{"id":619,"date":"2024-12-28T21:27:55","date_gmt":"2024-12-28T13:27:55","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=619"},"modified":"2024-12-28T21:27:55","modified_gmt":"2024-12-28T13:27:55","slug":"%e5%ae%9e%e7%94%a8%e7%9a%84sql%e5%ae%9e%e4%be%8b","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2024\/12\/28\/%e5%ae%9e%e7%94%a8%e7%9a%84sql%e5%ae%9e%e4%be%8b\/","title":{"rendered":"\u5b9e\u7528\u7684SQL\u5b9e\u4f8b"},"content":{"rendered":"\n
\n

\u597d\u7684\uff01\u4e3a\u4e86\u5e2e\u52a9\u4f60\u66f4\u597d\u5730\u7406\u89e3\u548c\u638c\u63e1SQL\uff0c\u4ee5\u4e0b\u662f\u51e0\u4e2a\u5b9e\u7528\u7684SQL\u5b9e\u4f8b\uff0c\u6db5\u76d6\u4e86\u57fa\u7840\u67e5\u8be2\u3001\u590d\u6742\u67e5\u8be2\u3001\u7a97\u53e3\u51fd\u6570\u3001\u4e8b\u52a1\u7ba1\u7406\u3001\u6570\u636e\u5e93\u4f18\u5316\u7b49\u5185\u5bb9\u3002<\/p>\n<\/blockquote>\n\n\n\n

1. \u57fa\u672c\u67e5\u8be2\u64cd\u4f5c<\/strong><\/h3>\n\n\n\n

\u67e5\u8be2\u6240\u6709\u8bb0\u5f55<\/h4>\n\n\n\n

\u5047\u8bbe\u6709\u4e00\u4e2a\u8868 students<\/code>\uff0c\u5305\u542b\u5b66\u751f\u4fe1\u606f\uff1a<\/p>\n\n\n\n

id<\/th>name<\/th>age<\/th>grade<\/th><\/tr><\/thead>
1<\/td>Alice<\/td>20<\/td>A<\/td><\/tr>
2<\/td>Bob<\/td>22<\/td>B<\/td><\/tr>
3<\/td>Charlie<\/td>21<\/td>A<\/td><\/tr>
4<\/td>Dave<\/td>23<\/td>C<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

