![]() ![]() You can view EDUCBA’s recommended articles for more information. We hope that this EDUCBA information on “Cursors in PostgreSQL” was beneficial to you. If we read data from the cursor, other sessions can do their operations without impacting other connections. As alluded to in earlier threads, this is done by converting such cursors to holdable. It is used to save memory and network bandwidth on the server. Here is a patch that allows COMMIT inside cursor loops in PL/pgSQL. Use the more convenient implicit cursor of a FOR loop: CREATE OR REPLACE FUNCTION testloop(). It is essential in PostgreSQL to fetch single records from the complete result set. But typically, you dont need an explicit cursor to loop. While holding a row, other processes can update, select or delete the rows. If we are doing operations on the table, it will not affect the cursor directly.The cursor minimizes the load on the server as well as our network bandwidth. ![]() This cursor saves memory because the client and server do not need more memory to store the data results.This cursor will save time because we don’t need to wait to retrieve or process the whole data set.The main importance of the cursor in PostgreSQL retrieves a single record from the result set.Left join customer cust on emp.emp_id = cust.cust_id We have used the employee and customer tables to join the table.Įxample CREATE OR REPLACE FUNCTION testing_trigger()Ĭur CURSOR FOR select * from employee emp.Below is an example of creating a cursor using the function in PostgreSQL.Example: OPEN c FOR SELECT id FROM a WHERE ok LOOP UPDATE b SET aok TRUE WHERE aid c.id END LOOP Use a FOR r IN SELECT. I switched from %I to %s, because the regclass parameter is automatically properly escaped when (automatically) converted to text.Create or replace function (function name)ĭECLARE cursor_name (Any name given to cursor) ĬURSOR (keyword) for query (query to use in cursor) Use an explicit cursor in PL/pgSQL and loop through it and process each result row. or go with the more elegant approach of using a regclass type:ĬREATE OR REPLACE FUNCTION f_nocurs(_tbl regclass)ĮXECUTE format('UPDATE %s SET tbl_id = tbl_id + 1000', _tbl).either pass and escape them separately,.Answer for (ii)Ī schema-qualified table name like trace.myname actually consists of two identifiers. Or better, yet (if possible!): Rethink your problem in terms of set-based operations and execute a single (dynamic) SQL command: - Set-base dynamic SQLĬREATE OR REPLACE FUNCTION f_nocurs(_tbl text)ĮXECUTE format('UPDATE %I SET tbl_id = tbl_id + 1000', _tbl) Use the implicit cursor of a FOR loop instead: CREATE OR REPLACE FUNCTION f_curs2(_tbl text)įOR _ctid IN EXECUTE 'SELECT ctid FROM ' || quote_ident(_tbl) FOR UPDATEĮXECUTE format('UPDATE %I SET tbl_id = tbl_id + 100 WHERE ctid = $1', _tbl) Introduction to PL/pgSQL continue statement The continue statement prematurely skips the current iteration of the loop and jumps to the next one. There is normally no need for explicit cursors in plpgsql. Summary: in this tutorial, you will learn how to use the PL/pgSQL continue statement to control the loop. There is also a variant of the FOR statement to loop through cursors, but it only works for bound cursors. OPEN _curs FOR EXECUTE 'SELECT * FROM ' || quote_ident(_tbl) FOR UPDATE ĮXECUTE format('UPDATE %I SET tbl_id = tbl_id + 10 WHERE ctid = $1', _tbl) ![]() CREATE OR REPLACE FUNCTION f_curs1(_tbl text) Note that ctid is only guaranteed to be stable within the same transaction. I use the system column ctid instead to determine the row without knowing the name of a unique column. Hence, you cannot use the special syntax WHERE CURRENT OF cursor. Cursors are not visible inside the command. Explicit (unbound) cursorĮXECUTE is not a "clause", but a PL/pgSQL command to execute SQL strings. ![]()
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