MySQL随笔

1. 一句话实现Mysql查询结果带行号   

SELECT @rowno:=@rowno+1 AS rowno,a.id,a.`status`,a.reason FROM e_four_auth a,(SELECT @rowno:=0) b

 (SELECT @rowno:=0) 初始化rowno   ； @rowno:=@rowno+1 每行+1

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2.explain 用法和结果的含义

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1 inner join : SELECT * FROM TableA INNER JOIN TableB ON TableA.name = TableB.name 

交集

2 left join : SELECT * FROM TableA LEFT JOIN TableB ON TableA.name = TableB.name

A的完全集，B中能匹配的则有值，没有匹配的则null. (right left类似。不写了)

SELECT * FROM TableA LEFT JOIN TableB ON TableA.name = TableB.name WHERE TableB.id IS NULL;

A中有，B中没有的

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