OFFSET 100page FETCH NEXT 100 ROWS ONLY sqlcontinue CURSOR (sec int. Loop raise notice '% - %', rec.release_year, rec. CREATE & INSERT statements to create the PostgreSQL example database for Chapter. Query := query || 'order by release_year' Įlse raise 'invalid sort type %s', sort_type Query := 'select title, release_year from film ' do $$ declare - sort by 1: title, 2: release year This anonymous block composes the query based on the sort_type variable and uses the for loop to iterate over the row of the result set. We’ll use it in the using clause of the for loop. rec_count: is the number of rows to query from the film table.sort_type: 1 to sort the films by title, 2 to sort the films by release year.One basic property of a PostgreSQL cursor is that it only exists for the duration of a database transaction. The following block shows how to use the for loop statement to loop through a dynamic query. However, we have to use a cursor in our case, since we need to execute a dynamic SQL statement inside the loop. The using clause is used to pass parameters to the query.The query_expression is an SQL statement.The following form of the for loop statement allows you to execute a dynamic query and iterate over its result set: įor row in execute query_expression ] NOTICE: Worst Banger(185 mins) Code language: Shell Session ( shell ) Using PL/pgSQL for loop to iterate over the result set of a dynamic query One of the main factors to consider when choosing between a cursor and a loop is the performance impact on the database server. I am new to postgresql, and get a problem about nested loop.Here is my code: CREATE TABLE q39442172 ( id character varying, eventid character varying, createdat character varying ) in. $$ Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) NOTICE: Chicago North(185 mins) Limit 10 loop raise notice '%(% mins)', f.title, f.length The following statement uses the for loop to display the titles of the top 10 longest films. The following statement shows how to use the for loop statement to iterate over a result set of a query: NOTICE: Counter 5 Code language: Shell Session ( shell ) Using PL/pgSQL for loop to iterate over a result set It adds 2 to the counter after each iteration: do $$ begin for counter in 1.6 by 2 loop raise notice 'counter: %', counter The following example uses the for loop statement to iterate over six numbers from 1 to 6. NOTICE: Counter: 1 Code language: Shell Session ( shell ) The following example iterates over 5 numbers from 5 to 1 and shows each number in each iteration: do $$ begin for counter in reverse 5.1 loop raise notice 'counter: %', counter NOTICE: Counter: 5 Code language: Shell Session ( shell ) The following example uses the for loop statement to iterate over five numbers from 1 to 5 and display each of them in each iteration: do $$ begin for counter in 1.5 loop raise notice 'counter: %', counter Įnd $$ Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) The following flowchart illustrates the for loop statement: The query must be a SELECT, or something else that returns rows (such as EXPLAIN ). The cursor cannot be open already, and it must have been declared as an unbound cursor variable (that is, as a simple refcursor variable). The for loop evaluates this step expression once only. The cursor variable is opened and given the specified query to execute.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |