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  • mysql笔记

    创建数据库

    create database dbtest1

    查询数据库通用语法:

    select columnName,columnName1 from dbname.tablename [where clause] [order by] [limit N];

    查看表格所有列:

    select * from dbname.tablename;

    查看某一列和:

    select SUM(columnName) from dbname.tableName;

    多表联合查找

    select table1.column1,table1.column2 from table1 left join table2 on table1.column3=table2.column3 where table1.column4='test';//left join以左表为主,获取左表所有记录,即使右表没有匹配记录,
    right join相反,以右表为主,获取右表所有记录,inner join则获取量表中字段完全匹配关系的记录

    单一条件联合查找

    select * from table 1 where column1 = (select column1 from table2 where column3>0);

    条件查找之if语句

    select ( case
        when column1 + column2 = column3 then 'true'
            when column1 + column2 != column3 then 'false'
    end) as result from table1 where column>0;

    查看表行数

    select count(*) from table1;

    排序,限行数

    select * from table1 order by column1 desc limit 10; //按column1倒叙排列,取前10行
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  • 原文地址:https://www.cnblogs.com/testerLydia/p/9464080.html
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