![]() Solution for our example scenarioįirst, we need to re-create the table with the present address column as: DROP TABLE IF EXISTS ALL_EMPLOYEES On the other hand, the can be either the DO NOTHING or the DO UPDATE statement. The target can be either a column name or a constraint name or a WHERE clause. To take the benefit of this feature, we need to use the INSERT ON CONFLICT syntax which is like: UPSERT is basically INSERT+UPDATE, i.e., it says that if no similar record is found, then you may insert the record, otherwise update the matching existing record with the information provided. So here the insert should be conditional. In such case, we cannot simply run an INSERT query because that would create multiple employee ids for the same employee requesting an address update. ![]() Now this batch contains both new employees joining the company and also employees requesting for a change in their postal address. Assume that we get a batch of employees every day whose details need to be entered into this table. Well, now suppose we have this ALL_EMPLOYEES table containing the present address of employees, too. ![]() The record set in the ALL_EMPLOYEES table looks like: It shows the names which have been removed from the ALL_EMPLOYEES table. RETURNING ALL_EMPLOYEES.FIRST_NAME || ' ' || ALL_EMPLOYEES.LAST_NAME WHERE SEP_EMPLOYEES.EMPLOYEE_ID = ALL_EMPLOYEES.EMPLOYEE_ID So now when we need to remove the data of SEP_EMPLOYEES from ALL_EMPLOYEES, we can write: DELETE FROM ALL_EMPLOYEES INSERT INTO ALL_EMPLOYEES (first_name, last_name, department) VALUES ('David', 'Willson', 'DBA') INSERT INTO ALL_EMPLOYEES (first_name, last_name, department) VALUES ('Stephen', 'Johnas', 'Senior Dev') Now let's feed some dummy data into these tables as: INSERT INTO ALL_EMPLOYEES (first_name, last_name, department) VALUES ('Sabyasachi', 'Mukherjee', 'IT Analyst') First we need to create the tables as: DROP TABLE IF EXISTS ALL_EMPLOYEES To solve our problem we discussed, we need to use this DELETE with USING. In the WHERE clause, use the columns from the tables in the USING clause to join the data (equivalent to join condition).After the USING clause, specify the table expression, which can be one or even more tables (equivalent to join).But we can use the USING clause with the DELETE statement to have the same functionality achieved. PostgreSQL does not support the DELETE JOIN statement. ![]() In this case, we need to do a conditional delete from the ALL_EMPLOYEES table. Now, the company wants to clean up their database of all the separated employees' information from the ALL_EMPLOYEES table. Suppose we also have a table, called SEP_EMPLOYEES, which contains those employees' information who have separated from the company. Suppose we have a table, called ALL_EMPLOYEES, which contains all employees' information who are working or had ever worked for the company. But we sometimes get confused when we need to insert or delete records conditionally from a table. INSERT INTO foo ( bar ) VALUES ( 'test 2' )Ĭlearly, this can't know if there's a conflict without incrementing the sequence, so the "do nothing" has to come after that increment.We are comfortable with inserting/deleting record(s) into/from a table. SELECT setval(pg_get_serial_sequence('foo', 'id'), 0, true) INSERT INTO foo ( bar ) VALUES ( 'test' ) This can be seen intuitively if the duplicate key is in the autoincrement field itself: CREATE TABLE foo ( id SERIAL NOT NULL PRIMARY KEY, bar text ) Resolve default values, including incrementing the sequence.Before the DBMS can do anything with the data, it's got to have a complete set of columns, so the order of operations is like this: A SERIAL column in Postgres is implemented as a DEFAULT which executes the nextval() function on a bound SEQUENCE. Check values to insert against constraintīut in fact, the increment has to happen before the insert is attempted.The reason this feels weird to you is that you are thinking of the increment on the counter as part of the insert operation, and therefore the "DO NOTHING" ought to mean "don't increment anything".
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