Thank you for checking my question out!
I'm trying to write a query for a very specific problem we're having at my workplace and I can't seem to get my head around it.
Short version: I need to be able to target columns by their name, and more specifically by a part of their name that will be consistent throughout all the columns I need to combine or compare.
More details:
We have (for example), 5 different surveys. They have many questions each, but SOME of the questions are part of the same metric, and we need to create a generic field that keeps it. There's more background to the "why" of that, but it's pretty important for us at this point.
We were able to kind of solve this with either COALESCE() or CASE statements but the challenge is that, as more surveys/survey versions continue to grow, our vendor inevitably generates new columns for each survey and its questions.
Take this example, which is what we do currently and works well enough:
CASE
WHEN SURVEY_NAME = 'Service1' THEN SERV1_REC
WHEN SURVEY_NAME = 'Notice1' THEN FNOL1_REC
WHEN SURVEY_NAME = 'Status1' THEN STAT1_REC
WHEN SURVEY_NAME = 'Sales1' THEN SALE1_REC
WHEN SURVEY_NAME = 'Transfer1' THEN Null
ELSE Null
END REC
And also this alternative which works well:
COALESCE(SERV1_REC, FNOL1_REC, STAT1_REC, SALE1_REC) as REC
But as I mentioned, eventually we will have a "SALE2_REC" for example, and we'll need them BOTH on this same statement. I want to create something where having to come into the SQL and make changes isn't needed. Given that the columns will ALWAYS be named "something#_REC" for this specific metric, is there any way to achieve something like:
COALESCE(all columns named LIKE '%_REC') as REC
Bonus! Related, might be another way around this same problem:
Would there also be a way to achieve this?
SELECT (columns named LIKE '%_REC') FROM ...
Thank you very much in advance for all your time and attention.
-Kendall
Table and column information in Db2 are managed in the system catalog. The relevant views are SYSCAT.TABLES and SYSCAT.COLUMNS. You could write:
select colname, tabname from syscat.tables
where colname like some_expression
and syscat.tabname='MYTABLE
Note that the LIKE predicate supports expressions based on a variable or the result of a scalar function. So you could match it against some dynamic input.
Have you considered storing the more complicated properties in JSON or XML values? Db2 supports both and you can query those values with regular SQL statements.
Related
I'm still a bit of a noob, so pardon if this question is a bit obvious. I did search for an answer but either couldn't understand how the answers I found applied, or simply couldn't find an answer.
I have a massive database housed on a DB2 for i server which I'm accessing using SQL through SQLExplorer (based on Squirrel SQL). The tables are very poorly documented and the first order of business is figuring out how to find my way around.
I want to write a simple query that does this:
1) Allows me to search the entire database looking for tables that include a column called "Remarks" (which contains field descriptions).
2) I then want it to search that column for a keyword.
3) I want a table returned that includes the names of the tables that include that keyword (just the name, I can look up the table alphabetically later and look inside if I need to.)
I need this search to be super lightweight, and I'm hoping the concept I describe will achieve that. Anything that eats up a lot of resources will likely anger the sys admin for the server.
Just to show I have tried (and that I am a complete noob), here's what I've got so far.
SELECT *
FROM <dbname>
WHERE Remarks LIKE '<keyword>'
Feel free to mock, I told you I'm an idiot :-).
Any help? Perhaps at least a push in the right direction?
PS - I can't seem to find a search function in SQLExplorer, if someone knows if I can perhaps use a simple search or filter to accomplish this same goal...that would be great.
You can query the system catalog to identify the tables:
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME
FROM QSYS2.SYSCOLUMNS WHERE UPPER(DBILFL) = 'REMARKS'
And then query each table individually:
SELECT * FROM TABLE_SCHEMA.TABLE_NAME WHERE Remarks LIKE '%<keyword>%'
See the LIKE predicate for details of the pattern expression.
Normally i use something like this
SELECT TABLE_SCHEMA, TABLE_NAME
,COLUMN_NAME,SYSTEM_COLUMN_NAME,COLUMN_HEADING
,DATA_TYPE, "LENGTH",NUMERIC_SCALE
FROM QSYS2.SYSCOLUMNS
WHERE UPPER(COLUMN_NAME) LIKE '%REMARK%'
#JamesA, i'm at V6R1, by default, normal user are not authorized to object QADBIFLD in QSYS
Generally, many if not most IBM i shops (especially those that use RPG) stick to 10 (or less) character schema names & table names, and have a 10 (or less) character names for 'system' column names, even if longer column names are also provided. Column text generally describes each field.
