9/5/2023 0 Comments Postgresql for loop cursor![]() ![]() In the previous example, the rental_cursor cursor will return rows that each contain three columns. Next, I can FETCH into a comma-separated list of variables. rental.customer_id, and rental.rental_date When you FETCH into a variable of some %ROWTYPE, you can refer to the individual columns using the usual variable. Let's look at each of these destination types in more detail. Three variables: one of type rentals.tape_id%TYPE, one of type rentals.customer_id%TYPE, and the last of type rentals.rental_date%TYPE For example, if the cursor SELECTs a row from the rentals table, there are three possible destinations: The destination (or destination s) must match the shape of a row returned by the cursor. The syntax for the FETCH statement isįETCH cursor-name INTO destination ] When you fetch a row from a cursor, you have to provide one or more destination variables that PL/pgSQL can stuff the results into. FETCHĪfter a bound cursor has been opened, you can retrieve the result set (one row at a time) using the FETCH statement. You can repeat the OPEN, FETCH, CLOSE cycle if you want to process the cursor results again. When you use a cursor, you first DECLARE it, then OPEN it, FETCH from it, and finally CLOSE it, in that order. If you try to FETCH (see the section that follows) from a cursor that has not been opened, you'll receive an error message ( cursor " name " is invalid). If you try to OPEN a cursor that is already open, you will receive an error message ( cursor " name " already in use). ![]() The cursor variable is said to be bound to this query, and the variable is a bound cursor variable.īefore you can use a bound cursor, you must open the cursor using the OPEN statement: When you declare a variable of type CURSOR, you must include a query. Rental_cursor is declared to be a cursor for the result set of the query SELECT * FROM rentals. Rental_cursor CURSOR FOR SELECT * FROM rentals The following code snippet shows how you might declare a cursor variable: You must declare a cursor variable just as you declare any other variable. You can think of a cursor as a name for a result set. Processing a result set using a cursor is similar to processing a result set using a FOR loop, but cursors offer a few distinct advantages that you'll see in a moment. I will turn the columns into arrays and feed them into the function and try using query parallelism, too.Direct cursor support is new in PL/pgSQL version 7.2. (partition by loggerid order by loggerid, datecon, timecon)) as distance_interval ST_Distance(gcs_geom::geography, lag(gcs_geom::geography) over Lag(datecon + timecon) over (partition by loggerid order by loggerid, datecon, timecon) as prev_datetime, Time_interval_seconds = (extract(EPOCH from (datecon + timecon) - subquery.prev_datetime)),Ĭalculated_speed = subquery.distance_interval/(extract(EPOCH from (datecon + timecon) - subquery.prev_datetime)) Set time_interval = (datecon + timecon) - subquery.prev_datetime,ĭistance_interval = subquery.distance_interval, When t_row.after_bat_off = 1 or t_row.first_point = 1 Select "id", loggerid, datecon, timecon, gcs_geom, after_bat_off, first_point from mytable create or replace function speed_cal_cutoff() How can I optimize the code for better performance?Ĭombining all UPDATEs into one and then DELETE on table with 10k records reduces the execution time by 2 minutes. Set calculated_speed = gcs_distance/interval_secondsĭelete from mytable where calculated_speed > 41.6667 ![]() Set interval_seconds = (extract(EPOCH from time_interval)) Lag(loggerid) over (partition by loggerid order by datecon, timecon) as prev_loggerid Lag(concat(datecon|| ' ' ||timecon)::timestamp) over (partition by loggerid order by loggerid, datecon, timecon) as prev_datetimeĪnd mytable.loggerid = subquery.prev_loggeridįrom (select "id", ST_Distance(gcs_geom::geography, lag(gcs_geom::geography) over (partition by loggerid order by loggerid, datecon, timecon asc)) as gcs_distance, Lag(loggerid) over (partition by loggerid order by datecon, timecon) as prev_loggerid, Set time_interval = (concat(datecon|| ' ' ||timecon)::timestamp) - prev_datetime Interval_seconds, calculated_speed from mytable Indexes, work_mem, fillfactor and vacuum full do not make significant changes. The sample table has around 500k records, but takes hours to execute and still do not finish. I am creating a for-loop function to update multiple columns (time, distance and speed) calculated from values of the current row and previous row, and delete the row whose value from the updated column (speed) exceeds the cutoff value. ![]()
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