MySQL Query for first Datetime Item of a Day - mysql
I've got a Database in MySQL with around 1,000,000 DateTime Entries (Format: 2022-01-31 19:45:39) and so on.
For each day I have 100 Entries. I need a query to get the first DateTime Entry of the day, for the last 30 Days, where Column Number = 1234.
In PostgreSQl I would use a Lateral Join, but how to deal with it in MySQL?
Schema:
id int(11) auto_increment
datetime datetime
number varchar(255)
Someone can give me a full working example? I can't get it working
Related
How to count entries in a mysql table grouped by time
I've found lots of not quite the answers to this question, but nothing I can base my rather limited sql skills on... I've got a gas meter, which gives a pulse every cm3 of gas used - the time the pulses happen is obtained by a pi and stored in a mysql db. I'm trying to graph the db. In order to graph the data, I want to sum how many pulses are received every n time period. Where n may be 5 mins for a graph covering a day or n may be up to 24hours for a graph covering a year. The data are in a table which has two columns, a primary key/auto inc called "pulse_ref" and "pulse_time" which stores a unix timestamp of the time a pulse was received. Can anyone suggest a sql query to count how many pulses occurred grouped up into, say, 5minutely intervals? Create table: CREATE TABLE `gas_pulse` ( `pulse_ref` int(11) NOT NULL AUTO_INCREMENT, `pulse_time` int(11) DEFAULT NULL, PRIMARY KEY (`pulse_ref`)); Populate some data: INSERT INTO `gas_pulse` VALUES (1,1477978978),(2,1477978984),(3,1477978990),(4,1477978993),(5,1477979016),(6,1477979063),(7,1477979111),(8,1477979147),(9,1477979173),(10,1477979195),(11,1477979214),(12,1477979232),(13,1477979249),(14,1477979267),(15,1477979285),(16,1477979302),(17,1477979320),(18,1477979337),(19,1477979355),(20,1477979372),(21,1477979390),(22,1477979408),(23,1477979425),(24,1477979443),(25,1477979461),(26,1477979479),(27,1477979497),(28,1477979515),(29,1477979533),(30,1477979551),(31,1477979568),(32,1477979586),(33,1477980142),(34,1477980166),(35,1477981433),(36,1477981474),(37,1477981526),(38,1477981569),(39,1477981602),(40,1477981641),(41,1477981682),(42,1477981725),(43,1477981770),(44,1477981816),(45,1477981865),(46,1477981915),(47,1477981966),(48,1477982017),(49,1477982070),(50,1477982124),(51,1477982178),(52,1477982233),(53,1477988261),(54,1477988907),(55,1478001784),(56,1478001807),(57,1478002385),(58,1478002408),(59,1478002458),(60,1478002703),(61,1478002734),(62,1478002784),(63,1478002831),(64,1478002863),(65,1478002888),(66,1478002909),(67,1478002928),(68,1478002946),(69,1478002964),(70,1478002982),(71,1478003000),(72,1478003018),(73,1478003036),(74,1478003054),(75,1478003072),(76,1478003090),(77,1478003108),(78,1478003126),(79,1478003145),(80,1478003163),(81,1478003181),(82,1478003199),(83,1478003217),(84,1478003235),(85,1478003254),(86,1478003272),(87,1478003290),(88,1478003309),(89,1478003327),(90,1478003346),(91,1478003366),(92,1478003383),(93,1478003401),(94,1478003420),(95,1478003438),(96,1478003457),(97,1478003476),(98,1478003495),(99,1478003514),(100,1478003533),(101,1478003552),(102,1478003572),(103,1478003592),(104,1478003611),(105,1478003632),(106,1478003652),(107,1478003672),(108,1478003693),(109,1478003714),(110,1478003735),(111,1478003756),(112,1478003778),(113,1478003799),(114,1478003821),(115,1478003844),(116,1478003866),(117,1478003889),(118,1478003912),(119,1478003936),(120,1478003960),(121,1478003984),(122,1478004008),(123,1478004033),(124,1478004058),(125,1478004084),(126,1478004109),(127,1478004135),(128,1478004161),(129,1478004187),(130,1478004214),(131,1478004241),(132,1478004269),(133,1478004296),(134,1478004324),(135,1478004353),(136,1478004381),(137,1478004410),(138,1478004439),(139,1478004469),(140,1478004498),(141,1478004528),(142,1478004558),(143,1478004589),(144,1478004619),(145,1478004651),(146,1478004682),(147,1478004714),(148,1478004746),(149,1478004778),(150,1478004811),(151,1478004844),(152,1478004877),(153,1478004911),(154,1478004945),(155,1478004979),(156,1478005014),(157,1478005049),(158,1478005084),(159,1478005120),(160,1478005156),(161,1478005193),(162,1478005231),(163,1478005268),(164,1478005306),(165,1478005344),(166,1478005383),(167