Update multiple columns on conflict postgres

问题

I have to write a query to update a record if it exists else insert it. I am doing this update/insert into a postgres DB. I have looked into the upsert examples and most of them use maximum of two fields to update. However, I want to update multiple columns. Example:

query="""INSERT INTO table (col1,col2,col3,col4,col5,col6,col7,col8,col9,..col20) VALUES(%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)
ON CONFLICT(col2) DO UPDATE SET (col1,col2,col3,col4,col5,col6,col7,col8,col9,..col20) VALUES(%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)"""

In the query above assume that col2 is a unique key, I am inserting and updating the same number of columns. I have to execute this query using pymysql(python library). In a simple insert statement, I know how to pass the tuple containing the parameters dynamically.

cursor.execute(insert_query, data_tuple)

But in this case, I have both places(insert and update) input to be dynamic. Considering the above upsert query, the way I pass the parameters to the cursor

cursor.execute(upsert_query,data_tuple,data_tuple)

However, this one throws up an error with the number of arguments being in the execute function. So how do I pass? Moreover, I am trying to use this way to pass parameters because using the assignment(=) would be a laborious thing to do for 20 columns.

Is there any other alternative way to do this? Like a simple "replace into" statement in mysql.

回答1:

The direct answer to your question is, you do a tuple + tuple to double the tuple.

cursor.execute(upsert_query, data_tuple + data_tuple)

Other Options:

If you have individual values and you are constructing the tuple, you can directly construct a tuple with twice the number of values.

query="""INSERT INTO table (col1,col2,col3,col4,col5,col6,col7,col8,col9,..col20) VALUES(%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)
ON CONFLICT(col2) DO UPDATE SET col1=%s, col3=%s, col4=%s, ..."""

cur.execute(query, (c1, c2, c3, ... c20, c1, c3, c4, ... c20))

You will have to specify the values (except col2) twice.

If you already have the tuple, which is what you originally asked, then you will use a + to merge the same tuple twice.

If you have the individual values and not the tuple, you could also use named parameters like a dictionary.

query="""INSERT INTO table (col1,col2,col3,col4...) VALUES(%(c1)s, %(c2)s, %(c3)s, %(c4)s...) ON CONFLICT(col2) DO UPDATE SET col1=%(c1)s, col3=%(c3)s, col4=%(c4)s, ..."""
cur.execute(query, {'c1': c1val, 'c2': c2val, 'c3': c3val, 'c4': c4val, ...})

This form is good for readability, passes parameters only once, and is easy to maintain (increase in columns, etc) if the number of columns change in the future.

回答2:

EDIT 2

So, after few exchanges : your problem seems to be how to use the cursor.execute function in pymysql. This is the link for the appropriate documentation : https://pymysql.readthedocs.io/en/latest/modules/cursors.html

I never code in python but the documentation seems quite precise on the execute method usage :

execute(query, args=None)

Execute a query
Parameters: 

    query (str) – Query to execute.
    args (tuple, list or dict) – parameters used with query. (optional)

Returns:    

Number of affected rows
Return type:    

int

If args is a list or tuple, %s can be used as a placeholder in the query. If args is a dict, %(name)s can be used as a placeholder in the query.

So maybe with a 'dict' type it is possible, but I do not think it is the philosophy of it.

Original post

I am quite not sure of what exactly you want to say by 'both places input to be dynamic', so I will put down some SQL here an do not hesitate if you have any question after :)

First a small initialization

CREATE TABLE test 
( 
    id int,
    value_1 varchar,
    value_2 bit
);

ALTER TABLE test
ADD CONSTRAINT ck_test UNIQUE(id, value_1, value_2);


INSERT INTO test
VALUES
    (1, 'test', cast(1 as bit))
    , (2, 'test_2', cast(0 as bit));

Second the error

INSERT INTO test
VALUES
    (1, 'test', cast(1 as bit));

Third the UPSERT

INSERT INTO test
VALUES 
    (1, 'test', cast(1 as bit))
ON CONFLICT ON CONSTRAINT ck_test
DO
    UPDATE 
        SETid = 3, value_1 = 'error';

Is that answering your question? Or is it more a string building problem?

EDIT So, I am not fond of alternative languages so I will put this in plpgsql:

do language plpgsql $$
declare 
    query varchar;
    id_insert int;
    value_1_insert varchar;
    value_2_insert bit;
    id_update int;
    value_1_update varchar;
    value_2_update bit;
begin
    id_insert := 4;
    value_1_insert := 'test';
    value_2_insert := cast(1 as bit);

    id_update := id_insert;
    value_1_update := 'error';
    value_2_update := cast(0 as bit);

    query := 'INSERT INTO test
                VALUES 
                    (
                        cast('||id_insert||' as int)
                        , '''||value_1_insert||'''
                        , cast('||value_2_insert||' as bit)
                    )
                ON CONFLICT ON CONSTRAINT ck_test
                DO
                    UPDATE 
                        SET 
                            id = cast('||id_update||' as int)
                            , value_1 = '''||value_1_update||'''
                            , value_2 =  cast('||value_2_update||' as bit);';
    execute query;
end;
$$;

Hope this helps ;)

来源：https://stackoverflow.com/questions/55922003/update-multiple-columns-on-conflict-postgres

标签

postgresql

sql-insert

pymysql

upsert

on-duplicate-key