mysql

基本查询

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SELECT * FROM student;

select为关键字

*表示所有列(或为列名称)

student为要查的表

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SELECT <定义列的名字> FROM <表名>;
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SELECT 1 ;  #测试数据库链接

条件查询

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SELECT * FROM <表名> WHERE <条件表达式>;
/*
AND
OR
NOT
<> #!=
组合可用()
*/

排序

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SELECT * FROM students ORDER BY score;
#将表student按score从小到大排序
SELECT * FROM students ORDER BY score DESC;#从大到小
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SELECT *
FROM students
WHERE class_id = 1
ORDER BY score DESC;

分页

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SELECT id, name, gender, score
FROM students
ORDER BY score DESC
LIMIT 3 OFFSET 6;
#从第6条截取3个

聚合查询

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SELECT COUNT(*) FROM students;
#查询students一共几条
SELECT COUNT(*) num FROM students;#将行数起名num
SELECT COUNT(*) num FROM students GROUP BY class_id;#按class_id分组

插入

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INSERT INTO students (字段1, 字段2, ...) VALUES (值1, 值2, ...);
-- 查询并观察结果:
SELECT * FROM students;