how to get data from a specific column in fire bird? something like.
select from rdb$relation_fields
where rdb$relation_name = 'table' and rdb$field_name = 'code'
Your question doesn't quite make sense to me - if you already know the table and field name (as you do in your example) then why not select directly from the table? Anyway, you can create SQL statement dynamically in PSQL as string and then execute it using EXECUTE STATEMENT. The EXECUTE BLOCK might also be of intrest, depends where and what exactly youre tring to achieve.
EDIT after reading the comment
So just build the SELECT statement at the client side, selecting the field currently selected in combobox. You don't mention the language you use but generaaly it something like
query.SQL := 'SELECT '+ comboField.Text +' FROM '+curTableName;
query.Open();
// read the resultset
Related
I'm using a PostgreSQL with a Go driver. Sometimes I need to query not existing fields, just to check - maybe something exists in a DB. Before querying I can't tell whether that field exists. Example:
where size=10 or length=10
By default I get an error column "length" does not exist, however, the size column could exist and I could get some results.
Is it possible to handle such cases to return what is possible?
EDIT:
Yes, I could get all the existing columns first. But the initial queries can be rather complex and not created by me directly, I can only modify them.
That means the query can be simple like the previous example and can be much more complex like this:
WHERE size=10 OR (length=10 AND n='example') OR (c BETWEEN 1 and 5 AND p='Mars')
If missing columns are length and c - does that mean I have to parse the SQL, split it by OR (or other operators), check every part of the query, then remove any part with missing columns - and in the end to generate a new SQL query?
Any easier way?
I would try to check within information schema first
"select column_name from INFORMATION_SCHEMA.COLUMNS where table_name ='table_name';"
And then based on result do query
Why don't you get a list of columns that are in the table first? Like this
select column_name
from information_schema.columns
where table_name = 'table_name' and (column_name = 'size' or column_name = 'length');
The result will be the columns that exist.
There is no way to do what you want, except for constructing an SQL string from the list of available columns, which can be got by querying information_schema.columns.
SQL statements are parsed before they are executed, and there is no conditional compilation or no short-circuiting, so you get an error if a non-existing column is referenced.
I basically have a void function that creates a tuple on a existing table. Now at the end of the function I want display the table with the updated tuple. I am running it problems when trying to do this.
This is the statement I am using:
EXECUTE 'SELECT * FROM table WHERE IDNo = idnumber';
-- (idnumber is a variable that is assigned a value in the function)
I get the following error:
ERROR: column "idnumber" does not exist.
Can someone please help me find a solution.
For the actual query, you would want to do something like this:
execute 'select * from table where IDNo = $1' using idnumber;
With the key being the $1 and the USING clause to interpolate the variable.
That should resolve the column error regarding idnumber.
However, I'm not quite sure what you mean by:
display the table with the updated tuple
Do you mean you want to return all the rows in the table including the newly added row? Or just the newly added row? or something else?
Edit in response to comment from OP:
The substitution variables, e.g. $1, $2, $3... are scoped (i.e. unique) to each separate execute statement. So if you had two statements, the first with 3 variables, the second with three, you could use $1, $2, $3 in each and they would refer to the variables mentioned in the USING clause for that individual statement.
See the Postgres Basic Statements doc, specifically the section entitled 40.5.4. Executing Dynamic Commands, for more detail.
Second edit in response to display comments from OP:
When executeing statements, they won't output the way, say, a select statement would if you were doing it within psql or pgadmin. Rather, you have a couple different options, depending on what you ultimately want to do.
First, you could use an INTO clause to put the result into a record (although how you do this depends on whether it's just one row or many rows).
You would need to declare it in that case in the declaration section something like this: foo RECORD;
And then add INTO foo before the USING clause. If it complains about more than one record, you could add LIMIT 1 clause at the end of the query.
You could then do whatever else you wanted to with that record, including RAISE NOTICE with interpolating the record's columns, which would print it to the console.
If you want the entire table, and you want it to "display" more like psql or similar would (that is, return the rows obtained), you would want to have the function return a setof a specific type.
So it may then look something like this:
create function get_table() returns setof table as $$
execute 'select * from table where IDNo = $1' using idnumber;
$$ language 'plpgsql';
Where table is the name of the table you want. If you just want to return the existing rows of the table, this sort of query should work. It would then "display" in a client (e.g. psql, etc.) as the result set.
If you want to modify that (say, by dynamically adding some columns), then you would need to define that new type specifically, and then use that as the type being returned.
See the Postgres Wiki for more details. The wiki content is pretty old (Postgres 7.x vintage), but it generally still applies.
In my table results from column work_time (interval type) display as 200:00:00. Is it possible to cut the seconds part, so it will be displayed as 200:00? Or, even better: 200h00min (I've seen it accepts h unit in insert so why not load it like this?).
Preferably, by altering work_time column, not by changing the select query.
This is not something you should do by altering a column but by changing the select query in some way. If you change the column you are changing storage and functional uses, and that's not good. To change it on output, you need to modify how it is retrieved.
