I need to format my SELECT queries on a text column. How may I do it without expliciting inserting it together with the query?
Do i use a rule in this case? I have tried creating a rule on the tables' column but apparently it won't work.
create or replace rule t_format AS ON SELECT TO site_ss_last_entry2
DO INSTEAD
select internet_date(site_ss.last_entry2) from site_ss;
Just create a VIEW and SELECT from this VIEW to get what you're looking for.
Related
I'm a real beginner when it comes to SQL and I'm currently trying to build a database using postgres. I have a lot of data I want to put into my database in JSON files, but I have trouble converting it into tables. The JSON is nested and contains many variables, but the behavior of jsonb_populate_record allows me to ignore the structure I don't want to deal with right now. So far I have:
CREATE TABLE raw (records JSONB);
COPY raw from 'home/myuser/mydocuments/mydata/data.txt'
create type jsonb_type as (time text, id numeric);
create table test as (
select jsonb_populate_record(null::jsonb_type, raw.records) from raw;
When running the select statement only (without the create table) the data looks great in the GUI I use (DBeaver). However it does not seem to be an actual table as I cannot run select statements like
select time from test;
or similar. The column in my table 'test' also is called 'jsonb_populate_record(jsonb_type)' in the GUI, so something seems to be going wrong there. I do not know how to fix it, I've read about people using lateral joins when using json_populate_record, but due to my limited SQL knowledge I can't understand or replicate what they are doing.
jsonb_populate_record() returns a single column (which is a record).
If you want to get multiple columns, you need to expand the record:
create table test
as
select (jsonb_populate_record(null::jsonb_type, raw.records)).*
from raw;
A "record" is a a data type (that's why you need create type to create one) but one that can contain multiple fields. So if you have a column in a table (or a result) that column in turn contains the fields of that record type. The * then expands the fields in that record.
In output I want to select all columns except two columns from a table in q/kdb historical database.
I tried running below query but it does not work on hdb.
delete colid,coltime from table where date=.z.d-1
but it is failing with below error
ERROR: 'par
(trying to update a physically partitioned table)
I referred https://code.kx.com/wiki/Cookbook/ProgrammingIdioms#How_do_I_select_all_the_columns_of_a_table_except_one.3F but no help.
How can we display all columns except for two in kdb historical database?
The reason you are getting par error is due to the fact that it is a partitioned table.
The error is documented here
trying to update a partitioned table
You cannot directly update, delete anything on a partitioned table ( there is a separate db maintenance script for that)
The query you have used as fix is basically selecting the data first in-memory (temporarily) and then deleting the columns, hence it is working.
delete colid,coltime from select from table where date=.z.d-1
You can try the following functional form :
c:cols[t] except `p
?[t;enlist(=;`date;2015.01.01) ;0b;c!c]
Could try a functional select:
?[table;enlist(=;`date;.z.d);0b;{x!x}cols[table]except`colid`coltime]
Here the last argument is a dictionary of column name to column title, which tells the query what to extract. Instead of deleting the columns you specified this selects all but those two, which is the same query more or less.
To see what the functional form of a query is you can run something like:
parse"select colid,coltime from table where date=.z.d"
And it will output the arguments to the functional select.
You can read more on functional selects at code.kx.com.
Only select queries work on partitioned tables, which you resolved by structuring your query where you first selected the table into memory, then deleted the columns you did not want.
If you have a large number of columns and don't want to create a bulky select query you could use a functional select.
?[table;();0b;{x!x}((cols table) except `colid`coltime)]
And show all columns except a subset of columns. The column clause expects a dictionary hence I am using the function {x!x} to convert my list to a dictionary. See more information here
https://code.kx.com/q/ref/funsql/
As nyi mentioned, if you want to permanently delete columns from an historical database you can use the deleteCol function in the dbmaint tools https://github.com/KxSystems/kdb/blob/master/utils/dbmaint.md
I am a novice at Firebird SQL.
Can anyone advise how I specify the order of field name in Firebird? If I change the name of the header, then it places that field at the end.
In another situation the field names appear differently in Excel that they do in the preview. (Can't see any particular pattern, not even aphabetical or alphabetical per table).
Any hints are appreciated.
I understand your question as you want to change the fields order in a table, permanently.
For that, Firebird FAQ gives this DDL-statement:
ALTER TABLE table_name ALTER field_name POSITION new_position;
Positions are numbered from one. If you wish to exchange two fields, make sure you run the statement for both of them.
If you want to change the fields order temporary, e.g. in a query, you can obviously just define the fields order in the select statement. But I think, this is one of the first things a SQL novice learns.
By SQL
ALTER TABLE TABLE_NAME ALTER COLUMN FIELD_NAME POSITION x;
http://firebirdsql.org/refdocs/langrefupd20-alter-table.html#langrefupd20-at-position
Far as I know, there is no option to automatically arrange the fields. But you may use your preferred tools like Flame Robin, IBExpert etc. to do this manually. They have this functionality.
For example Flame Robin :
I've noticed that while I can use %dictionary.compiledclass to get a table with schema names and table names, which allow querying for their existence, I cannot do the same for columns. I have yet to find the command that allows verifying whether a column exists or not, or retrieving numerous column names using LIKE "prefix%".
Is there even such a thing? Or an alternative?
You can use %Dictionary.CompiledProperty table and SqlFieldName column of that table.
For example to find out tables that have column 'ColumnName' you can use this query:
select parent->SqlTableName
from %dictionary.compiledproperty
where SqlFieldName='ColumnName'
Execute this Query :
select * from %dictionary.compiledproperty Where parent='TableName' and SqlFieldName='ColumnName'
Check Row Count value ,0 not exist
My current query looks something like this:
SELECT SUBSTR(name,1,1), COUNT(*) FROM files GROUP BY SUBSTR(name,1,1)
But it's taking a pretty long time just to do counts on a table that's already indexed by the name column. I saw from this question that some engines might not use indexes correctly for the SUBSTR function, and in fact, sqlite will not use indexes for SUBSTR(string,1,1).
Is there any other approach that would utilize the index and net me some faster queries?
One strategy that is consistent with your access pattern is to add a new indexed column "first_letter" to your table. Use a trigger on to set the value on insert and update. Then your query is a simple group by first_letter.
Another strategy is to create a shadow table which contains an aggregation of the mother table. This isn't easy because it is your job as developer to keep the shadow table consistent with the mother table. Every delete, update or insert in table files needs to be accompanied by a change in the shadow table.
Databases like Oracle have support for materialized views to achieve this automatically but sqlite doesn't.