,1478005422),(168,1478005461),(169,1478005501),(170,1478005541),(171,1478005582),(172,1478005622),(173,1478005663),(174,1478005704),(175,1478005746),(176,1478005788),(177,1478005831),(178,1478005873),(179,1478005917),(180,1478005960),(181,1478006004),(182,1478006049),(183,1478006094),(184,1478006139),(185,1478006186),(186,1478006231),(187,1478006277),(188,1478010694),(189,1478010747),(190,1478010799),(191,1478010835),(192,1478010862),(193,1478010884),(194,1478010904),(195,1478010924),(196,1478010942),(197,1478010961),(198,1478010980),(199,1478010999),(200,1478011018),(201,1478011037),(202,1478011056),(203,1478011075),(204,1478011094),(205,1478011113),(206,1478011132),(207,1478011151),(208,1478011170),(209,1478011189),(210,1478011208),(211,1478011227),(212,1478011246),(213,1478011265),(214,1478011285),(215,1478011304),(216,1478011324),(217,1478011344),(218,1478011363),(219,1478011383),(220,1478011403),(221,1478011423),(222,1478011443),(223,1478011464),(224,1478011485),(225,1478011506),(226,1478011528),(227,1478011549),(228,1478011571),(229,1478011593),(230,1478011616),(231,1478011638),(232,1478011662),(233,1478011685),(234,1478011708),(235,1478011732),(236,1478011757),(237,1478011782),(238,1478011807),(239,1478011832),(240,1478011858),(241,1478011885),(242,1478011912),(243,1478011939),(244,1478011967),(245,1478011996),(246,1478012025),(247,1478012054),(248,1478012086),(249,1478012115),(250,1478012146),(251,1478012178),(252,1478012210),(253,1478012244),(254,1478012277),(255,1478012312),(256,1478012347),(257,1478012382),(258,1478012419),(259,1478012456),(260,1478012494),(261,1478012531),(262,1478012570),(263,1478012609),(264,1478012649),(265,1478012689),(266,1478012730),(267,1478012771),(268,1478012813),(269,1478012855),(270,1478012898),(271,1478012941),(272,1478012984),(273,1478013028),(274,1478013072),(275,1478013117),(276,1478013163),(277,1478013209),(278,1478013255),(279,1478013302),(280,1478013350),(281,1478013399),(282,1478013449),(283,1478013500),(284,1478013551),(285,1478013604),(286,1478013658),(287,1478013714),(288,1478013771),(289,1478013830),(290,1478013891),(291,1478013954),(292,1478014019),(293,1478014086),(294,1478014156),(295,1478014228),(296,1478014301),(297,1478014373),(298,1478014446),(299,1478014518),(300,1478014591),(301,1478014664),(302,1478014736),(303,1478014809),(304,1478014882),(305,1478015377),(306,1478015422),(307,1478015480),(308,1478015543),(309,1478015608),(310,1478015676),(311,1478015740),(312,1478015803),(313,1478015864),(314,1478015921),(315,1478015977),(316,1478016030),(317,1478016081),(318,1478016129),(319,1478016176);
I assume you need to get the pulse count in n-minute (in your case 5 minutes) intervals. For achieving this, please try the following query SELECT COUNT(*) AS gas_pulse_count, FROM_UNIXTIME(pulse_time - MOD(pulse_time, 5 * 60)) from_time, FROM_UNIXTIME((pulse_time - MOD(pulse_time, 5 * 60)) + 5 * 60) to_time FROM gas_pulse GROUP BY from_time
Retrieve one out of every n records
I have a table containing thousands of records representing the temperature of a room in a certain moment. Up to now I have been rendering a client side graph of the temperature with JQuery. However, as the amount of records increases, I think it makes no sense to provide so much data to the view, if it is not going to be able to represent them all in a single graph. I would like to know if there exists a single MySQL query that returns one out of every n records in the table. If so, I think I could get a representative sample of the temperatures measured during a certain lapse of time. Any ideas? Thanks in advance. Edit: add table structure. CREATE TABLE IF NOT EXISTS `temperature` ( `nid` int(10) unsigned NOT NULL COMMENT 'Node identifier', `temperature` float unsigned NOT NULL COMMENT 'Temperature in Celsius degrees', `timestamp` int(10) unsigned NOT NULL COMMENT 'Unix timestamp of the temperature record', PRIMARY KEY (`nid`,`timestamp`) )
You could do this, where the subquery is your query, and you add a row number to it: SET #rows=0; SELECT * from( SELECT #rows:=#rows+1 AS rowNumber,nid,temperature,`timestamp` FROM temperature ) yourQuery WHERE MOD(rowNumber, 5)=0 The mod would choose every 5th row: The 5 here is your n. so 5th row, then 10th, 15th etc.