You have two basic options. The first is to modify your select queries directly, using to_char(myintervalcol, 'HH24:MI')
However if your issue is that you have a common format you want to have universal access to in your select query, PostgreSQL has a neat trick I call "table methods." You can attach a function to a table in such a way that you can call it in a similar (but not quite identical) syntax to a new column. In this case you would do something like:
CREATE OR REPLACE FUNCTION myinterval_nosecs(mytable) RETURNS text LANGUAGE SQL
IMMUTABLE AS
$$
SELECT to_char($1.myintervalcol, 'HH24:MI');
$$;
This works on the row input, not on the underlying table. As it always returns the same information for the same input, you can mark it immutable and even index the output (meaning it can be run at plan time and indexed used).
To call this, you'd do something like:
SELECT myinterval_nosecs(m) FROM mytable m;
But you can then use the special syntax above to rewrite that as:
SELECT m.myinterval_nosecs FROM mytable m;
Note that since myinterval_nosecs is a function you cannot omit the m. at the beginning. This is because the query planner will rewrite the query in the former syntax and will not guess as to which relation you mean to run it against.
oracle has 'DESCRIBE' to get all the details of the table like wise does t/sql has any thing.
SQL Server has sp_help/sp_helptext
MySQL has describe
Sql-Server's sp_help is about as close as you get for something built-in. Remeber to put the tablename in as a parameter...:-)
EXEC sp_help 'mytable'
If you're in ssms, you can r-click your query window and opt to output results to text -- it's a little easier to read the output.
ms-help://MS.SQLCC.v10/MS.SQLSVR.v10.en/s10de_6tsql/html/913cd5d4-39a3-4a4b-a926-75ed32878884.htm
Also -- you can write your own using the system tables (sys.objects, sys.columns, ...) I think 'DESCRIBE' just gives you column name, nullable, and type... so not nearly as much as sp_help provides.
SELECT * FROM sysobjects WHERE parent_obj = (SELECT id FROM sysobjects WHERE name = 'table_name') AND xtype='PK'
will show table details.
SELECT * FROM sys.Tables
will list all tables
There is no describe equivalent.
you might find this searching for MSSQL instead of T/SQL. Most people talking about Transact SQL are talking about stored procedures.
I have a query which uses a cursor to cycle through the results of a select statement.
The select statement in short selects all of the records from a mapping table I have. One of the columns is 'SourceTableName'.
I use this field to generate some dynamic SQL.
I am looking to add a parameter to my stored procedure wrapped around this, which will allow me to only create dynamic SQL for the 'SourceTableName' that I want - IF I pass in a 'SourceTableNameFilter'.
I am stuck with some logic which wraps my dynamic SQL.
IF #SourceTableNameFilter(SP parameter) = #SourceTableName(from mapping table)
BEGIN
Generate and execute some dynamic SQL based on the SourceTableName.
The problem is, I want this to either work on all tables that come back from a select against 'SourceTableName' BUT if a #SourceTableNameFilter parameter is present and not null - then only generate dynamic SQL for any rows in the cursor which match my filter parameter.
Is there a way for me to accomplish this with an IF statement without copying the logic inside the IF/ELSE twice?
FETCH NEXT FROM TABLECUR INTO #SourceTableName
,#SourceInColumn
,#SourceOutColumn
,#TargetTableName
,#TargetLookupColumn
,#TargetLookupResultColumn
,#MappingTableID
WHILE (##fetch_status <> -1)
BEGIN
IF (##fetch_status <> -2)
BEGIN
IF (#SourceTableName = #SourceTableNameFilter)
--GENERATE DYNAMIC SQL
ELSE
--GENERATE DYNAMIC SQL FOR ALL RECORDS
The generate dynamic SQL string is the same in both the if and the else, any way to change the conditions so that I'm not duplicating the dynamic SQL generation and to not generate dynamic SQL when the #SourceTableName != #SourceTableNameFilter?
Thank you
Consider adding this logic to the cursor definition, rather than having that logic within the processing of each cursor record.
So if the cursor is normally:
DECLARE MY_CURSOR Cursor FOR
SELECT SourceTableName, SourceInColumn, SourceOutColumn
,TargetTableName, TargetLookupColumn
,TargetLookupResultColumn, MappingTableID
FROM MappingTable
--get source tables when filter is specified; otherwise get all
WHERE (SourceTableName = #SourceTableNameFilter) OR (LEN(ISNULL(SourceTableNameFilter,'')=0)
Now you can execute your business logic within the cursor without having to detect the filtered table or not. The cursor is loaded with the records you need to care about. It sounds, from the question, that the business logic is the same, no matter if the filter was passed in or not. If this is incorrect, or if it doesn't satisfy your requirement, please comment.
Knowing nothing about the dynamic sql you're building, I'd recommend doing something along the lines of:
SET #DynamicCommand = '<whatever, first part>'
+ isnull(#SourceTableNameFilter
,'<no special action, perhaps just empty string>'
,'<add conditional text dependent upon contents of #SourceTableNameFilter>')
+ '<whatever, second part>'