To use a PL/SQL cursor we set up a scenario where we want to update values from a main table and also add auditing data about it.
We create tables in oracle database to hold data about bookmarks and revision info data (bookmarks auditing table, and a revision info table):
- BOOKMARK - to hold data about bookmarks
- REVINFO - holds data about the revisions that took place in our system
- BOOKMARK_AUD - audit table, to hold data from the main table (BOOKMARK) that were affected by the different revisions
The concept from the scenarios is inspired from the Hibernate Envers project, where you would the same functionality
in java, automatically, with annotations. There might be cases where you need to this at the SQL level, maybe for
some single time house keeping jobs or similar...
CREATE TABLE bookmark ( id NUMBER(10, 0), -- number 10 digits before the decimal and 0 digits after the decimal title VARCHAR2(255 CHAR) NOT NULL, -- String with a maximum length of 255 charachters url VARCHAR2(500 CHAR) UNIQUE NOT NULL, -- holds unique values across the table data category VARCHAR2(500 CHAR) NOT NULL, -- holds unique values across the table data is_public NUMBER(1, 0) NOT NULL, -- plays the role of a boolean '0'-false, '1'-true , created_at DATE NOT NULL, -- when the entry is created PRIMARY KEY( id ) ); -- revision info table CREATE TABLE revinfo ( id NUMBER(10, 0) NOT NULL, revtstmp NUMBER(10, 0), -- unix time in milliseconds PRIMARY KEY( id ) ) -- audit table for BOOKMARK table CREATE TABLE bookmark_aud ( id NUMBER(10, 0), rev NUMBER(10, 0) NOT NULL, -- the id of the revision revtype NUMBER(1, 0), -- 0=CREATE, 1=MODIFY and 2=DELETE title VARCHAR2(255 CHAR) NOT NULL, url VARCHAR2(500 CHAR) UNIQUE NOT NULL, category VARCHAR2(500 CHAR) NOT NULL, is_public NUMBER(1, 0) NOT NULL, created_at DATE NOT NULL, PRIMARY KEY( id ) ); More exactly, we want to update all the entries from the bookmark table that have a given category (v_category in plsql code), with a new one (v_new_category in the plsql script). We select the values afect in a cursor (bookmark_cur in plsql script), which we iterate over in a plsql FOR LOOP to do the individual updates and inserts. If any exception occurs in the loop it will be printed in the DBMS_OUTPUT:
SET SERVEROUTPUT ON; DECLARE v_category VARCHAR2(500) := 'javax'; v_new_category VARCHAR2(500) := 'java'; next_rev_id NUMBER := HIBERNATE_SEQUENCE.nextval; created_at NUMBER(19, 0); CURSOR bookmark_cur IS SELECT * FROM bookmark WHERE category = v_category ); BEGIN -- get current timestamp as number SELECT EXTRACT(DAY FROM(sys_extract_utc(systimestamp) - to_timestamp('1970-01-01', 'YYYY-MM-DD'))) * 86400000 + to_number(TO_CHAR(sys_extract_utc(systimestamp), 'SSSSSFF3')) INTO created_at FROM dual; -- update REVISION table INSERT INTO revinfo ( rev, revtstmp ) VALUES ( next_rev_id, created_at ); FOR c IN bookmark_cur LOOP BEGIN -- update BOOKMARK table UPDATE bookmark SET category = v_new_category WHERE id = c.id; -- INSERT ENTRY into BOOKMARK_AUD table INSERT INTO bookmark_aud ( id title, url, category, is_public, created_at, rev, revtype ) VALUES ( c.id c.title, c.url, c.category, c.is_public, c. created_at, next_rev_id, 1 -- 1=UPDATE/MODIFY (0=INSERT and 2=DELETE) ); EXCEPTION WHEN OTHERS THEN --handle all exceptions DBMS_OUTPUT.PUT_LINE('Exception' || SQLCODE || ' captured for bookmark with id ' || c.id); END; END LOOP; END; / But beware, it is not recommended using a cursor FOR loop if the body executes non-query DML (INSERT, UPDATE, DELETE, MERGE),
because the INSERT or UPDATE will happen on a row-by-row basis1.
In this particular case you can ditch the cursor and use use plain SQL updates and inserts in the plsql body, as shown
in the snippet below:
BEGIN -- get current timestamp as number SELECT EXTRACT(DAY FROM(sys_extract_utc(systimestamp) - to_timestamp('1970-01-01', 'YYYY-MM-DD'))) * 86400000 + to_number(TO_CHAR(sys_extract_utc(systimestamp), 'SSSSSFF3')) INTO created_at FROM dual; -- update REVISION table INSERT INTO revinfo ( rev, revtstmp ) VALUES ( next_rev_id, created_at ); -- update BOOKMARK table UPDATE bookmark SET category = v_new_category WHERE category = v_category; -- -- INSERT ENTRY into BOOKMARK_AUD table INSERT INTO bookmark_aud ( id title, url, category, is_public, created_at, rev, revtype ) SELECT c.id c.title, c.url, c.category, c.is_public, c. created_at, next_rev_id, 1 -- 1=UPDATE/MODIFY (0=INSERT and 2=DELETE) FROM bookmark c WHERE c.id in ( SELECT id FROM bookmark WHERE category = v_category ) ); EXCEPTION WHEN OTHERS THEN --handle all exceptions DBMS_OUTPUT.PUT_LINE('Exception' || SQLCODE || ' captured for bookmark with id ' || c.id); END; / Note some times is not possible and then you might have to stick to the cursor. In oracle you can take advantage
of the CURSOR bulk updates and INSERTS2
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