Apologies for the simple question I am new to using PostgreSQL and Psycopg2. I have two columns in a table I am trying to populate using values from two other tables based on a where conditional. Example code below:
cur = con.cursor()
db_insert = """INSERT INTO "Database"."TABLE_ONE"
("LT_ID_ONE", "LT_ID_TWO")
VALUES(
(SELECT "LT_ID_ONE" FROM "Database"."TABLE_TWO" WHERE "LT_NUM_ONE" =%s),
(SELECT "LT_ID_TWO" FROM "Database"."TABLE_THREE" WHERE "LT_NUM_TWO" =%s)
);"""
insert_values = (df1.iloc[0, 0], df1.iloc[0, 1])
cur.execute(db_insert, insert_values)
When running this command I receive the following error:
psycopg2.errors.NotNullViolation: null value in column "LOT_ID_ONE" violates not-null constraint
DETAIL: Failing row contains (null, null).
Any help would be appreciated.
Looks as though my error was in the order of the elements for the insert_values variable. Once I swapped them it worked. So the SQL code I have is correct.
Related
I am trying to delete some duplicate records from mysql table but it was not working.
I am taking help of https://www.javatpoint.com/mysql-delete-duplicate-records
If I will try with example database which is given example it was working fine.
But in my table it was not working.
DELETE S1 FROM employee_attendance AS S1 INNER JOIN employee_attendance AS S2 WHERE S1.DbKey < S2.DbKey AND S1.DivisionDbKey = S2.DivisionDbKey AND S1.Date = S2.Date AND S1.Month = S2.Month AND S1.FinancialYearDbKey = S2.FinancialYearDbKey AND S1.EmployeeDbKey = S2.EmployeeDbKey AND S1.Attendance = S2.Attendance AND S1.InTime = S2.InTime AND S1.OutTime = S2.OutTime AND S1.EmployeeDbKey = 6798 AND S1.Month = '05' AND S1.FinancialYearDbKey = 5;
I am getting error
#1205 - Lock wait timeout exceeded; try restarting transaction
I have tried with another example https://www.geeksforgeeks.org/sql-query-to-delete-duplicate-rows/
DELETE FROM employee_attendance WHERE DbKey NOT IN (SELECT MAX(DbKey) FROM employee_attendance WHERE EmployeeDbKey = 6798 AND Month = '05' AND FinancialYearDbKey = '5' GROUP BY DivisionDbKey,Date,Month,FinancialYearDbKey,EmployeeDbKey,Attendance,InTime,OutTime)
I am getting same error.
#1205 - Lock wait timeout exceeded; try restarting transaction
Any suggestion will be appriciated. Thank you.
I personally think this is a bad practice. You should instead make a (empty) duplicate of the table employee_attendance then define a UNIQUE KEY on that new table that will prevent duplicate entries.
Consider these steps:
Create a duplicate table:
CREATE TABLE employee_attendance_new LIKE employee_attendance;
Add UNIQUE INDEX - now, this is just a simple example. You can add or reduce columns to the unique index but make sure that you drop the existing unique index first then only you re-create:
ALTER TABLE employee_attendance_new
ADD UNIQUE INDEX unq_idx(EmployeeDbKey, date, InTime, OutTime);
Insert the data into the new table using INSERT IGNORE..:
INSERT IGNORE INTO employee_attendance_new
SELECT * FROM employee_attendance;
Check and compare both table. If you're satisfied with the result, rename those tables:
RENAME TABLE employee_attendance TO employee_attendance_old;
RENAME TABLE employee_attendance_new TO employee_attendance;
Now you have the new table with no duplicates and the old table for reference or in case there are some data you need from it.
Fiddle example
I need to merge some randomly uppercased data that has been collected in an SQLite table key_val, such that key is always lowercase and no vals are lost. There is a unique compound index on key,val.
The initial data looks like this:
key|val
abc|1
abc|5
aBc|1
aBc|5
aBc|3
aBc|2
AbC|1
abC|3
The result after the merge would be
key|val
abc|1
abc|2
abc|3
abc|5
In my programmer brain, I would
for each `key` with upper case letters;
if a lower cased `key` is found with the same value
then delete `key`
else update `key` to lower case
Re implementing the loop has a sub query for each row found with upper case letters, to check if the val already exists as a lower case key
If it does, I can delete the cased key.
From there I can UPDATE key = lower(key) as the "duplicates" have been removed.
The first cut of the programming method of finding the dupes is:
SELECT * FROM key_val as parent
WHERE parent.key != lower(parent.key)
AND 0 < (
SELECT count(s.val) FROM key_val as s
WHERE s.key = lower(parent.key) AND s.val = parent.val
)
ORDER BY parent.key DESC;
I'm assuming there's a better way to do this in SQLite? The ON CONFLICT functionality seems to me like it should be able to handle the dupe deletion on UPDATE but I'm not seeing it.
First delete all the duplicates:
DELETE FROM key_val AS k1
WHERE EXISTS (
SELECT 1
FROM key_val AS k2
WHERE LOWER(k2.key) = LOWER(k1.key) AND k2.val = k1.val AND k2.rowid < k1.rowid
);
by keeping only 1 combination of key and val with the min rowid.
It is not important if you kept the key with all lower chars or not, because the 2nd step is to update the table:
UPDATE key_val
SET key = LOWER(key);
See the demo.