\u67e5\u8be2\u6240\u6709\u5b66\u751f\u7684\u4fe1\u606f\uff1a<\/p>\n\n\n\n

SELECT * FROM students;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u7279\u5b9a\u5217<\/h4>\n\n\n\n
\u67e5\u8be2\u6240\u6709\u5b66\u751f\u7684\u59d3\u540d\u548c\u5e74\u9f84\uff1a<\/p>\n\n\n\n
SELECT name, age FROM students;<\/code><\/pre>\n\n\n\n
\u4f7f\u7528WHERE<\/code>\u6761\u4ef6\u7b5b\u9009<\/h4>\n\n\n\n
\u67e5\u8be2\u6240\u6709\u5e74\u9f84\u5927\u4e8e21\u5c81\u7684\u5b66\u751f\uff1a<\/p>\n\n\n\n
SELECT * FROM students WHERE age > 21;<\/code><\/pre>\n\n\n\n
\u6392\u5e8f\u6570\u636e<\/h4>\n\n\n\n
\u67e5\u8be2\u6240\u6709\u5b66\u751f\u5e76\u6309\u5e74\u9f84\u5347\u5e8f\u6392\u5e8f\uff1a<\/p>\n\n\n\n
SELECT * FROM students ORDER BY age ASC;<\/code><\/pre>\n\n\n\n
\u9650\u5236\u7ed3\u679c<\/h4>\n\n\n\n
\u67e5\u8be2\u524d\u4e24\u540d\u5b66\u751f\u7684\u59d3\u540d\u548c\u5e74\u9f84\uff1a<\/p>\n\n\n\n
SELECT name, age FROM students LIMIT 2;<\/code><\/pre>\n\n\n\n
\n\n\n\n
2. \u805a\u5408\u51fd\u6570\u4e0e\u5206\u7ec4<\/strong><\/h3>\n\n\n\n
\u4f7f\u7528\u805a\u5408\u51fd\u6570<\/h4>\n\n\n\n
\u8ba1\u7b97\u6240\u6709\u5b66\u751f\u7684\u5e73\u5747\u5e74\u9f84\uff1a<\/p>\n\n\n\n
SELECT AVG(age) AS average_age FROM students;<\/code><\/pre>\n\n\n\n
\u4f7f\u7528GROUP BY<\/code>\u5206\u7ec4<\/h4>\n\n\n\n
\u6309\u6210\u7ee9\u5206\u7ec4\uff0c\u7edf\u8ba1\u6bcf\u4e2a\u6210\u7ee9\u7b49\u7ea7\u7684\u4eba\u6570\uff1a<\/p>\n\n\n\n
SELECT grade, COUNT(*) AS student_count FROM students GROUP BY grade;<\/code><\/pre>\n\n\n\n
\u7ed3\u5408HAVING<\/code>\u7b5b\u9009<\/h4>\n\n\n\n
\u67e5\u8be2\u6210\u7ee9\u4e3a”A”\u7684\u5b66\u751f\u5e73\u5747\u5e74\u9f84\u5927\u4e8e21\u5c81\u7684\u4eba\u6570\uff1a<\/p>\n\n\n\n
SELECT grade, AVG(age) AS average_age\nFROM students\nGROUP BY grade\nHAVING grade = 'A' AND AVG(age) > 21;<\/code><\/pre>\n\n\n\n
\n\n\n\n
3. \u8fde\u63a5\u67e5\u8be2\uff08JOIN\uff09<\/strong><\/h3>\n\n\n\n
\u5047\u8bbe\u6709\u4e24\u5f20\u8868\uff1astudents<\/code> \u548c courses<\/code>\uff0c\u5b66\u751f\u9009\u8bfe\u4fe1\u606f\u5982\u4e0b\uff1a<\/p>\n\n\n\n
students<\/code> \u8868\uff1a<\/p>\n\n\n\n
id<\/th>name<\/th><\/tr><\/thead>
1<\/td>Alice<\/td><\/tr>
2<\/td>Bob<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
courses<\/code> \u8868\uff1a<\/p>\n\n\n\n
student_id<\/th>course<\/th><\/tr><\/thead>
1<\/td>Math<\/td><\/tr>
1<\/td>Science<\/td><\/tr>
2<\/td>History<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
INNER JOIN<\/code><\/h4>\n\n\n\n
\u67e5\u8be2\u6bcf\u4e2a\u5b66\u751f\u6240\u9009\u7684\u8bfe\u7a0b\uff1a<\/p>\n\n\n\n
SELECT students.name, courses.course\nFROM students\nINNER JOIN courses ON students.id = courses.student_id;<\/code><\/pre>\n\n\n\n
LEFT JOIN<\/code><\/h4>\n\n\n\n
\u67e5\u8be2\u6bcf\u4e2a\u5b66\u751f\u53ca\u5176\u9009\u7684\u8bfe\u7a0b\uff0c\u5982\u679c\u6ca1\u6709\u9009\u8bfe\u5219\u663e\u793aNULL\uff1a<\/p>\n\n\n\n
