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DATABASE [IF EXISTS] database_name;\n",[48,122,123],{"__ignoreMap":46},[51,124,125],{"class":53,"line":54},[51,126,120],{},[28,128,129,93],{},[90,130,92],{},[41,132,134],{"className":43,"code":133,"language":45,"meta":46,"style":46},"DROP DATABASE IF EXISTS test_db;\n",[48,135,136],{"__ignoreMap":46},[51,137,138],{"class":53,"line":54},[51,139,133],{},[141,142,143],"blockquote",{},[28,144,145,148],{},[90,146,147],{},"注意","：删除数据库是不可逆操作，会删除其中所有表和数据。",[36,150,152],{"id":151},"_3-修改数据库字符集","3. 修改数据库字符集",[41,154,156],{"className":43,"code":155,"language":45,"meta":46,"style":46},"ALTER DATABASE database_name\n  CHARACTER SET new_charset\n  COLLATE new_collation;\n",[48,157,158,163,168],{"__ignoreMap":46},[51,159,160],{"class":53,"line":54},[51,161,162],{},"ALTER DATABASE database_name\n",[51,164,165],{"class":53,"line":60},[51,166,167],{},"  CHARACTER SET new_charset\n",[51,169,170],{"class":53,"line":66},[51,171,172],{},"  COLLATE 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(\n",[51,215,216],{"class":53,"line":60},[51,217,218],{},"    column1 datatype [constraints],\n",[51,220,221],{"class":53,"line":66},[51,222,223],{},"    column2 datatype [constraints],\n",[51,225,227],{"class":53,"line":226},4,[51,228,229],{},"    ...\n",[51,231,233],{"class":53,"line":232},5,[51,234,235],{},"    [table_constraints]\n",[51,237,239],{"class":53,"line":238},6,[51,240,241],{},") [ENGINE=engine] [CHARACTER SET charset];\n",[28,243,244,246,247,250],{},[90,245,92],{},"：创建 ",[48,248,249],{},"students"," 表",[41,252,254],{"className":43,"code":253,"language":45,"meta":46,"style":46},"CREATE TABLE students (\n    id INT PRIMARY KEY AUTO_INCREMENT,\n    name VARCHAR(50) NOT NULL,\n    age TINYINT UNSIGNED,\n    grade DECIMAL(5,2),\n    created_at DATETIME DEFAULT CURRENT_TIMESTAMP\n) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;\n",[48,255,256,261,266,271,276,281,286],{"__ignoreMap":46},[51,257,258],{"class":53,"line":54},[51,259,260],{},"CREATE TABLE students (\n",[51,262,263],{"class":53,"line":60},[51,264,265],{},"    id INT PRIMARY KEY AUTO_INCREMENT,\n",[51,267,268],{"class":53,"line":66},[51,269,270],{},"    name VARCHAR(50) NOT NULL,\n",[51,272,273],{"class":53,"line":226},[51,274,275],{},"    age TINYINT UNSIGNED,\n",[51,277,278],{"class":53,"line":232},[51,279,280],{},"    grade DECIMAL(5,2),\n",[51,282,283],{"class":53,"line":238},[51,284,285],{},"    created_at DATETIME DEFAULT CURRENT_TIMESTAMP\n",[51,287,289],{"class":53,"line":288},7,[51,290,291],{},") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;\n",[28,293,294],{},"常见约束：",[71,296,297,303,309,315,321,327],{},[74,298,299,302],{},[48,300,301],{},"PRIMARY KEY","：主键",[74,304,305,308],{},[48,306,307],{},"AUTO_INCREMENT","：自增（通常用于主键）",[74,310,311,314],{},[48,312,313],{},"NOT NULL","：不能为空",[74,316,317,320],{},[48,318,319],{},"UNIQUE","：值唯一",[74,322,323,326],{},[48,324,325],{},"DEFAULT","：默认值",[74,328,329,332],{},[48,330,331],{},"CHECK","：检查约束（MySQL 8.0+ 支持）",[36,334,336],{"id":335},"_2-删除表","2. 删除表",[41,338,340],{"className":43,"code":339,"language":45,"meta":46,"style":46},"DROP TABLE [IF EXISTS] table_name;\n",[48,341,342],{"__ignoreMap":46},[51,343,344],{"class":53,"line":54},[51,345,339],{},[28,347,348,93],{},[90,349,92],{},[41,351,353],{"className":43,"code":352,"language":45,"meta":46,"style":46},"DROP TABLE IF EXISTS temp_table;\n",[48,354,355],{"__ignoreMap":46},[51,356,357],{"class":53,"line":54},[51,358,352],{},[36,360,362],{"id":361},"_3-修改表结构alter-table","3. 