u5f55\u5e94\u8be5\u600e\u4e48\u67e5\u5462\uff1f<\/p>\n

l \u7b2c\u4e00\u9875\u8bb0\u5f55\u8d77\u59cb\u884c\u4e3a0\uff0c\u4e00\u5171\u67e5\u8be210\u884c\uff1b<\/p>\n

l \u7b2c\u4e8c\u9875\u8bb0\u5f55\u8d77\u59cb\u884c\u4e3a10\uff0c\u4e00\u5171\u67e5\u8be210\u884c\uff1b<\/p>\n

l \u7b2c\u4e09\u9875\u8bb0\u5f55\u8d77\u59cb\u884c\u4e3a20\uff0c\u4e00\u5171\u67e5\u8be210\u884c\uff1b<\/p>\n

\u603b\u7ed3\u67e5\u8be2<\/p>\n

\u67e5\u8be2\u8bed\u53e5\u4e66\u5199\u987a\u5e8f\uff1aselect \u5217 from \u8868 \u3010where- group by- having- order by-limit\u3011<\/p>\n

\u67e5\u8be2\u8bed\u53e5\u6267\u884c\u987a\u5e8f\uff1afrom \u8868 where -group by -having – select – order by-limit<\/p>\n

\u603b\u7ed3<\/p>\n

1 \u6570\u636e\u5e93\uff1a\u5b58\u50a8\u6570\u636e\u7684\u4ed3\u5e93\u3002<\/p>\n

2 \u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf: MySQL Oracle SQL Server DB2<\/p>\n

3 MySQL\u5b89\u88c5\u3001\u5378\u8f7d<\/p>\n

4 SQL\u8bed\u53e5\uff1a<\/p>\n

DDL \u6570\u636e\u5b9a\u4e49\u8bed\u8a00 \u521b\u5efa\u5e93\uff0c\u521b\u5efa\u8868<\/p>\n

DML\u6570\u636e\u64cd\u505a\u8bed\u8a00 \u6dfb\u52a0 \u5220\u9664 \u66f4\u65b0 insert delete udpate<\/p>\n

DQL \u6570\u636e\u67e5\u8be2\u8bed\u8a00 select<\/p>\n

DCL \u6570\u636e\u63a7\u5236\u8bed\u8a00\uff0c \u7528\u6237\u7684\u521b\u5efa \u6743\u9650\u5206\u914d\u3002<\/p>\n

5 DQL<\/p>\n

\u7b80\u5355\u67e5\u8be2 select \u5217\u540d from \u8868\u540d<\/p>\n

\u6761\u4ef6\u67e5\u8be2 where \u8fd0\u7b97\u7b26 = != <> > >= < <= in between and \u3001 and or not + – * \/ %<\/p>\n

\u6a21\u7cca\u67e5\u8be2 like\u5173\u952e\u5b57 \u901a\u914d\u7b26 _\u8868\u793a\u4e00\u4e2a\u5b57\u7b26 %\u8868\u793a\u4efb\u610f\u591a\u4e2a\u5b57\u7b26<\/p>\n

\u5b57\u6bb5\u63a7\u5236 distinct \u53bb\u91cd \u5408\u5e76 concat \u522b\u540d as<\/p>\n

\u6392\u5e8f order by<\/p>\n

\u805a\u5408\u51fd\u6570 count sum max min avg<\/p>\n

\u5206\u7ec4\u67e5\u8be2 group by \u7b5b\u9009\u8fc7\u6ee4 having<\/p>\n

limit \u9650\u5236\u67e5\u8be2 \u5206\u9875<\/p>\n","protected":false},"excerpt":{"rendered":"

2020Javaweb\u6559\u7a0b\u4e4bDQL\u6570\u636e\u67e5\u8be2 DQL\u6570\u636e\u67e5\u8be2 \u6570\u636e\u5e93\u6267\u884cDQL\u8bed\u53e5\u4e0d\u4f1a\u5bf9\u6570\u636e\u8fdb\u884c\u6539\u53d8\uff0c\u800c\u662f\u8ba9\u6570\u636e […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-2349","post","type-post","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/posts\/2349","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.9713job.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2349"}],"version-history":[{"count":1,"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/posts\/2349\/revisions"}],"predecessor-version":[{"id":2350,"href":"https:\/\/www.9713job.com\/index.php?rest_route=\/wp\/v2\/posts\/2349\/revisions\/2350"}],"wp:attachment":[{"href":"https:\/\/www.9713job.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2349"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.9713job.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2349"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.9713job.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2349"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}