Not really sure what your asking but you have multiple options You can limit your results to n (n representing the amount of temperatures you want to display) just a simple query with the limit in the end: select * from tablename limit 1000 You could use a time/date restraint so you display only the results of the last n days. Here is an example that uses date functions. The following query selects all rows with a date_col value from within the last 30 days: mysql> SELECT something FROM tbl_name -> WHERE DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= date_col; You could select an average temperature of a certain period, the shorter the period the more results you'll get. You can group by date, yearweek, month etc. to "create the periods"
MySQL select records using MAX(datefield) minus three days
Clearly, I am missing the forest for the trees...I am missing something obvious here!
Scenario:
I've a typical table asset_locator with multiple fields:
id, int(11) PRIMARY
logref, int(11)
unitno, int(11)
tunits, int(11)
operator, varchar(24)
lineid, varchar(24)
uniqueid, varchar(64)
timestamp, timestamp
My current challenge is to SELECT records from this table based on a date range. More specifically, a date range using the MAX(timestamp) field.
So...when selecting I need to start with the latest timestamp value and go back 3 days.
EX: I select all records WHERE the lineid = 'xyz' and going back 3 days from the latest timestamp. Below is an actual example (of the dozens) I've been trying to run.
MySQL returns a single row with all NULL values for the following:
SELECT id, logref, unitno, tunits, operator, lineid,
uniqueid, timestamp, MAX( timestamp ) AS maxdate
FROM asset_locator
WHERE 'maxdate' < DATE_ADD('maxdate',INTERVAL -3 DAY)
ORDER BY uniqueid DESC
There MUST be something obvious I am missing. If anyone has any ideas, please share.
Many thanks!
MAX() is an aggregated function, which means your SELECT will always return one row containing the maximum value. Unless you use GROUP BY, but it looks that's not what you need.
http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_max
If you need all the entries between MAX(timestamp) and 3 days before, then you need to do a subselect to obtain the max date, and after that use it in the search condition. Like this:
SELECT id, logref, unitno, tunits, operator, lineid, uniqueid, timestamp
FROM asset_locator
WHERE timestamp >= DATE_ADD( (SELECT MAX(timestamp) FROM asset_locator), INTERVAL -3 DAY)
It will still run efficiently as long as you have an index defined on timestamp column.
Note: In your example
WHERE 'maxdate' < DATE_ADD('maxdate',INTERVAL -3 DAY)
Here you were are actually using the string "maxdate" because of the quotes causing the condition to return false. That's why you were seeing NULL for all fields.
Edit: Oops, forgot the "FROM asset_locator" in query. It got lost at some point when writing the answer :)
MySQL delete entries based on last two digits of Unix/Epoch time
I have a table with three columns: `id` int(11) NOT NULL auto_increment `tm` int NOT NULL `ip` varchar(16) NOT NULL DEFAULT '0.0.0.0' I want to run a query that will check if the same IP was logged within a minute and then delete all but one of those entries. For example I have the two rows below. id=1 tm=1361886629 ip=192.168.0.1 id=2 tm=1361886630 ip=192.168.0.1 I would only like to keep one in the database. I have read lots of other remove duplicate/partial duplicate entry questions but I'm looking for a way to compare the last two digits of the Unix/epoch time and delete all but one based on that plus the IP. Any help is much appreciated.
you can use CAST in mysql to remove the last 2 digits SELECT CAST( tm AS CHAR( 8 ) ) this will select only the first 8 digits from the timestamp and allow you to find duplicates if you only want to know what the last 2 digits are SELECT RIGHT(CAST( tm AS CHAR( 10 ) ), 2) this will select the last two digits only from each timestamp
Once an hour results from MySQL
Consider a table such as this: CREATE TABLE records ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, eventOccured DATETIME NOT NULL, eventType INT NOT NULL, eventDescription VARCHAR(32) ) I would like to retrieve the eventOccured and eventType fields from the entire table, but if two or more events occurred within an hour of each other then I would want only the first of them. This would be be simple if everything from N:00 to N:59 were considered the same hour, but in this case an event at 12:15 of eventType "5" would be considered to have occurred less than an hour after an 11:45 eventType "5", and so should not be returned. Can this be done in MySQL without a stored procedure? I could write such a procedure, but I worry that it will be rather resource-intensive and I would love to learn if MySQL has such ability out of the box.
What you are saying is that you want all events, where there is not another event in the next 60 minutes. This query does this in what should be a mysql friendly way: select * from records r where not exists (select 1 from records r2 where r2.eventOccured > r.eventOccured and timestampdiff(minute, r.eventOccured, r2.eventOccured) < 60 )