How do I implement such scenario in Teradata
If Col1 is null or if Col1 = ''Jack'' then Col2 else Col1
I ha e implemented it but for some reason it's not working may be some issue with Bracketay
You can also use the NULLIF() operator:
COALESCE(NULLIF(col1,'Jack'), col2)
This is logically equivalent to the CASE statement in the previous answer.
You can use a case expression:
case
when col1 is null or col1 = 'Jack' then col2
else col1
end
String (varchar) constants need to be enclosed in sinqle quotes in SQL.
Related
I have a table with more than 15 columns. 2 of of them are of the type varchar, and most of them of type int and float.
I am new to SQL and am trying to figure out a way by which I can check if any of the columns have a NULL value in it.
Had there been just 4 or 5 columns I could have checked them individually with
SELECT COUNT(*) FROM table_name WHERE col1 IS NULL OR col2 IS NULL OR col3 IS NULL ...
But is there any efficient way to do this on a lot of columns in SQLite specifically?
I have referred to other questions regarding this here but I cannot use xml or store anything. Also I am using SQLite and can only run a query.
There is no way (that I know of) to check all columns if they contain null without explicitly listing all the column names.
Your query is the proper way to do it.
If you want to shorten (not significantly) the code you could use these alternatives:
SELECT COUNT(*) FROM table_name WHERE col1 + col2 + col3 IS NULL;
or:
SELECT COUNT(*) FROM table_name WHERE col1 || col2 || col3 IS NULL;
or:
SELECT COUNT(*) FROM table_name WHERE MAX(col1, col2, col3) IS NULL;
The above queries work, for any data type of the columns, because if there is even only 1 column equal to null then addition, concatenation and the scalar function MAX() (and MIN()) all return null.
See the demo.
Is it possible to check multiple Expressions inside "Decode" function in PL SQL.
My requirement is basically
SELECT value1,
DECODE(Expression1 AND Expression2,
search1 , search2,
,'pass result',
'fail result') value2
FROM dual;
Or is there are workaround for this?
The simplest answer is don't use decode, use a case statement instead, e.g.
select 1 value1,
case when 'a' = 'a' and 'b' = 'b' then 'pass'
else 'fail'
end result
from dual;
VALUE1 RESULT
---------- ------
1 pass
It is possible to use DECODE, but you'd have to use nested DECODEs and you'd end up with something that's much harder to read, understand and therefore maintain. And what happens if you need to add a third condition? Or maybe there are multiple sets of results that would result in a pass? You'd end up with something truly horrendous to try and understand!
But, if you really must, here's an example (along with the corresponding CASE expression solution, which is (IMHO) much easier to read):
with sample_data AS (SELECT 1 ID, 'a' col1, 'b' col2 FROM dual UNION ALL
SELECT 2 ID, 'a' col1, 'c' col2 FROM dual UNION ALL
SELECT 3 ID, 'd' col1, 'b' col2 FROM dual UNION ALL
SELECT 4 ID, 'e' col1, 'f' col2 FROM dual)
SELECT ID,
CASE WHEN col1 = 'a' AND col2 = 'b' THEN 'pass'
ELSE 'fail'
END case_result,
DECODE(col1, 'a', DECODE(col2, 'b', 'pass',
'fail'),
'fail') decode_result
FROM sample_data;
ID CASE_RESULT DECODE_RESULT
---------- ----------- -------------
1 pass pass
2 fail fail
3 fail fail
4 fail fail
I'm trying to find use RODBCext syntax for multiple parms in the same query with at least one of them part of an IN clause.
This is the approach I'm taking, but it doesn't like the IN part:
Error: unexpected symbol in "AND col2 "
This is how I'm specifying the parms:
prm <- data.frame( '2', c('B01', 'B12', 'B23', 'B34', 'B45'))
This is the SQL"
dataResult <- sqlExecute, connHandle, query = "
select col1, col2, col3
from tblA
where col1 = ?
and col2 IN ?
"
, prm
, fetch = TRUE)
odbcClose(connHandle)
I've looked at the CRAN pdf
and
the vignettes
I resolved this by changing the syntax to use OR rather than IN. This makes it harder to read, but the code runs successfully.
How do I set unique constraint over multiple columns when any one can be null in SQLite?
e.g. I have made unique("col1","col2","col3") and tried insert into tablename values("abc","def",null) twice it inserted both rows.
The unique constraint is not working when third column is null.
In sqlite, all null are differences.
I think the best way to solve this issue is to set column c not null with a special default value. Then use the default value (for example 0, '') to represent null.
edit 1
you can easily extend this solution to any columns
create table test (
a text not null default "",
b text not null default "",
c text not null default ""
);
You could create a trigger to enfore this:
CREATE TRIGGER col1_col2_col3null_unique
BEFORE INSERT ON MyTable
FOR EACH ROW
WHEN col1 IS NOT NULL
AND col2 IS NOT NULL
AND col3 IS NULL
BEGIN
SELECT RAISE(ABORT, 'col1/col2/col3 must be unique')
FROM MyTable
WHERE col1 = NEW.col1
AND col2 = NEW.col2
AND col3 IS NULL;
END;
You need such a trigger for each possible combination of NULLs in the three columns.
Furthermore, if it is possible to have UPDATEs that change such a column to NULL, you need triggers for those, too.
Starting with version 3.9.0 (2015-10-14) you can use indexes on expressions (https://www.sqlite.org/expridx.html) and use for example the COALESCE function to transform null values into some form of fallback value:
CREATE UNIQUE INDEX IX_Unique ON Table1 (
COALESCE(col1, ""),
COALESCE(col2, ""),
COALESCE(col3, "")
);
Can I use DECODE in a UPDATE statement on the left hand side of SET?
UPDATE temp SET DECODE(update_var, 1, col1,
2, col2) = update_value;
This is giving me error as eual sign ignored..
How about this? If the update flag is set to 1, col1 gets updated, if set to 2, then col2 gets updated.
UPDATE temp
SET col1 = DECODE(update_var, 1, update_value, col1),
col2 = DECODE(update_var, 2, update_value, col2)
Also, as a bonus, it'll handle the possible situation where the update variable is set to something other than one or two!
No you can't do that. You can do this in PL/SQL:
IF update_var = 1 THEN
UPDATE temp SET col1 = update_value;
else
UPDATE temp SET col2 = update_value;
END IF;
Or you could use dynamic SQL like this:
l_sql := 'UPDATE temp SET col'||update_var||' = :v';
EXECUTE IMMEDIATE l_sql USING update_value;
You cant use decode in an update statement.
You can however use a merge statement.
http://psoug.org/reference/merge.html
MERGE INTO temp b
USING (
SELECT key, DECODE(update_var, 1, update_value, col1) as col1,
DECODE(update_var, 2, update_value, col2) as col2
FROM temp
WHERE key =theKeyIPassedIn) e
ON (b.key = e.key)
WHEN MATCHED THEN
UPDATE SET b.col1 = e.col1, b.col2 = e.col2
;
Basically you are using the select portion of the merge to decode col1 and col2 to either the update_value or the value that exists already.
This may also be too verbose for your needs, and the solution that uses an if statement or execute immediate may better suit your problem.