[MySQL series] collection of common working SQL (continuous update)

Summarize the commonly used sql.

Get the current time in milliseconds

be used CURRENT_TIMESTAMP(3).

select CURRENT_TIMESTAMP(3);

However, when specifying fields, you need to note that the field type also needs to datatime(3) type .

In the field type ,datetime(3) It is accurate to the millisecond level ,datetime The default is 0, Accurate to the second level .

How to count the total number of interface calls ？

use group by, Such as

SELECT
	service,
	app_key,
	count(*) 
FROM
	trace_log t 
WHERE
	create_time BETWEEN '2020-04-01 00:00' 
	AND '2020-05-01 00:00' 
GROUP BY
	service,
	app_key;

The number of entries in the statistical table exceeds 2 Data for

With aggregate functions having

SELECT
	service,
  app_key
FROM
	aa 
GROUP BY
	service 
HAVING
	count( * ) > 1;

Query second place

Use the less than sign , This will rule out null

SELECT
	max( VALUE ) 
FROM
	customer 
WHERE
	VALUE
		< ( SELECT max( VALUE ) FROM customer );