SELECT students.name, courses.course\nFROM students\nLEFT JOIN courses ON students.id = courses.student_id;<\/code><\/pre>\n\n\n\n
\n\n\n\n
4. \u7a97\u53e3\u51fd\u6570<\/strong><\/h3>\n\n\n\n
\u5047\u8bbe\u6709\u4e00\u4e2a sales<\/code> \u8868\uff0c\u8bb0\u5f55\u9500\u552e\u6570\u636e\uff1a<\/p>\n\n\n\n
salesperson<\/th>sales_amount<\/th>sale_date<\/th><\/tr><\/thead>
John<\/td>500<\/td>2024-01-01<\/td><\/tr>
Jane<\/td>600<\/td>2024-01-02<\/td><\/tr>
John<\/td>700<\/td>2024-01-03<\/td><\/tr>
Jane<\/td>800<\/td>2024-01-04<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\u4f7f\u7528 ROW_NUMBER()<\/code> \u6392\u540d<\/h4>\n\n\n\n
\u6309\u9500\u552e\u91d1\u989d\u964d\u5e8f\u6392\u540d\uff1a<\/p>\n\n\n\n
SELECT salesperson, sales_amount, ROW_NUMBER() OVER (ORDER BY sales_amount DESC) AS rank\nFROM sales;<\/code><\/pre>\n\n\n\n
\u4f7f\u7528 LEAD()<\/code> \u548c LAG()<\/code> \u6bd4\u8f83\u524d\u540e\u884c\u6570\u636e<\/h4>\n\n\n\n
\u6bd4\u8f83\u6bcf\u4e2a\u9500\u552e\u5458\u5f53\u524d\u548c\u4e0a\u4e00\u5929\u7684\u9500\u552e\u989d\u5dee\uff1a<\/p>\n\n\n\n
SELECT salesperson, sales_amount, LAG(sales_amount) OVER (PARTITION BY salesperson ORDER BY sale_date) AS previous_sales,\n       sales_amount - LAG(sales_amount) OVER (PARTITION BY salesperson ORDER BY sale_date) AS sales_difference\nFROM sales;<\/code><\/pre>\n\n\n\n
\n\n\n\n
5. \u4e8b\u52a1\u7ba1\u7406<\/strong><\/h3>\n\n\n\n
\u5047\u8bbe\u6709\u4e00\u4e2a\u94f6\u884c\u8d26\u6237\u7684 accounts<\/code> \u8868\uff1a<\/p>\n\n\n\n
account_id<\/th>balance<\/th><\/tr><\/thead>
1<\/td>1000<\/td><\/tr>
2<\/td>2000<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\u5f00\u59cb\u4e8b\u52a1<\/h4>\n\n\n\n
START TRANSACTION;\n\nUPDATE accounts SET balance = balance - 100 WHERE account_id = 1;\nUPDATE accounts SET balance = balance + 100 WHERE account_id = 2;\n\nCOMMIT;  -- \u63d0\u4ea4\u4e8b\u52a1<\/code><\/pre>\n\n\n\n
\u5982\u679c\u4e2d\u9014\u51fa\u73b0\u9519\u8bef\uff0c\u53ef\u4ee5\u4f7f\u7528 ROLLBACK<\/code> \u8fdb\u884c\u56de\u6eda\uff1a<\/p>\n\n\n\n
START TRANSACTION;\n\nUPDATE accounts SET balance = balance - 100 WHERE account_id = 1;\nUPDATE accounts SET balance = balance + 100 WHERE account_id = 2;\n\n-- \u5047\u8bbe\u6b64\u65f6\u53d1\u751f\u9519\u8bef\nROLLBACK;  -- \u56de\u6eda\u4e8b\u52a1<\/code><\/pre>\n\n\n\n
\n\n\n\n
6. \u7d22\u5f15\u4e0e\u67e5\u8be2\u4f18\u5316<\/strong><\/h3>\n\n\n\n
\u5047\u8bbe\u4f60\u6709\u4e00\u4e2a\u8868 employees<\/code>\uff0c\u5305\u542b\u5927\u91cf\u5458\u5de5\u6570\u636e\uff0c\u4f60\u53ef\u4ee5\u521b\u5efa\u7d22\u5f15\u6765\u63d0\u9ad8\u67e5\u8be2\u6548\u7387\u3002<\/p>\n\n\n\n
\u521b\u5efa\u7d22\u5f15<\/h4>\n\n\n\n
CREATE INDEX idx_employee_name ON employees(name);<\/code><\/pre>\n\n\n\n
\u4f7f\u7528 EXPLAIN<\/code> \u5206\u6790\u67e5\u8be2<\/h4>\n\n\n\n
