Common mysql statements at work can be achieved without using php.

1. Calculate the number of years
You figured out how old this person is on your birthday. Copy codeThe Code is as follows: SELECT DATE_FORMAT (FROM_DAYS (TO_DAYS (now ()-TO_DAYS (@ dateofbirth), '% y') + 0;

2. Difference between two time points
Returns the difference between two datetime values. Assume that dt1 and dt2 are of the datetime type, and their format is 'yyyy-mm-dd hh: mm: ss'. The difference between them is:
UNIX_TIMESTAMP (dt2)-UNIX_TIMESTAMP (dt1) divided by 60 is the number of minutes in the difference, divided by 3600 is the number of hours in the difference, and then divided by 24 is the number of days in the difference.
3. display the value of a column that appears N times
Copy codeThe Code is as follows: SELECT id
FROM tbl
Group by id
Having count (*) = N;

4. Calculate the workdays between two days
Workdays are divided into Saturday and Sunday holidays.Copy codeThe Code is as follows: select count (*)
FROM calendar
WHERE d BETWEEN Start AND Stop
And dayofweek (d) not in (1, 7)
AND holiday = 0;

5. Search for the primary key in the table Copy codeThe Code is as follows: SELECT k. column_name
FROM information_schema.table_constraints t
JOIN information_schema.key_column_usage k
USING (constraint_name, table_schema, table_name)
WHERE t. constraint_type = 'Primary key'
AND t. table_schema = 'db'
AND t. table_name = tbl'

6. Check the size of your database. Copy codeThe Code is as follows: ELECT
Table_schema AS 'db name ',
Round (Sum (data_length + index_length)/1024/1024, 3) AS 'db Size (MB )',
Round (Sum (data_free)/1024/1024, 3) AS 'free Space (MB )'
FROM information_schema.tables
Group by table_schema;