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  • 【面试虐菜】—— 常用SQL语句

    创建表

    create table emp(
    
    id decimal,
    
    name char(10),
    
    age decimal)

    删除表

    DROP TABLE EMP

    插入默认值

    CREATE TABLE EMP(
    
      Id decimal NOT NULL,
    
      Name char(10) NOT NULL,
    
      Age decimal NOT NULL DEFAULT 18)

    添加列

    ALTER TABLE EMP ADD COLUMN Comments char(50) NOT NULL DEFAULT 'COMMENTS'

    删除列

    ALTER TABLE EMP DROP COLUMN Comments

    修改列

    ALTER TABLE EMP MODIFY COLUMN Comments char(30)

    创建索引

    CREATE INDEX Name_index ON EMP (Name)

    查询数据

    SELECT Name FROM EMP

    查询不重复的数据

    SELECT DISTINCT Name FROM EMP

    对查询结果排序

    SELECT Name FROM EMP ORDER BY Name

    条件查询

    SELECT Name FROM EMP WHERE Age < 20
    
    SELECT Name FROM EMP WHERE Age BETWEEN 20 AND 30

    插入数据

    INSERT INTO EMP VALUES(123,'xingoo',18)

    修改数据

    UPDATE EMP SET Name='xingoo1111' WHERE Name='xingoo'

    删除数据

    DELETE FROM EMP WHERE Age<20

    求平均数

    SELECT AVG(Age) FROM EMP

    查询条数

    SELECT COUNT(DISTINCT Name) FROM EMP
    
    SELECT COUNT(*) FROM EMP
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  • 原文地址:https://www.cnblogs.com/xing901022/p/3975705.html
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