mysql using the function STR_TO_DATE () stepped pit

1, in the practical application projects you need to query the last full month of data, because of his previous projects with similar queries. So we use STR_TO_DATE function as a condition. It was found that using the wrong one. WRONG:

SELECT
       COUNT(1)
FROM
     tf_u_user
WHERE
    CREATE_TIME >= STR_TO_DATE('2019-04','%Y-%m')
                      AND
                      CREATE_TIME < STR_TO_DATE('2019-05', '%Y-%m');

　The problem with this method is that STR_TO_DATE () when this function, the date format is not only to format the date, the date will be formatted, such STR_TO_DATE ( '2019-04', '% Y-% m') It is equivalent to '2019-03-31'. Therefore, an error occurred.

select  STR_TO_DATE('2019-04','%Y-%m'); --- “2019-03-31”

Use this query to find and expected results are not the same, so using another method.

SELECT * FROM tf_u_user WHERE PERIOD_DIFF(date_format(NOW(),'%Y%m' ) , date_format(CREATE_TIME,'%Y%m')) =1;

Optimization and added:

　　Use this method resolved STR_TO_DATE () function in the pit, but can only query data last month, and that if the investigation phase last month how to do, and then a little earlier data is what to do?

1 may be modified as = = 2 and the like.

Of course, this is just one way. Not the best. But effective in actual use, at the same time I want to record this pit. To do this as a reminder. Any function of time in the next test. We can not rely on experience.

Also this error is not enough on its own understanding STR_TO_DATE this function, it shall not be treated using the method, if it is written the date is also possible.

SELECT
       COUNT(1)
FROM
     tf_u_user
WHERE
    CREATE_TIME >= STR_TO_DATE('2019-04-01','%Y-%m-%d')
                      AND
                      CREATE_TIME < STR_TO_DATE('2019-05-01', '%Y-%m-%d');

Such queries can also write data in April. You may be specifically selected depending on the application.