计算 datediff 时的差异 MySQL

Question

我在一个案例和一个地方使用 datediff 时得到不同的结果。这是 table 用户，省略了不相关的列，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>

当运行宁此：

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>&lt; 21</td></tr><tr><td>1</td><td>&gt; 51</td></tr><tr><td>7</td><td>Sin Registro</td></tr></tbody></table>

但是当我运行:

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

SQLFiddle with complete tables and data.

Answer 1

手动检查结果后，我发现两者都不正确。将 FLOOR() 添加到 datediff 结果，最终给出了正确的结果。

最终查询：

SELECT COUNT(users.UserID), case   when users.UserBirthDate IS NULL  then  'Sin Registro'  
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 50  then  '> 51' 
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 40 AND  FLOOR(datediff(now(), users.UserBirthDate) / 365.25) < 51 then  '41 - 50'  
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 30 AND  FLOOR(datediff(now(), users.UserBirthDate) / 365.25) < 41 then  '31 - 40'  
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 26 AND  FLOOR(datediff(now(), users.UserBirthDate) / 365.25) < 31 then  '27 - 30'  
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 20 AND  FLOOR(datediff(now(), users.UserBirthDate) / 365.25) < 27 then  '21 - 26'  
when FLOOR(datediff(now(), users.UserBirthDate) / 365.25) <= 20  then  '< 21'  end as AgeGroup FROM users GROUP BY AgeGroup;

正确结果：

<table><tbody><tr><th>COUNT(users.userid)</th><th>AgeGroup</th></tr><tr><td>4</td><td>21 - 26</td></tr><tr><td>1</td><td>27 - 30</td></tr><tr><td>2</td><td>31 - 40</td></tr><tr><td>4</td><td>&lt; 21</td></tr><tr><td>1</td><td>&gt; 51</td></tr><tr><td>7</td><td>Sin Registro</td></tr></tbody></table>

用where + floor检查，我也得到了正确的结果。

SELECT COUNT(users.UserID) 
FROM users
WHERE FLOOR(datediff(now(), users.UserBirthDate) / 365.25) > 20 AND  FLOOR(datediff(now(), users.UserBirthDate) / 365.25) < 27;

Returns4个，喜欢的话

我想由于大小写顺序的原因，大小写与 where 不同。

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