First off: I am reverse engineering SQL queries and as a result I have a bunch of candidate queries, which all contain a designated 'entity' column in their SELECT clause.
The problem is: I want the entity column to be the first column of my result and let all the other columns follow, so basically I want something like this
SELECT A.entity, *
FROM A
...
...but without the duplicate entity column resulting from the *-operator.
EDIT: I also do not know all of the column names, generally only the entity column name is known.
Thanks for helping me
Related
Hey guys, maybe this is a basic SQL qn. Say I have this very simple table, I need to run a simple sql statement to return a result like this:
Basically, the its to dedup Name based on it's row's Value column, whichever is larger should stay.
Thanks!
Framing the problem correctly would help you figure it out.
"Deduplication" suggests altering the table - starting with a state with duplicates, ending with a state without them. Usually done in three steps (getting the rows without duplicates into temp table, removing original table, renaming temp table).
"Removing rows with duplicated column values" also suggests alteration of data and derails train of thought.
What you do want is to get the entire table, and in cases where the columns you care about have multiple values attached get the highest one. One could say... group by columns you care about? And attach them to the highest value, a maximum value?
select id,name,max(value) from table group by id,name
I'm trying to achieve 2 joins. If I run the 1st join alone it pulls 4 lots of results, which is correct. However when I add the 2nd join which queries the same reference table using the results from the select statement it pulls in additional results. Please see attached. The squared section should not be being returned
So I removed the 2nd join to try and explain better. See pic2. I'm trying to get another column which looks up InvolvedInternalID against the initial reference table IRIS.Practice.idvClient.
Your database is simply doing as you tell it. When you add in the second join (confusingly aliased as tb1 in a 3 table query) the database is finding matching rows that obey the predicate/truth statement in the ON part of the join
If you don't want those rows in there then one of two things must be the case:
1) The truth you specified in the ON clause is faulty; for example saying SELECT * FROM person INNER JOIN shoes ON person.age = shoes.size is faulty - two people with age 13 and two shoes with size 13 will produce 4 results, and shoe size has nothing to do with age anyway
2) There were rows in the table joined in that didn't apply to the results you were looking for, but you forgot to filter them out by putting some WHERE (or additional restriction in the ON) clause. Example, a table holds all historical data as well as current, and the current record is the one with a NULL in the DeletedOn column. If you forget to say WHERE deletedon IS NULL then your data will multiply as all the past rows that don't apply to your query are brought in
Don't alias tables with tbX, tbY etc.. Make the names meaningful! Not only do aliases like tbX have no relation to the original table name (so you encounter tbX, and then have to go searching the rest of the query to find where it's declared so you can say "ah, it's the addresses table") but in this case you join idvclient in twice, but give them unhelpful aliases like tb1, tb3 when really you should have aliased them with something that describes the relationship between them and the rest of the query tables
For example, ParentClient and SubClient or OriginatingClient/HandlingClient would be better names, if these tables are in some relationship with each other.
Whatever the purpose of joining this table in twice is, alias it in relation to the purpose. It may make what you've done wriong easier to spot, for example "oh, of course.. i'm missing a WHERE parentclient.type = 'parent'" (or WHERE handlingclient.handlingdate is not null etc..)
The first step to wisdom is by calling things their proper names
I can't find the hql to solve my problem.
I have 2 nice tables.
The first table has a column with strings in the form 'xxx-xxx-xxx'.
The second table has a column with strings in the form 'some_prefix:xxx-xxx-xxx'.
What I want to do is given a subset of rows in the second table, find all the entries in the first table that match in the 'xxx-xxx-xxx' part. And I know for sure there cannot be more that one entry in the fist table for each row in the second.
I'm looking for a hql query that fetches those objects but I could use a sql too.
Cheers.
you can use a combination of locate and substring function on column of the second table to get the string after the : sign.
I haven't tested it but it should be something like:
where table1.column = substring(table2.column, locate(table2.column, ':'))
Suppose I have one table A, with 10 fields. And Table B, with 5 fields.
B links to A via a column named "key", that exists both in A, and in B, with the same name ("key").
I am generating a generic piece of SQL, that queries from a main table A, and receives a table name parameter to join to, and select all A fields + B.
In this case, I will get all the 15 fields I want, or more precisely - 16, because I get "key" twice, once from A and once from B.
What I want is to get only 15 fields (all fields from the main table + the ones existing in the generic table), without getting "key" twice.
Of course I can explicit the fields I want in the SELECT itself, but that thwarts my very objective of building a generic SQL.
It really depends on which RDBMS you're using it against, and how you're assembling your dynamic SQL. For instance, if you're using Oracle and it's a PL/SQL procedure putting together your SQL, you're presumably querying USER_TAB_COLS or something like that. In that case, you could get your final list of columns names like
SELECT DISTINCT(column_name)
FROM user_tab_cols
WHERE table_name IN ('tableA', 'tableB');
but basically, we're going to need to know a lot more about how you're building your dynamic SQL.
Re-thinking about what I asked makes me conclude that this is not plausible. Selecting columns in a SELECT statement picks the columns we are interested in from the list of tables provided. In cases where the same column name exists in more than one of the tables involved, which are the cases my question is addressing, it would, ideally, be nice if the DB engine could return a unique list of fields - BUT - for that it would have to decide itself which column (and from which table) to choose, from all the matches - which is something that the DB cannot do, because it is solely dependent in the user's choice.
I want to return columns based on some meta data in an other table. i.e. i have my table which contains 10 columns, and another table which contains those columns denormalise with metadata to do with them.
i.e.
Table - Car:
columns - Make,Model,Colour
and another table called "Flags" which has a row for each of the above columns and each row has a column for "IsSearchable" and "ShowOnGrid" - that sort of thing.
The query i want is one which will return all columns from the cars table that are flagged in the "Flags" table as "ShowInGrid"
----EDIT
Apologise, I should have stated that this is on SQL Server 2008.
Also, I dont want to have to physically state the columns which i would like to return, i.e. If i add a column to the car table, then add it into the Flags table and declare it to be searchable, I don't want to have to physically state in the SQL Query that i want to return that column, i want it to automatically pull through.
You need to use dynamic SQL; this can easily be done with a stored procedure.
Something like this might work:
Select
D.CarID,
Case D.ShowMake When True Then D.Make Else NULL END AS Make
...
From
(Select
C.CarID, C.Make, C.Model, C.Colour, F.IsSearchable, F.ShowOnGrid, F.ShowMake
From
Cars C
Inner Join
Flags F
On C.CarID = F.CarID) D
I didn't write in all the case statements and don't know how many flags you're working, but you can give it a try. It would require to filter on null values in your application. If you actually want the columns omitted on the basis of the Flag column value the other answer and comment are both right on. Either Dynamic SQL or build your query outside in another language first.