Python3 SQLite3-如果值为null则不插入

Question

I'm using Python3.6 and sqlite3

How can I insert values to the database only if they are not null? I have tested the database by inserting 200 duplicated rows just for sure that INSERT OR IGNORE works good and after that I get 200 rows all filled by the NULL.

My INSERT code is:

cursor.execute("""INSERT OR IGNORE INTO mytable (
    column1,
    column2,
    column3,
    column4,     /* INT, PRIMARY KEY, UNIQUE
    column5,
    column6) 
VALUES (?,?,?,?,?,?)""",
(
    value1,
    value2,
    value3,
    value4,
    value5,
    value6))
conn.commit()

How to fix that?

Now, when I'm writing this, I think it's maybe becouse my PRIMARY KEY column is not the first one? Could it be true?

Answer 1

INSERT OR IGNORE is saying to do the insert BUT to ignore conflicts (don't do them). A conflict occurs when a CONSTRAINT is breached/not obeyed.

It would appear that you have few CONSTRAINTS and at a guess only implicit CONSTRAINTS. That is if you have column4 INTEGER PRIMARY KEY or the same with AUTOINCREMENT then the implicit CONSTRAINTS,2 of them, are UNIQUE NOT NULL. However such a column, an alias of the rowid , is special and specifying NULL results in the column being assigned an integer that is unique within the table (ie it uniquely identifies the row).

PS The column position makes no difference.

So going back to the guess none of the columns have a specific CONSTRAINT coded so the ignore won't be triggered as there will be no CONFLICT as there are no CONSTRAINTS.

What you should do is for every column that you don't want NULL to be a valid value is to change the column definition to include NOT NULL in the column definition (after the column name and the column type).

So instead of (as an example) of having :-

CREATE TABLE mytable (
    column1 TEXT,
    column2 TEXT,
    column3 TEXT,
    column4 INTEGER PRIMARY KEY,
    column5 TEXT,
    column6 TEXT
);

You would have :-

CREATE TABLE mytable (
    column1 TEXT NOT NULL,
    column2 TEXT NOT NULL,
    column3 TEXT NOT NULL,
    column4 INTEGER PRIMARY KEY,
    column5 TEXT NOT NULL,
    column6 TEXT NOT NULL
);

Thus using the above table along with the following SQL :-

-- NOTE column4 omitted from list of columns thus null
INSERT OR IGNORE INTO mytable (column1,column2,column3,column5,column6) VALUES
    (1,2,3,4,5),        -- Will be inserted as no conflict
    (6,7,null,null,10), -- conflict so ignored
    (11,12,13,14,15),  -- no conflict
    (null,17,18,19,20), -- conflict
    (21,22,23,24,25), -- no conflict
    (26,null,28,29,230) -- conflict
;

Only 3 rows will be inserted as per and no nulls even though attempts were made to insert nulls:-

Whilst if the table were defined according to the first CREATE SQL above, the result of the INSERT SQL would have been :-