Honestly it might just be easier to create a new table and then insert into it. As it seems you really just want a distinct select here, use:
INSERT INTO kev_val_new ("key", val)
SELECT DISTINCT LOWER("key"), val
FROM key_val;
Once you have populated the new table, you may drop the old one, and then rename the new one to the previous name:
DROP TABLE key_val;
ALTER TABLE key_val_new RENAME TO key_val;
I agree with #Tim that it would be easire to re-create table using simple select distict lower().. statement, but that's not always easy if table has dependant objects (indexes, triggers, views). In this case this can be done as sequence of two steps:
insert lowered keys which are not still there:
insert into t
select distinct lower(tr.key) as key, tr.val
from t as tr
left join t as ts on ts.key = lower(tr.key) and ts.val = tr.val
where ts.key is null;
now when we have all lowered keys - remove other keys:
delete from t where key <> lower(key);
See fiddle: http://sqlfiddle.com/#!5/84db50/11
However this method assumes that key is always populated (otherwise it would be a strange key)
If vals can be null then "ts.val = tr.val" should be replaced with more complex stuff like ifnull(ts.val, -1) = ifnull(tr.val, -1) where -1 is some unused value (can be different). If we can't assume any unused value like -1 then it should be more complex check for null / not null cases.
I have a problem to add a new column to a SQLITE table if this column is not already exist.
I have try with this code but i don’t know why it wont execute:
IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'mytable' AND COLUMN_NAME = 'mynewcolumn')
BEGIN
ALTER TABLE mytable ADD COLUMN mynewcolumn TEXT
END
I get an Exception error :
error: near "IF": syntax error
This is the solution i select :
1- I do PRAGMA table_info :
pragma table_info(MyTable)
This command gives all the informations about all the columns of the table. each row correspand to the information of a column.
This commande return an output table with 4 columns : cid, name, type, notnull, dft value, pk
2- I read all the rows from "PRAGMA table_info (MyTable)", and i compare the column "name" with the name of the column i want to check if exist.
3- If Column exist then i dont do anything
4- but if the column doen't exist then, here i add the column to my table using this commade :
ALTER TABLE MyTable ADD COLUMN NewColumn TEXT;
this is work for me, and do the job correctly.
To test whether a column exists, execute PRAGMA table_info and check if the column name appears in the result.
I have a table named CUSTOMER, with few columns. One of them is Customer_ID.
Initially Customer_ID column WILL NOT accept NULL values.
I've made some changes from code level, so that Customer_ID column will accept NULL values by default.
Now my requirement is that, I need to again make this column to accept NULL values.
For this I've added executing the below query:
ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL
I'm getting the following error:
ORA-01451 error, the column already allows null entries so
therefore cannot be modified
This is because already I've made the Customer_ID column to accept NULL values.
Is there a way to check if the column will accept NULL values before executing the above query...??
You can use the column NULLABLE in USER_TAB_COLUMNS. This tells you whether the column allows nulls using a binary Y/N flag.
If you wanted to put this in a script you could do something like:
declare
l_null user_tab_columns.nullable%type;
begin
select nullable into l_null
from user_tab_columns
where table_name = 'CUSTOMER'
and column_name = 'CUSTOMER_ID';
if l_null = 'N' then
execute immediate 'ALTER TABLE Customer
MODIFY (Customer_ID nvarchar2(20) NULL)';
end if;
end;
It's best not to use dynamic SQL in order to alter tables. Do it manually and be sure to double check everything first.
Or you can just ignore the error:
declare
already_null exception;
pragma exception_init (already_null , -01451);
begin
execute immediate 'alter table <TABLE> modify(<COLUMN> null)';
exception when already_null then null;
end;
/
You might encounter this error when you have previously provided a DEFAULT ON NULL value for the NOT NULL column.
If this is the case, to make the column nullable, you must also reset its default value to NULL when you modify its nullability constraint.
eg:
DEFINE table_name = your_table_name_here
DEFINE column_name = your_column_name_here;
ALTER TABLE &table_name
MODIFY (
&column_name
DEFAULT NULL
NULL
);
I did something like this, it worked fine.
Try to execute query, if any error occurs, catch SQLException.
try {
stmt.execute("ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL");
} catch (SQLException sqe) {
Logger("Column to be modified to NULL is already NULL : " + sqe);
}
Is this correct way of doing?
To modify the constraints of an existing table
for example... add not null constraint to a column.
Then follow the given steps:
1) Select the table in which you want to modify changes.
2) Click on Actions.. ---> select column ----> add.
3) Now give the column name, datatype, size, etc. and click ok.
4) You will see that the column is added to the table.
5) Now click on Edit button lying on the left side of Actions button.
6) Then you will get various table modifying options.
7) Select the column from the list.
8) Select the particular column in which you want to give not null.
9) Select Cannot be null from column properties.
10) That's it.
I want to create a table in a SQLite database only if doesn't exist already. Is there any way to do this? I don't want to drop the table if it exists, only create it if it doesn't.
From http://www.sqlite.org/lang_createtable.html:
CREATE TABLE IF NOT EXISTS some_table (id INTEGER PRIMARY KEY AUTOINCREMENT, ...);
Am going to try and add value to this very good question and to build on #BrittonKerin's question in one of the comments under #David Wolever's fantastic answer. Wanted to share here because I had the same challenge as #BrittonKerin and I got something working (i.e. just want to run a piece of code only IF the table doesn't exist).
# for completeness lets do the routine thing of connections and cursors
conn = sqlite3.connect(db_file, timeout=1000)
cursor = conn.cursor()
# get the count of tables with the name
tablename = 'KABOOM'
cursor.execute("SELECT count(name) FROM sqlite_master WHERE type='table' AND name=? ", (tablename, ))
print(cursor.fetchone()) # this SHOULD BE in a tuple containing count(name) integer.
# check if the db has existing table named KABOOM
# if the count is 1, then table exists
if cursor.fetchone()[0] ==1 :
print('Table exists. I can do my custom stuff here now.... ')
pass
else:
# then table doesn't exist.
custRET = myCustFunc(foo,bar) # replace this with your custom logic