SELECT SYSTEM_TABLE_SCHEMA, SYSTEM_TABLE_NAME
,SYSTEM_COLUMN_NAME,
,DATA_TYPE, "LENGTH",NUMERIC_SCALE
,CHAR(COLUMN_TEXT)
FROM QSYS2.SYSCOLUMNS
WHERE UPPER(COLUMN_NAME) LIKE '%REMARK%'
I'm building an abstract gem. i need a sql query that looks like this
SELECT * FROM my_table WHERE * LIKE '%my_search%'
is that possible?
edit:
I don't care about querys performance because it's a feature function of a admin panel, which is used once a month. I also don't know what columns the table has because it's so abstract. Sure i could use some rails ActiveRecord functions to find all the columns but i hoped to avoid adding this logic and just using the *. It's going to be a gem, and i can't know what db is going to be used with it. Maybe there is a sexy rails function that helps me out here.
As I understand the question, basically you are trying to build a sql statement which should check for a condition across all columns in that table. A dirty hack, but this generates the required Sql.
condition_string = MyTable.column_names.join(' LIKE ? OR ')
MyTable.all(:conditions => [condition_string, '%my_search%'])
However, this is not tested. This might work.
* LIKE '...' isn't valid according to the SQL standards, and not supported by any RDBMS I'm aware of. You could try using a function like CONCAT to make the left argument of LIKE, though performance won't be good. As for SELECT *, it's generally something to be avoided.
No, SQL does not support that syntax.
To search all columns you need to use procedures or dynamic SQL. Here's another SO question which may help:
SQL: search for a string in every varchar column in a database
EDIT: Sorry, the question I linked to is looking for a field name, not the data, but it might help you write some dynamically SQL to build the query you need.
You didn't say which database you are using, as there might be a vendor specific solution.
Its only an Idea, but i think it worth testing!
It depends on your DB you can get all Columns of a table, in MSSQL for example you can use somethink like:
select name from syscolumns where id=object_id('Tablename')
Under Oracle guess its like:
select column_name from USER_TAB_COLUMNS where TABLE_NAME = 'Tablename'
and then you will have to go through these columns usign a procedure and maby a cursor so you can check for each Column if the data your searching for is in there:
if ((select count(*) from Tablename where Colname = 'searchingdata') > 0)
then keep the results in a separated table(ColnameWhereFound, RecNrWhereFound).
The matter of Datatye may be an Issue if you try to compare strings with numbers, but if you notice for instance under SQL-Server the syscolumns table contains a column called "usertype" which contains a number seems to refer to the Datatype stored in the Columne, like 2 means string and 7 means int, and 2 means smallint, guess Oracle would have something similar too.
Hope this helps.
I am wondering how others would handle a scenario like such:
Say I have multiple choices for a user to choose from.
Like, Color, Size, Make, Model, etc.
What is the best solution or practice for handling the build of your query for this scneario?
so if they select 6 of the 8 possible colors, 4 of the possible 7 makes, and 8 of the 12 possible brands?
You could do dynamic OR statements or dynamic IN Statements, but I am trying to figure out if there is a better solution for handling this "WHERE" criteria type logic?
EDIT:
I am getting some really good feedback (thanks everyone)...one other thing to note is that some of the selections could even be like (40 of the selections out of the possible 46) so kind of large. Thanks again!
Thanks,
S
What I would suggest doing is creating a function that takes in a delimited list of makeIds, colorIds, etc. This is probably going to be an int (or whatever your key is). And splits them into a table for you.
Your SP will take in a list of makes, colors, etc as you've said above.
YourSP '1,4,7,11', '1,6,7', '6'....
Inside your SP you'll call your splitting function, which will return a table-
SELECT * FROM
Cars C
JOIN YourFunction(#models) YF ON YF.Id = C.ModelId
JOIN YourFunction(#colors) YF2 ON YF2.Id = C.ColorId
Then, if they select nothing they get nothing. If they select everything, they'll get everything.
What is the best solution or practice for handling the build of your query for this scenario?
Dynamic SQL.
A single parameter represents two states - NULL/non-existent, or having a value. Two more means squaring the number of parameters to get the number of total possibilities: 2 yields 4, 3 yields 9, etc. A single, non-dynamic query can contain all the possibilities but will perform horribly between the use of:
ORs
overall non-sargability
and inability to reuse the query plan
...when compared to a dynamic SQL query that constructs the query out of only the absolutely necessary parts.
The query plan is cached in SQL Server 2005+, if you use the sp_executesql command - it is not if you only use EXEC.
I highly recommend reading The Curse and Blessing of Dynamic SQL.
For something this complex, you may want a session table that you update when the user selects their criteria. Then you can join the session table to your items table.
This solution may not scale well to thousands of users, so be careful.
If you want to create dynamic SQL it won't matter if you use the OR approach or the IN approach. SQL Server will process the statements the same way (maybe with little variation in some situations.)
You may also consider using temp tables for this scenario. You can insert the selections for each criteria into temp tables (e.g., #tmpColor, #tmpSize, #tmpMake, etc.). Then you can create a non-dynamic SELECT statement. Something like the following may work:
SELECT <column list>
FROM MyTable
WHERE MyTable.ColorID in (SELECT ColorID FROM #tmpColor)
OR MyTable.SizeID in (SELECT SizeID FROM #tmpSize)
OR MyTable.MakeID in (SELECT MakeID FROM #tmpMake)
The dynamic OR/IN and the temp table solutions work fine if each condition is independent of the other conditions. In other words, if you need to select rows where ((Color is Red and Size is Medium) or (Color is Green and Size is Large)) you'll need to try other solutions.