修改表结构（ALTER TABLE）",[364,365,366],"h5",{"id":366},"增加列",[41,368,370],{"className":43,"code":369,"language":45,"meta":46,"style":46},"ALTER TABLE table_name ADD column_name datatype [constraints] [FIRST | AFTER column];\n",[48,371,372],{"__ignoreMap":46},[51,373,374],{"class":53,"line":54},[51,375,369],{},[28,377,378,380,381,383,384,387],{},[90,379,92],{},"：在 ",[48,382,249],{}," 表中增加 ",[48,385,386],{},"email"," 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[constraints];\n",[48,430,431],{"__ignoreMap":46},[51,432,433],{"class":53,"line":54},[51,434,428],{},[28,436,437,439,440,443],{},[90,438,92],{},"：将 ",[48,441,442],{},"name"," 列的长度从 50 改为 100",[41,445,447],{"className":43,"code":446,"language":45,"meta":46,"style":46},"ALTER TABLE students MODIFY name VARCHAR(100) NOT NULL;\n",[48,448,449],{"__ignoreMap":46},[51,450,451],{"class":53,"line":54},[51,452,446],{},[364,454,456],{"id":455},"重命名列change","重命名列（CHANGE）",[41,458,460],{"className":43,"code":459,"language":45,"meta":46,"style":46},"ALTER TABLE table_name CHANGE old_name new_name new_datatype [constraints];\n",[48,461,462],{"__ignoreMap":46},[51,463,464],{"class":53,"line":54},[51,465,459],{},[28,467,468,439,470,473,474,477,478],{},[90,469,92],{},[48,471,472],{},"grade"," 列重命名为 ",[48,475,476],{},"score","，同时修改类型为 ",[48,479,480],{},"DECIMAL(6,2)",[41,482,484],{"className":43,"code":483,"language":45,"meta":46,"style":46},"ALTER TABLE students CHANGE grade score DECIMAL(6,2);\n",[48,485,486],{"__ignoreMap":46},[51,487,488],{"class":53,"line":54},[51,489,483],{},[364,491,492],{"id":492},"重命名表",[41,494,496],{"className":43,"code":495,"language":45,"meta":46,"style":46},"RENAME TABLE old_name TO new_name;\n",[48,497,498],{"__ignoreMap":46},[51,499,500],{"class":53,"line":54},[51,501,495],{},[28,503,504,93],{},[90,505,92],{},[41,507,509],{"className":43,"code":508,"language":45,"meta":46,"style":46},"RENAME TABLE students TO pupils;\n",[48,510,511],{"__ignoreMap":46},[51,512,513],{"class":53,"line":54},[51,514,508],{},[28,516,517,518,93],{},"也可以使用 ",[48,519,520],{},"ALTER TABLE",[41,522,524],{"className":43,"code":523,"language":45,"meta":46,"style":46},"ALTER TABLE old_name RENAME TO new_name;\n",[48,525,526],{"__ignoreMap":46},[51,527,528],{"class":53,"line":54},[51,529,523],{},[31,531,533],{"id":532},"三补充操作","三、补充操作",[36,535,536],{"id":536},"查看表结构",[41,538,540],{"className":43,"code":539,"language":45,"meta":46,"style":46},"DESC table_name;          -- 简洁版\nSHOW FULL COLUMNS FROM table_name;  -- 详细信息\n",[48,541,542,547],{"__ignoreMap":46},[51,543,544],{"class":53,"line":54},[51,545,546],{},"DESC table_name;          -- 简洁版\n",[51,548,549],{"class":53,"line":60},[51,550,551],{},"SHOW FULL COLUMNS FROM table_name;  -- 详细信息\n",[36,553,554],{"id":554},"查看创建表的语句",[41,556,558],{"className":43,"code":557,"language":45,"meta":46,"style":46},"SHOW CREATE TABLE table_name;\n",[48,559,560],{"__ignoreMap":46},[51,561,562],{"class":53,"line":54},[51,563,557],{},[36,565,567],{"id":566},"复制表结构不复制数据","复制表结构（不复制数据）",[41,569,571],{"className":43,"code":570,"language":45,"meta":46,"style":46},"CREATE TABLE new_table LIKE original_table;\n",[48,572,573],{"__ignoreMap":46},[51,574,575],{"class":53,"line":54},[51,576,570],{},[36,578,579],{"id":579},"复制表结构和数据",[41,581,583],{"className":43,"code":582,"language":45,"meta":46,"style":46},"CREATE TABLE new_table AS SELECT * FROM original_table;\n",[48,584,585],{"__ignoreMap":46},[51,586,587],{"class":53,"line":54},[51,588,582],{},[36,590,592],{"id":591},"清空表删除所有行保留结构","清空表（删除所有行，保留结构）",[41,594,596],{"className":43,"code":595,"language":45,"meta":46,"style":46},"TRUNCATE TABLE