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 :
Related
I'm trying to organize my PosgtresSql tables according to the application components they correspond to. For example, tables related to 'story' such as 'story_contents', 'story_comments', 'story_layout': would it best to keep a simple '' naming convention as presented? Would there be any drawback to using a '.' instead of ''? ... or is there a best practice that I'm completely overlooking?
Short answer:
Sure, if you place the entire database/table/column name reference in quotes
Long answer:
In Postgres, and most other databases, the dot is used to separate database name from table name, and table name from column name. For example, if you had a database called MyDB, with a table called MyTable and column in that table MyCol, then you could write the following SELECT statement:
SELECT MyDB.MyTable.MyCol
FROM MyDB.MyTable
However, if your database, table, and/or column names themselves had dots in them, then doing a SELECT might not work. In this case, I believe you can escape the fully qualified name (or portion) with quotes. So, if you had a column called MyCol.Col1, you could do the following:
SELECT "MyDB.MyTable.MyCol.Col1"
FROM MyDB.MyTable
The comment by #vector seems to be pointing in the right direction (no pun intended), and you should lean towards using underscores or some other character to separate out your schema names, rather than using a dot.
Right now when I create a table and do a
select * from table
I always see the first insert rows first. I'd like to have my latest inserts displayed first. Is it possible to achieve with minimal performance impact?
I believe that Postgres uses an internal field called OID that can be sorted by. Try the following.
select *,OID from table order by OID desc;
There are some limitations to this approach as described in SQL, Postgres OIDs, What are they and why are they useful?
Apparently the OID sequence "does" wrap if it exceeds 4B 6. So in essence it's a global counter that can wrap. If it does wrap, some slowdown may start occurring when it's used and "searched" for unique values, etc.
See also https://wiki.postgresql.org/wiki/FAQ#What_is_an_OID.3F
NB - in more recent version of Postgres this could be deprecated ( https://www.postgresql.org/docs/8.4/static/runtime-config-compatible.html#GUC-DEFAULT-WITH-OIDS )
Although you should be able to create tables with OID even in the most recent version if done explicitly on table create as per https://www.postgresql.org/docs/9.5/static/sql-createtable.html
Although the behaviour you are observing in the CLI appears consistent, it isn't a standard and cannot be depended on. If you are regularly needing to manually see the most recently added rows on a specific table you could add a timestamp field or some other sortable field and perhaps even wrap the query into a stored function .. I guess the approach depends on your particular use case.
In a PostgreSQL db I'm working on, half of the tables have one particular column, always named the same, that is of type varchar(5). The size became a bit too restricting and I want to change it to varchar(10).
The number of tables in my particular case is actually very manageable to do it by hand. But I was wondering how one could script this with a query for larger dbs. It generally should be possible in just a few steps.
Identify all the tables in the schema, then (?) filter by condition if column present.
Create ALTER TABLE statements for each table found
I have some idea about how to write a query that identifies all tables in the schema. But I wouldn't know how to filter them. And if I didn't filter them, I assume the generated alter table statements would break.
Would be great if someone could share their knowledge on this.
Thanks to Abelisto for providing some guidance. Eventually, this is how I did it.
First, I created a query that in turn creates the ALTER TABLE statements. MyDB and MyColumn need to reflect actual values.
SELECT
'ALTER TABLE '||columns.table_name||' ALTER COLUMN '||MyColumn||' TYPE varchar(20);'
FROM
information_schema.columns
WHERE
columns.table_catalog = 'MyDB' AND
columns.table_schema = 'public' AND
columns.column_name = 'MyColumn';
Then it was just a matter of executing the output as a new query. All done.
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.
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.