\u5f53\u67e5\u8be2\u6267\u884c\u8f83\u6162\u65f6\uff0c\u53ef\u4ee5\u4f7f\u7528 EXPLAIN<\/code> \u67e5\u770b\u67e5\u8be2\u7684\u6267\u884c\u8ba1\u5212\uff1a<\/p>\n\n\n\n
EXPLAIN SELECT * FROM employees WHERE name = 'John';<\/code><\/pre>\n\n\n\n
EXPLAIN<\/code> \u5c06\u5c55\u793a\u67e5\u8be2\u662f\u5426\u5229\u7528\u4e86\u7d22\u5f15\u3001\u8868\u626b\u63cf\u7684\u987a\u5e8f\u7b49\u4fe1\u606f\u3002<\/p>\n\n\n\n
\n\n\n\n
7. \u590d\u6742\u67e5\u8be2\u4e0e\u5b50\u67e5\u8be2<\/strong><\/h3>\n\n\n\n
\u5b50\u67e5\u8be2\u5728 SELECT<\/code> \u4e2d\u4f7f\u7528<\/h4>\n\n\n\n
\u67e5\u8be2\u6bcf\u4e2a\u5b66\u751f\u548c\u4ed6\u4eec\u6240\u9009\u8bfe\u7a0b\u6570\u91cf\uff1a<\/p>\n\n\n\n
SELECT students.name, \n       (SELECT COUNT(*) FROM courses WHERE courses.student_id = students.id) AS course_count\nFROM students;<\/code><\/pre>\n\n\n\n
\u5b50\u67e5\u8be2\u5728 WHERE<\/code> \u4e2d\u4f7f\u7528<\/h4>\n\n\n\n
\u67e5\u8be2\u9500\u552e\u989d\u5927\u4e8e\u67d0\u4e2a\u5e73\u5747\u503c\u7684\u9500\u552e\u5458\uff1a<\/p>\n\n\n\n
SELECT salesperson\nFROM sales\nWHERE sales_amount > (SELECT AVG(sales_amount) FROM sales);<\/code><\/pre>\n\n\n\n
\n\n\n\n
\u603b\u7ed3<\/h3>\n\n\n\n
\u8fd9\u4e9b\u5b9e\u4f8b\u5c55\u793a\u4e86\u4ece\u7b80\u5355\u67e5\u8be2\u5230\u590d\u6742\u67e5\u8be2\u7684\u591a\u79cdSQL\u7528\u6cd5\uff0c\u5305\u62ec\u805a\u5408\u51fd\u6570\u3001\u8fde\u63a5\u67e5\u8be2\u3001\u7a97\u53e3\u51fd\u6570\u3001\u4e8b\u52a1\u7ba1\u7406\u7b49\u3002\u901a\u8fc7\u4e0d\u65ad\u5b9e\u8df5\u8fd9\u4e9b\u64cd\u4f5c\uff0c\u4f60\u53ef\u4ee5\u63d0\u5347SQL\u7684\u5e94\u7528\u80fd\u529b\uff0c\u9010\u6b65\u5e94\u5bf9\u66f4\u590d\u6742\u7684\u6570\u636e\u5e93\u64cd\u4f5c\u3002\u8981\u7279\u522b\u6ce8\u610f\u7684\u662f\uff0c\u7406\u89e3\u548c\u638c\u63e1SQL\u7684\u4f18\u5316\u6280\u5de7\uff0c\u80fd\u591f\u5e2e\u52a9\u4f60\u5e94\u5bf9\u5927\u6570\u636e\u91cf\u548c\u9ad8\u5e76\u53d1\u7684\u67e5\u8be2\u9700\u6c42\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u597d\u7684\uff01\u4e3a\u4e86\u5e2e\u52a9\u4f60\u66f4\u597d\u5730\u7406\u89e3\u548c\u638c\u63e1SQL\uff0c\u4ee5\u4e0b\u662f\u51e0\u4e2a\u5b9e\u7528\u7684SQL\u5b9e\u4f8b\uff0c\u6db5\u76d6\u4e86\u57fa\u7840\u67e5\u8be2\u3001\u590d\u6742\u67e5\u8be2\u3001\u7a97\u53e3\u51fd\u6570\u3001\u4e8b\u52a1\u7ba1 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[36],"tags":[],"class_list":["post-619","post","type-post","status-publish","format-standard","hentry","category-sql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/619","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=619"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/619\/revisions"}],"predecessor-version":[{"id":620,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/619\/revisions\/620"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=619"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=619"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=619"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}