I have 2 tables tbl_A and tbl_A_temp. Both the table have the same schema. their primary key differ since they are identity columns. Is there a way i can compare the two rows in these two table and get to know if they differ.I will be inserting data from tbl_A_temp to tbl_A, i need this compare just to make sure that I am not inserting any duplicate data in the main tables.
Regards,
Amit
I think this should work for you. Basically, since you don't have a primary key to join on, you'll need to perform a LEFT JOIN on all your other fields. If any are different, then the NULL check will be true:
SELECT t.*
FROM tbl_A_temp t
LEFT JOIN tbl_A a ON
t.field1=a.field1 AND t.field2=a.field2 AND ...
WHERE a.field1 IS NULL
I've also seen others use CHECKSUM, but have run into issues myself with it returning false positives.
Related
Prolog:
I have two tables in two different databases, one is an updated version of the other. For example we could imagine that one year ago I duplicated table 1 in the new db (say, table 2), and from then I started working on table 2 never updating table 1.
I would like to compare the two tables, to get the differences that have grown in this period of time (the tables has preserved the structure, so that comparison has meaning)
My way of proceeding was to create a third table, in which I would like to copy both table 1 and table 2, and then count the number of repetitions of every entry.
In my opinion, this, added to a new attribute that specifies for every entry the table where he cames from would do the job.
Problem:
Copying the two tables into the third table I get the (obvious) error to have two duplicate key values in a unique or primary key costraint.
How could I bypass the error or how could do the same job better? Any idea is appreciated
Something like this should do what you want if A and B have the same structure, otherwise just select and rename the columns you want to confront....
SELECT
*
FROM
B
WHERE NOT EXISTS (SELECT * FROM A)
if NOT EXISTS doesn't work in your DBMS you could also use a left outer join comparing the rows columns values.
SELECT
A.*
from
A left outer join B
on A.col = B.col and ....
Is there anyway to cross tables with 2 keys, in case the first one doesn't exist?
For example:
I have a LEFT table called order that contains a field called key_1 and a RIGHT table called pre_order where key_1 is the primary key. The thing is: due to systemic errors, not all registers from order contain a key_1 value, even though they should. So, when left joining those tables, some data from my pre_order table will be missing.
If key_1 is empty in the order table, I'd like it to cross with a different key. In this case, a CONCAT of multiple fields that are common to both tables, that would garantee an artificial primary key.
I thought about using COALESCE, but in a first glance, it wouldn't work.
The logic is:
IF key_1 is not null nor empty, cross both tables with key_1
ELSE, cross it with a CONCAT of multiple common fields of both tables.
Unfortunately, it looks like the ON statement doesn't let me work freely around logic statements.
You can use case statement in on clause as below
On 1=case when isnull(table1.key_1,'')<>'' and isnull(table2.key_1)<>'' and table1.key_1 =table2.key_1 then 1
When (isnull(table1.key_1,'')<>'' or isnull(table2.key_1)<>'') and concat(table1.column1,column2)=concat(table.2.column1,column2) then 1 end
I have a table in Oracle of which one of the columns (named CONTENTSTRING) is a CLOB. However, some of the rows in this table have identical data in this column. What I'd like to do is remove all the rows except for one that have this identical data. How can I accomplish this?
Googling around, I see a ton of examples for comparing two columns. I also see examples comparing between two different tables. What I don't see is an example using one table and just comparing the rows! I do think I might need to use this function: dbms_lob.compare. However, I'm still not sure how I can set this function up.
From a programmer's perspective, I would think maybe I should do something like:
SELECT CONTENTSTRING FROM TABLE_ALPHA A
and then somehow do another select from the same table as TABLE_ALPHA B, and then use dmbs_lob.compare to compare the two columns. If the row numbers are different AND the column contents are equal, then the row from TABLE_ALPHA B can be deleted.
I think that's the right approach, but how exactly would I write this out in Oracle using SQL? I would appreciate any help or resources on this. Thanks!
DELETE
FROM TABLE_ALPHA A
WHERE EXISTS (
SELECT 1 FROM TABLE_ALPHA B
WHERE DBMS_LOB.COMPARE(A.CONTENTSTRING, B.CONTENTSTRING) = 0
AND A.ROWID > B.ROWID
)
This deletes all dublicates except first one.
This answer assumes that you have a primary key field in the source table (I called it id).
You can use a subquery to list the ids of the duplicated records : this works by self-joining the table with dbms_lob.compare and a comparison clause on the id. If duplicate rows exist with the same CLOB content, all ids but the most ancient (ie the smallest) are selected. The outer query just deletes the selected ids. The NVL will consider NULL contents as duplicates (if that's not relevant for your use case, just remove them).
DELETE FROM TABLE_ALPHA
WHERE id IN (
SELECT b.id
FROM TABLE_ALPHA a
INNER JOIN TABLE_ALPHA b
ON
(
(a.contentString IS NULL AND b.contentString IS NULL)
OR dbms_lob.compare(a.CONTENTSTRING, b.CONTENTSTRING) = 0
)
AND b.id > a.id
);
See this db fiddle.
If I join two tables together with left join and one of the tables is completely empty, I get a bunch of empty columns in the joined table.
Here is a fiddle demonstrating what I mean.
I would like the resulting joined table to not contain all those null columns
The number of columns that a query returns is fixed. It cannot change depending on whether a table is empty or not. So the answer is nope.
I want to get the results of a left join between two tables, with both having a column of the same name, the column on which I join. The following query is seen as valid by the import/export wizard in SQL Server, but it always gives an error. I have some more conditions, so the size wouldn't be too much. We're using SQL Server 2000 iirc and since we're using an externally developed program to interact with the database (except for some information we can't retrieve that way), we can not simply change the column name.
SELECT table1.*, table2.*
FROM table1
LEFT JOIN table2 ON table1.samename = table2.samename
At least, I think the column name is the problem, or am I doing something else wrong?
Do more columns than just your join key have the same name? If only your join key has the same name then simply select one of them since the values will be equivalent except for the non-matching rows (which will be NULL). You will have to enumerate all your other columns from one of the tables though.
SELECT table2.samename,table1.othercolumns,table2.*
FROM table1
LEFT JOIN table2 ON table1.samename = table2.samename
You may need to explicitly list the columns from one of the tables (the one with less fields), and leave out the 2nd instance of what would be the duplicate field..
select Table1.*, {skip the field Table2.sameName} Table2.fld2, Table2.Fld3, Table2.Fld4... from
Since its a common column, it APPEARS its trying to create twice in the result set, thus choking your process.
Since you should never use select *, simply replace it with the column names of the columns you want. THe join column has the same value (or null) in both sides of the join, so only select one of themm the one from table1 which will always have the value.
If you want to select all the columns from both tables just use Select * instead of including the tables separately. That will however leave you with duplicate column names in the result set, so even reading them out by name will not work and reading them by index will give inconsistent results, as changing the columns in the database will change the resultset, breaking any code depending on the ordinals of the columns.
Unfortunately the best solution is to specify exactly the columns you need and create aliases for the duplicates so they are unique.
I quickly get the column headings by setting the query to text mode and copying the top row ...