I wish to do something like this:
DECLARE #IgnoreNulls = 1;
SELECT Col1, Col2
FROM tblSimpleTable
IF #IgnoreNulls
BEGIN
WHERE Col2 IS NOT NULL
END
ORDER BY Col1 DESC;
The idea is to, in a very PHP/ASP.NET-ish kinda way, only filter NULLs if the user wishes to. Is this possible in T-SQL? Or do we need one large IF block like so:
IF #IgnoreNulls
BEGIN
SELECT Col1, Col2
FROM tblSimpleTable
WHERE Col2 IS NOT NULL
ORDER BY Col1 DESC;
END
ELSE
BEGIN
SELECT Col1, Col2
FROM tblSimpleTable
ORDER BY Col1 DESC;
END
You can do that this way:
SELECT Col1, Col2
FROM tblSimpleTable
WHERE ( #IgnoreNulls != 1 OR Col2 IS NOT NULL )
ORDER BY Col1 DESC
Dynamically changing searches based on the given parameters is a complicated subject and doing it one way over another, even with only a very slight difference, can have massive performance implications. The key is to use an index, ignore compact code, ignore worrying about repeating code, you must make a good query execution plan (use an index).
Read this and consider all the methods. Your best method will depend on your parameters, your data, your schema, and your actual usage:
Dynamic Search Conditions in T-SQL by by Erland Sommarskog
In general (unless the table is small) the best approach is to separate out the cases and do something like you have in your question.
IF (#IgnoreNulls = 1)
BEGIN
SELECT Col1, Col2
FROM tblSimpleTable
WHERE Col2 IS NOT NULL
ORDER BY Col1 DESC;
END
ELSE
BEGIN
SELECT Col1, Col2
FROM tblSimpleTable
ORDER BY Col1 DESC;
END
This is less likely to cause you problems with sub optimal query plans being cached.
Related
I need to do some comparison through 3 columns containing string dates 'yyyy-mm-dd', in Hive SQL. Please take in consideration that the table has more than 2 million records.
Consider three columns (col1; col2; col3) from table T1, I must guarantee that:
col1 = col2, and both, or at least one is different from col3.
My best regards,
Logically you have an issue.
col1 = col2
Therefore if col1 != col3 then col2 != col3;
There for it's really enough to use:
select * from T1 where col1 = col2 and col1 != col3;
It is appropriate to do this map side so using a where criteria is likely good enough.
If you wanted to say 2 out of the 3 need to match you could use group by with having to reduce comparisons.
I'm not too sure how to describe my SQL Insert statement so I will describe the expected result.
I'm building a data extract list and have a table that I've put all my data into. It's called _MATTER_LIST
What I am trying to Achieve is to have the Client_Number + Col1 combination repeat after every unique COL1+COL2+COL3 combination but not duplicate when there is already a CLIENT_NUMBER+COL1. So the end result would be:
thanks in advance for any tips.
Simple ORDER BY should work for you if i understand. Try this :
select Client_Number, Col1, Col2, Col3 from _MATTER_LIST
order by Client_Number, Col1
I've managed to fix my own issue. I added a unique key for the col1 + col2 + col3 , then make col2 repeat over each combination for example.
The result is: select * from _MATTER_LIST order by COL4, COL5
I would like to write a query
Select col1, col2
from table
where col1 = 'blah' or 'blah2' or 'blah3'
and col2 = 'blah' or 'blah2' or 'blah3'
I am used to writing them like this for a SINGLE option
select
col1, col2
from
table
where
col1 = :col1 and col2 = :col2
Parameters.AddWithValue(":col1", 'blah')
Parameters.AddWithValue(":col2", 'blah')
Now I want to add several options with OR between them and obviously the above code wont work. The SQL is for SQLite. Can anyone suggest how I could do this? I may potential have more then 3 different values for each parameter. I have tried searching but the answer is elusive.
You still have to use complete expressions, i.e., you need to write col1 = or col2 = every time.
