I have a database full of simple note data, with columns for title, due date, priority, and details. There is also a _id column PRIMARY KEY int.
Say I have a note in the table already with some data filled and the rest null. I also have a set of data that will fill all those fields.
Is there a way that I can only write data to the fields that are NULL?
I can't overwrite existing data, but I'd like to add data to NULL columns.
I know the rowId of the target row.
If my target row had rowId of 5, I could do something like this:
UPDATE SET duedate='some date', priority='2', details='some text' WHERE _id=5
But that would overwrite all the data in that row, and I don't want to lose any data that might be there. How can I change this statement to avoid writing to non-null fields?
Suppose you start with
CREATE TABLE "t" ("a" , "b" , "c" );
INSERT INTO "t" ("a", "c") VALUES (1, 3);
Then
update t set a = coalesce(a,9), b = coalesce(b,10), c = coalesce(c,11);
Will update only the null values, ie. only column B will be set to 10. A and C will be left alone because they contain values.
Coalesce means pick the first item in the list that is not null.
The UPDATE statement only changes the fields you specify in the SET clause. If there are fields whose value you want left unmodified, then simply don't specify those fields in the SET clause.
Put another way, UPDATE doesn't write to all fields in the table - just the fields you specify for the rows you select with the WHERE clause.
If you simply don't know if the existing data is NULL or not, you can set the values using IFNULL(CurrentValue, NewValueIfNull). E.g.
UPDATE SET due_date=IFNULL(due_date, "some date") ... etc..
This will merge your new values into the row where there NULL values, and leave non-NULL values as they were.
See SQL Lite, IFNULL
How about:
UPDATE SET duedate='some date' WHERE _id=5 and duedate is null;
UPDATE SET priority='2' WHERE _id=5 and priority is null;
UPDATE SET details='some text' WHERE _id=5 and priority is null;
If you use Mysql, you can lookup IF()-then you can create a one liner. I think you can do something with similar in Oracle with case...
Related
There are multiple column in my table and I want to skip one column if value is null for that one particular column and all other columns should be updated with there respective value in oracle update query.
Is there any simple way to do this ?
Example:
Let me explain my problem with example:
I am using merge query like below :
merge into table_X on (condition )
WHEN MATCHED THEN
UPDATE SET COLUMN_1=VALUE1 , COLUMN_2=VALUE_2,........
WHEN NOT MATCHED THEN
INSERT ( COLUMN_1,COLUMN_2...) VALUES (VALUE_1,VALUE_2);
Now in update statement I want to skip the update for one column suppose COLUMN_2 if its value is null , but all other column should be updated . Basically I want to preserve the existing value when null is coming .
I have a main table that I am trying to update from a table that only has fields populated that need to be updated in the main table, using a unique ID to ensure I am updating only matched records. Here is what the SQL string looks like for the query:
UPDATE [tblMain] INNER JOIN tblUpdate ON tblMain.UUID = tblUpdate.UUID
SET tblMain.contractName = tblUpdate.contractName
WHERE ((tblUpdate.contractName) IS NOT NULL);
The idea is to only pull the fields from the update table that actually have data, and ignore the fields that are either NULL, blank, or empty. To be clear, I want to include ALL records in the tbleUpdate, but only update with the fields that contain data. How can I do this?
If you want to UPDATE one table from another in MS Access, you should do this
UPDATE tblMain, tblUpdate
SET tblMain.contractName = tblUpdate.contractName
WHERE tblMain.UUID = tblUpdate.UUID
AND tblUpdate.contractName IS NOT NULL
I need to insert hash value into column b based on value of column a, but I need to do this for every row in table.
I always get this error no matter what I tried:
ERROR: more than one row returned by a subquery used as an expression
I have been trying different versions of the following:
UPDATE table
SET column b = md5((SELECT column a FROM table))
WHERE column a IS NOT NULL;
Any suggestions on how to perform this operation?
No need for a subquery here. As I understand, you want to store the checksum of column_a in column_b. As one would expect, Postgres' md5() function expects a single, scalar argument of string datatype, so:
UPDATE table
SET column_b = md5(column_a)
WHERE column_a IS NOT NULL;
Note that it would probably be simpler to use a computed column (available in Postgres 12) to store this derived information.
if :p6_internal_id is null then
INSERT INTO table
(
id,
account
)
values
(
tseq_id.nextval,
:p6_account,
);
else
update table set "all columns" where id = :p6_internal_id;
end if ;
This says
ORA-00927: missing equal sign
for the update set "all columns" line.
I don't know how to fix this. How do I set the value of all the columns where id is what I enter?
Based on your comments, you just need to change that line to:
update table set account = :p6_account where id = :p6_internal_id;
You don't need to set the id column to :p6_internal_id as you know it already has that value - since you're using it in the where clause.
There is no magic value of '"all columns"' that would allow every column to be updated at once, not least because you need to supply a value that corresponds to every column anyway, and in the right order.
If you have multiple columns to set then you have to list them all explicitly, with each column/value pair separated by commas; e.g. with a few made-up columns and bind variables:
update table set account = :p6_account,
name = :p6_name,
amount := p6_amount
where id = :p6_internal_id;
You can see the required syntax in the documentation.
I want to make filtration on a column after selecting a specific value of another column in the same table, I tried to use #... special character followed by the column's name to get the address of this value.
My SQL statement is like the following :
SELECT ATTRIBUTE FROM TABLE WHERE FIELD = '#FIELDNAME';
If I used a specific value instead of #FIELDNAME, it will work properly but it will be static but I need it to be dynamic based on the selected value.
Create another table which will have the list of values that are in the FIELDNAME and give each record a unique id ,then retrieve the value depending on what you have selected by the name of the new table's field preceded by '#...'
I don't know if that what are you looking for, please let me know.
If no triggers are allowed, do you have any date/time column in the table? Is it possible to have that extra column anyway to see the time of a newly inserted row?
You may have to check the lastest row entered, save its field value into a variable. Then do the select based on the variable value.
Based on the vague last row id you could try the following (it's not pretty). But again, if you have date/time that's more accurate.
select attribute from table
where field = (select field from table
where rowid =(select max(rowid) from table))
;
upate
Do you have the priviledge to set up your insert command as below:
insert into table (id, col1, col2,...) values (1,'something', 'something',...)
returning id into variable; -- you may either save field or id depending on your table
Then you may use this variable to select the records you want.