Mysql读语句优化一些好的习惯----yueliangdao0608

GIS_Cloud 2011-10-26 03:38:17

加精

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

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