table_name;\n",[48,597,598],{"__ignoreMap":46},[51,599,600],{"class":53,"line":54},[51,601,595],{},[141,603,604],{},[28,605,606,609,610,613],{},[48,607,608],{},"TRUNCATE"," 比 ",[48,611,612],{},"DELETE FROM table_name"," 更快，但无法回退（事务性差），且会重置自增计数器。",[31,615,617],{"id":616},"四注意事项","四、注意事项",[619,620,621,631,640,650,656],"ol",{},[74,622,623,626,627,630],{},[90,624,625],{},"命名规范","：数据库名、表名、列名建议使用小写字母 + 下划线（如 ",[48,628,629],{},"user_info","），避免使用 SQL 保留字。",[74,632,633,636,637,639],{},[90,634,635],{},"字符集","：建库时指定 ",[48,638,85],{}," 可避免中文或 emoji 乱码。",[74,641,642,645,646,649],{},[90,643,644],{},"InnoDB 引擎","：推荐使用 ",[48,647,648],{},"InnoDB","，支持事务、外键、行级锁。",[74,651,652,655],{},[90,653,654],{},"IF EXISTS \u002F IF NOT EXISTS","：在自动化脚本中建议加上，防止因对象不存在或重复创建而报错。",[74,657,658,661,662,665,666,669],{},[90,659,660],{},"修改列类型（MODIFY\u002FCHANGE）","：可能会导致数据丢失（如将 ",[48,663,664],{},"VARCHAR"," 改为 ",[48,667,668],{},"INT"," 且原数据非数字），谨慎操作。",[31,671,673],{"id":672},"五综合示例","五、综合示例",[41,675,677],{"className":43,"code":676,"language":45,"meta":46,"style":46},"-- 创建数据库\nCREATE DATABASE IF NOT EXISTS company\n  CHARACTER SET utf8mb4\n  COLLATE utf8mb4_unicode_ci;\n\n-- 使用数据库\nUSE company;\n\n-- 创建表\nCREATE TABLE employees (\n    id INT PRIMARY KEY AUTO_INCREMENT,\n    emp_name VARCHAR(50) NOT NULL,\n    department_id INT,\n    salary DECIMAL(10,2) NOT NULL,\n    hire_date DATE,\n    status TINYINT DEFAULT 1\n);\n\n-- 增加列\nALTER TABLE employees ADD email VARCHAR(100);\n\n-- 修改列类型\nALTER TABLE employees MODIFY email VARCHAR(200);\n\n-- 重命名列\nALTER TABLE employees CHANGE emp_name full_name VARCHAR(50);\n\n-- 重命名表\nRENAME TABLE employees TO staff;\n\n-- 删除表（谨慎）\nDROP TABLE IF EXISTS staff;\n",[48,678,679,684,689,693,697,703,708,713,718,724,730,735,741,747,753,759,765,771,776,782,788,793,799,805,810,816,822,827,833,839,844,850],{"__ignoreMap":46},[51,680,681],{"class":53,"line":54},[51,682,683],{},"-- 创建数据库\n",[51,685,686],{"class":53,"line":60},[51,687,688],{},"CREATE DATABASE IF NOT EXISTS company\n",[51,690,691],{"class":53,"line":66},[51,692,108],{},[51,694,695],{"class":53,"line":226},[51,696,113],{},[51,698,699],{"class":53,"line":232},[51,700,702],{"emptyLinePlaceholder":701},true,"\n",[51,704,705],{"class":53,"line":238},[51,706,707],{},"-- 使用数据库\n",[51,709,710],{"class":53,"line":288},[51,711,712],{},"USE company;\n",[51,714,716],{"class":53,"line":715},8,[51,717,702],{"emptyLinePlaceholder":701},[51,719,721],{"class":53,"line":720},9,[51,722,723],{},"-- 创建表\n",[51,725,727],{"class":53,"line":726},10,[51,728,729],{},"CREATE TABLE employees (\n",[51,731,733],{"class":53,"line":732},11,[51,734,265],{},[51,736,738],{"class":53,"line":737},12,[51,739,740],{},"    emp_name VARCHAR(50) NOT NULL,\n",[51,742,744],{"class":53,"line":743},13,[51,745,746],{},"    department_id INT,\n",[51,748,750],{"class":53,"line":749},14,[51,751,752],{},"    salary DECIMAL(10,2) NOT NULL,\n",[51,754,756],{"class":53,"line":755},15,[51,757,758],{},"    hire_date DATE,\n",[51,760,762],{"class":53,"line":761},16,[51,763,764],{},"    status TINYINT DEFAULT 1\n",[51,766,768],{"class":53,"line":767},17,[51,769,770],{},");\n",[51,772,774],{"class":53,"line":773},18,[51,775,702],{"emptyLinePlaceholder":701},[51,777,779],{"class":53,"line":778},19,[51,780,781],{},"-- 增加列\n",[51,783,785],{"class":53,"line":784},20,[51,786,787],{},"ALTER TABLE employees ADD email VARCHAR(100);\n",[51,789,791],{"class":53,"line":790},21,[51,792,702],{"emptyLinePlaceholder":701},[51,794,796],{"class":53,"line":795},22,[51,797,798],{},"-- 修改列类型\n",[51,800,802],{"class":53,"line":801},23,[51,803,804],{},"ALTER TABLE employees MODIFY email 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