计算datediff MySQL时的差异
计算datediff MySQL时的差异
提问于 2016-02-07 00:24:07
在使用datediff时，我会得到不同的结果。这是表用户，省略了不相关的列，并对所有用户：
<table><tbody><tr><th>UserID</th><th>UserTypeID</th><th>UserRegistrationDate</th><th>UserBirthDate</th><th>UserJobID</th><th>UserLocationID</th></tr><tr><td>1</td><td>1</td><td> </td><td> </td><td> </td><td> </td></tr><tr><td>2</td><td>1</td><td>3/12/2015</td><td>30/1/1982</td><td>2</td><td>3</td></tr><tr><td>3</td><td>1</td><td>2/12/2015</td><td>19/9/1987</td><td>2</td><td>4</td></tr><tr><td>12</td><td>1</td><td>2/12/2015</td><td>11/9/1992</td><td>2</td><td>5</td></tr><tr><td>13</td><td>1</td><td>13/12/2015</td><td>15/5/1995</td><td>2</td><td>2</td></tr><tr><td>40</td><td>1</td><td>10/1/2016</td><td>22/7/1975</td><td>2</td><td>2</td></tr><tr><td>47</td><td>1</td><td>16/1/2016</td><td>29/2/2000</td><td>1</td><td>6</td></tr><tr><td>50</td><td> </td><td> </td><td>1/12/1956</td><td>2</td><td>2</td></tr><tr><td>52</td><td> </td><td> </td><td>12/3/1998</td><td>2</td><td>6</td></tr><tr><td>54</td><td>1</td><td>20/1/2016</td><td>11/4/1990</td><td>2</td><td>2</td></tr><tr><td>55</td><td>1</td><td>25/1/2016</td><td> </td><td> </td><td> </td></tr><tr><td>57</td><td> </td><td> </td><td>1/1/1990</td><td> </td><td> </td></tr><tr><td>58</td><td>1</td><td> </td><td> </td><td> </td><td> </td></tr><tr><td>59</td><td>1</td><td>28/1/2016</td><td> </td><td> </td><td> </td></tr><tr><td>60</td><td>1</td><td>13/1/2016</td><td>1/1/1998</td><td>1</td><td>10</td></tr><tr><td>61</td><td>1</td><td>1/12/2015</td><td>22/6/1989</td><td>1</td><td>12</td></tr><tr><td>66</td><td>1</td><td>1/2/2016</td><td> </td><td> </td><td> </td></tr><tr><td>67</td><td>1</td><td>1/2/2016</td><td> </td><td> </td><td> </td></tr><tr><td>68</td><td>1</td><td>1/2/2016</td><td> </td><td> </td><td> </td></tr></tbody></table>
运行此程序时：
SELECT
COUNT(users.UserID),
CASE WHEN users.UserBirthDate IS NULL
THEN 'Sin Registro'
WHEN datediff(now(), users.UserBirthDate) / 365.25 > 50
THEN '> 51'
WHEN datediff(now(), users.UserBirthDate) / 365.25 > 40 AND datediff(now(), users.UserBirthDate) / 365.25 < 51
THEN '41 - 50'
WHEN datediff(now(), users.UserBirthDate) / 365.25 > 30 AND datediff(now(), users.UserBirthDate) / 365.25 < 41
THEN '31 - 40'
WHEN datediff(now(), users.UserBirthDate) / 365.25 > 26 AND datediff(now(), users.UserBirthDate) / 365.25 < 31
THEN '27 - 30'
WHEN datediff(now(), users.UserBirthDate) / 365.25 > 20 AND datediff(now(), users.UserBirthDate) / 365.25 < 27
THEN '21 - 26'
WHEN datediff(now(), users.UserBirthDate) / 365.25 <= 20
THEN '< 21' END AS AgeGroup
FROM users
GROUP BY AgeGroup我得到了这个结果：
<table><tbody><tr><th>COUNT(users.userid)</th><th>AgeGroup</th></tr><tr><td>3</td><td>21 - 26</td></tr><tr><td>3</td><td>27 - 30</td></tr><tr><td>1</td><td>31 - 40</td></tr><tr><td>1</td><td>41 - 50</td></tr><tr><td>3</td><td>< 21</td></tr><tr><td>1</td><td>> 51</td></tr><tr><td>7</td><td>Sin Registro</td></tr></tbody></table>
但当我跑的时候
SELECT COUNT(users.UserID)
FROM users
WHERE datediff(now(), users.UserBirthDate) / 365.25 > 20 AND datediff(now(), users.UserBirthDate) / 365.25 < 27;我明白了：
<table><tbody><tr><th>COUNT(users.userid)</th></tr><tr><td>5</td></tr></tbody></table>
更新
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/35248263
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