Alternative, use IN:
SELECT ... WHERE col1 IN (:c11, :c12, :c13) AND col2 IN (:c21, :c22, :c23);
I am trying to write a PL/SQL procedure which will have the SQL query to get the results. But the requirement is that the order by can be dynamic and is mainly for sorting the columns in the screen. I am passing 2 parameters to this procedure - in_sort_column and in_sort_order.
The requirement is such that on text columns the sorting is in ASC and for numbers it is DESC.
My query looks something like this without adding the in_sort_order -
SELECT col1, col2, col3 from tabl e1 where col1 > 1000
ORDER BY decode(in_sort_column,'col1', col1, 'col2', col2, 'col3', col3);
I am not able to figure out how to use the in_sort_order parameter in this case. Can someone who has done this before help out ?
Thanks
When doing a dynamic sort, I recommend using separate clauses:
order by (case when in_sort_column = 'col1' then col1 end),
(case when in_sort_column = 'col2' then col2 end),
(case when in_sort_column = 'col3' then col3 end)
This guarantees that you will not have an unexpected problem with type conversion, if the columns are of different types. Note that case return NULL without an else clause.
Since the requirement is based on data type, you could just negate the numeric columns in your decode; if col1 is numeric and the others are text then:
ORDER BY decode(in_sort_column, 'col1', -col1, 'col2', col2, 'col3', col3);
But this is going to attempt to convert the text columns to numbers. You can swap the decode or around to avoid that, but you then do an implicit conversion of your numeric column to a string, and your numbers will then be sorted alphabetically - so 2 comes after 10, for example.
So Gordon Linoff's use of case is better, and you can still negate the col1 value with that to make the numbers effectively sort descending.
In WHERE clause when using condition like this Table.Column = #Param OR #Param IS NULL It does not use INDEX on Column.
Is it true and if so then how to write this kind of query which also use INDEX
Query Example
SELECT Col1, Col2 ...
FROM Table
WHERE (Col1 = #col OR #col IS NULL)
AND (Col2 = #col2 OR #col2 IS NULL)
AND (Col3 = #col3 OR #col3 IS NULL)
Any help.
Unfortunately, the generation of execution plans does not behave as you expect.
For that single query, a single plan is created. In creating that plan the indexes to use are selected, and fixed. It doesn't matter what parameters you provide, the same plan, same indexes, etc, are always used.
The otpimiser has tried to find the best plan that can fit all eventuallities, but by the nature of this type of query, there isn't one. A characteristic born out by the plan you have not using an index at all.
The solution is to use dynamic SQL. This feels untidy, but if you use parameterised queries with sp_executesql, it can actually be quite stuctured, and very performant.
Here is a link to a very useful article on the subject: dynamic search
It's very in depth, but it is a very robust approach to this problem.
SELECT Col1, Col2 ...
FROM Table
WHERE EXISTS(
SELECT Col1, Col2, Col3
INTERSECT
SELECT #col, #col2, #col3)
Intuitively, this seems like it should perform very badly, but SQL Server's query optimiser knows how to give INTERSECT special treatment, and internally translates it to (pseudo-SQL)
SELECT Col1, Col2 ...
FROM Table
WHERE (Col1, Col2, Col3) IS (#col, #col2, #col3)
as you can see in the query plan. If you have indices on these columns, they can and do get used.
I originally picked this up from Paul White's Undocumented Query Plans: Equality Comparisons blog post, which may be an interesting further read.
Why don't try this:
SELECT Col1, Col2 ...
FROM Table
WHERE Col1 = IsNull(#col,Col1)
AND Col2 = IsNull(#col2,Col2)
AND Col3 = IsNull(#col3,Col3)
About your question:
Your query analyzer say it don't use the index on column1,2,3 ? You made a index for all 3 columns? Then it should use it regardless the other OR IS NULL
Try to have index on all where clause columns and try to use the more structured query as given below:
SELECT Col1, Col2 ...
FROM Table
WHERE Col1 = **COALESCE**(#col,Col1)
AND Col2 = **COALESCE**(#col2,Col2)
AND Col3 = **COALESCE**(#col3,Col3)
The COALESCE() function returns the first non-null argument so if STATUS is NULL it will return ''.