12/7/2023 0 Comments Postgresql for loop cursor![]() SQL cursors are closed with the CLOSE statement, or by the end of the transaction. Like PL/pgSQL, SQL also has a MOVE statement that moves the cursor position without retrieving rows. There is also an SQL statement FETCH that is more powerful than its PL/pgSQL equivalent, in that it can fetch more than one row at a time. ASENSITIVE and INSENSITIVE are redundant in PostgreSQL and are there for SQL standard compatibility.WITH HOLDmakes a cursor that won't close on its own when a transaction is finished.SCROLL means that you can move the cursor position backwards to fetch the same rows several times.BINARY will fetch the results in the internal binary format, which may be useful if you want to read bytea columns and avoid the overhead of escaping them as strings.Here is a brief explanation of each choice: Read more MongoDB profiler and database performance problem diagnosis and identification The following is a simple example of PL/pgSQL code that makes use of a cursor: LANGUAGE plpgsql $$DECLARE and / CURSOR FOR SELECT table_schema, table_name FROM information_schema.tables, * declare and open * WHERE table_name LIKEs "old_%" AND table_schema = "mydata" text in the schema and names OPEN LOOP /* prevent SQL injection /* EXECUTE format('DROP TABLE%I.%I', v_schema, v_name) END LOOP /* get the next result row /* FETCH c INTO v_schema, v_name /* system variable FOUND is set by FETCH /* EXIT WHEN NOT FOUND /* prevent SQL injection /* Not required close the window end $ Another benefit of using a cursor is that you can run multiple SQL statements concurrently, which is typically not possible in a single database session. In procedural code on the client or in the database, cursors are especially helpful because they let you loop through the results of a query. A position within a result set is indicated by a cursor. A cursor, however, enables you to fetch the result rows one at a time. ![]() You receive the entire result set in one step when a regular query is executed. When a query is ready to be run, PostgreSQL makes a portal where the result rows can be fetched. ![]() We will also see the dangers involved and how to properly use WITH HOLD cursors in a PL/pgSQL procedure. This article describes how cursors and transactions interact and how WITH HOLD can work around their limitations. Feature article NPMD solutions play a key role in helping IT ops support increasingly complex technologies and services with network visibility, detection of performance issues and root cause analysisĬursors and transactions serve as the basic building blocks for creating database applications.The first of its kind, DPM provides decision support for each stage of the performance problem lifecycle DPM DPM is an innovative platform for IT production database performance management.If that isn't the case, you need to update your question to include more details on what you're trying to do with this procedure. In all three cases, I've assumed that you were trying to update the start_date column (and that it's of DATE datatype). Set start_date = to_date('31-12-4712', 'dd-mm-yyyy') - assuming start_date is of DATE datatype In your case, you didn't even need the cursor to loop through, since you're updating all the rows in tab_abc, so your update becomes simply: create or replace package body package_name However, far better and more performant is to use a single update statement to do the work in one fell swoop, rather than row-by-row. However, there's an easier way of looping through a cursor, where you don't have to worry about creating a variable to return values into, opening or closing the cursor or fetching the records - the cursor-for-loop will handle all this for you: create or replace package body package_name Into l_person_id, l_eff_start_date, l_eff_end_date Select person_id, eff_start_date, eff_end_date You have some options - first off, here is what your code should look like - you don't need that outer loop at all: create or replace package body package_name ![]() Your code isn't working as you expect because a) you are missing the exit clause from your outer loop, b) until you have fetched at least row, the %ROWCOUNT will return 0 (and even if it had fetched a row, if you're expecting it to return the number of rows in the cursor, then you're sadly mistaken - we'll only know the number of rows returned by the cursor once we've finished fetching all the rows from the cursor), c) with l_eff_start_date = '3' you are trying to set a variable as part of an update statement - this doesn't make sense! - and d) you haven't declared the l_person_id, l_eff_start_date, l_eff_end_date or num_count variables. ![]()
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