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fix(docs): escaping the '*' chars in the doc to prevent rendering error #1005

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fix(docs): escaping the '*' chars in the doc to prevent rendering error #1005

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4 changes: 2 additions & 2 deletions p3c-gitbook/MySQL数据库/SQL语句.md
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## (三) SQL语句
1. 【强制】不要使用count(列名)或count(常量)来替代count(*)，count(*)是SQL92定义的标准统计行数的语法，跟数据库无关，跟NULL和非NULL无关。
1. 【强制】不要使用count(列名)或count(常量)来替代count(\*)，count(\*)是SQL92定义的标准统计行数的语法，跟数据库无关，跟NULL和非NULL无关。
<br><span style="color:orange">说明</span>：count(*)会统计值为NULL的行，而count(列名)不会统计此列为NULL值的行。
2. 【强制】count(distinct col) 计算该列除NULL之外的不重复行数，注意 count(distinct col1, col2) 如果其中一列全为NULL，那么即使另一列有不同的值，也返回为0。
3. 【强制】当某一列的值全是NULL时，count(col)的返回结果为0，但sum(col)的返回结果为NULL，因此使用sum()时需注意NPE问题。
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SELECT CHARACTER_LENGTH("轻松工作")； 返回为4</pre>
如果需要存储表情，那么选择utf8mb4来进行存储，注意它与utf-8编码的区别。
11. 【参考】 TRUNCATE TABLE 比 DELETE 速度快，且使用的系统和事务日志资源少，但TRUNCATE无事务且不触发trigger，有可能造成事故，故不建议在开发代码中使用此语句。
<br><span style="color:orange">说明</span>：TRUNCATE TABLE 在功能上与不带 WHERE 子句的 DELETE 语句相同。
<br><span style="color:orange">说明</span>：TRUNCATE TABLE 在功能上与不带 WHERE 子句的 DELETE 语句相同。