Mysql读语句优化一些好的习惯----yueliangdao0608
1、
SELECT * FROM t WHERE YEAR(d) >= 1994;
SELECT * FROM t WHERE d >= '1994-01-01';//这个好,相比上面的语句没有用year函数,
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2、
SELECT * FROM Country ,CountryLanguage
WHERE Country.Code= CountryLanguage.CountryCode;
SELECT * FROM Country JOIN CountryLanguage
ON Country.Code= CountryLanguage.CountryCode;//这个好,显式说明了连接关系,以前好像在哪里看到过,记不起来了
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3、
SELECT * FROM t WHERE id = ‘19’;
SELECT * FROM t WHERE id = 19;//id 设置成int类型的要比char或者archar的好?不是很明白
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4、
SELECT * FROM t WHERE length(column_t) = 5;
SELECT * FROM t WHERE column_length=5; //这个也不明白
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5、
SELECT * FROM t WHERE name LIKE '%de%‘
SELECT * FROM t WHERE name LIKE 'de%'
SELECT * FROM t WHERE name >= 'de' AND name < 'df‘//将like查询改成非like查询?具体例子什么意思不清楚
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6、
SELECT * FROM t WHERE 1;
SELECT * FROM t WHERE 1 LIMIT 10;这个也不懂
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7、
SELECT * FROM Country WHERE Name LIKE 'M%';
SELECT Name FROM Country WHERE Name LIKE 'M%';//只取需要的字段
在看yueliangdao0608的Mysql开发与优化的ppt时,看到了上面的sql,所以拿出来请教下