In the process of fixing a poorly imported database with issues caused by using the wrong database encoding, or something like that.
Anyways, coming back to my question, in order to fix this issues I'm using a query of this form:
UPDATE table_name SET field_name =
replace(field_name,’search_text’,'replace_text’);
And thus, if the table I'm working on has multiple columns I have to call this query for each of the columns. And also, as there is not only one pair of things to run the find and replace on I have to call the query for each of this pairs as well.
So as you can imagine, I end up running tens of queries just to fix one table.
What I was wondering is if there is a way of either combine multiple find and replaces in one query, like, lets say, look for this set of things, and if found, replace with the corresponding pair from this other set of things.
Or if there would be a way to make a query of the form I've shown above, to run somehow recursively, for each column of a table, regardless of their name or number.
Thank you in advance for your support,
titel
Let's try and tackle each of these separately:
If the set of replacements is the same for every column in every table that you need to do this on (or there are only a couple patterns), consider creating a user-defined function that takes a varchar and returns a varchar that just calls replace(replace(#input,'search1','replace1'),'search2','replace2') nested as appropriate.
To update multiple columns at the same time you should be able to do UPDATE table_name SET field_name1 = replace(field_name1,...), field_name2 = replace(field_name2,...) or something similar.
As for running something like that for every column in every table, I'd think it would be easiest to write some code which fetches a list of columns and generates the queries to execute from that.
I don't know of a way to automatically run a search-and-replace on each column, however the problem of multiple pairs of search and replace terms in a single UPDATE query is easily solved by nesting calls to replace():
UPDATE table_name SET field_name =
replace(
replace(
replace(
field_name,
'foo',
'bar'
),
'see',
'what',
),
'I',
'mean?'
)
If you have multiple replaces of different text in the same field, I recommend that you create a table with the current values and what you want them replaced with. (Could be a temp table of some kind if this is a one-time deal; if not, make it a permanent table.) Then join to that table and do the update.
Something like:
update t1
set field1 = t2.newvalue
from table1 t1
join mycrossreferncetable t2 on t1.field1 = t2.oldvalue
Sorry didn't notice this is MySQL, the code is what I would use in SQL Server, my SQL syntax may be different but the technique would be similar.
I wrote a stored procedure that does this. I use this on a per database level, although it would be easy to abstract it to operate globally across a server.
I would just paste this inline, but it would seem that I'm too dense to figure out how to use the markdown deal, so the code is here:
http://www.anovasolutions.com/content/mysql-search-and-replace-stored-procedure
I am doing a simple SELECT statement in an Oracle DB and need to select the columns in a somewhat-specific order. Example:
Table A has 100 attributes, one of which is "chapter" that occurs somewhere in the order of columns in the table. I need to select the data with "chapter" first and the remaining columns after in no particular order. Essentially, my statement needs to read something like:
SELECT a.chapter, a. *the remaining columns* FROM A
Furthermore, I cannot simply type:
SELECT a.chapter, a.*
because this will select "chapter" twice.
I know the SQL statement seems simple, but if I know how to solve this problem, I can extrapolate this thought into more complicated areas. Also, let's assume that I can't just scroll over to find the "chapter" column and drag it to the beginning.
Thanks.
You should not select * in a program. As your schema evolves it will bring in things you do not know yet. Think about what happens when someone add a column with the whole book in it? The query you thought would be very cheap suddenly starts to bring in megabytes of data.
That means you have to specify every column you need.
Your best bet is just to select each column explicitly.
A quickie way to get around this would be SELECT a.chapter AS chapterCol, a.* FROM table a; This means there will be one column name chapterCol (assuming there's not a column already there named chapterCol. ;))
If your going to embed the 'SELECT *' into program code, then I would strongly recommend against doing that. As noted by the previous authors, your setting up the code to break if a column is ever added to (or removed from) the table. The simple advice is don't do it.
If your using this in development tools (viewing the data, and the like). Then, I'd recommend creating a view with the specific column order you need. Capture the output from 'SELECT COLUMN_NAME FROM ALL_TAB_COLUMNS' and create a select statement for the view with the column order you need.
This is how I would build your query without having to type all the names in, but with some manual effort.
Start with "Select a.chapter"
Now perform another select on your data base as follows :
select ','|| column_name
from user_tab_cols
where table_name = your_real_table_name
and column_name <> 'CHAPTER';
now take the output from that, in a cut-and-paste manner and append it to what you started with. Now run that query. It should be what you asked for.
Ta-da!
Unless you have a very good reason to do so, you should not use SELECT * in queries. It will break your application every time the schema changes.