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.
Related
I'm working with a huge Firebird database where tables have completely unreadable names like WTF$RANDOM_ABBREVIATION_6792 or RPG$RANDOM_ABBREVIATION_5462 where columns have names like "rid9312", "1NUM5", "2NUM4", "RNAME8".
I need to set them global aliases to be able to use them as a full-length table names like Document and column names like
Document.CreationDate instead of xecblob.DDATE4
or
TempDoc.MovingOrderID instead of TMP$LINKED_DOC_6101.DID6101
Altering the database, or a table, or a column might be a big problem because the records might be counted by millions and tens of millions, and more over that, a major part of the Delphi-written front-end for the database is bound to the table names and column names.
Is there a way to do that somehow?
The closest thing there is to a "global alias" is to create views. For example:
create view document
as
select
DDATE4 as creationdate
-- , other columns...
from xecblob;
or
create view document (creationdate /*, other column aliases... */)
as
select
DDATE4
-- , other columns...
from xecblob;
(personally, I find the first variant more readable)
This does require altering the database, but there is no real cost associated with that (it doesn't matter if the table contains no, one, thousands or millions of records).
I have schema1 in database1. I want to move all the functions of schema1 to schema2 which is present in database2. I have restored backup file of database1 into database2. And changed the schema name. The schema name for function call automatically got changed. But within function definition the schema name is not changed. for ex:
CREATE OR REPLACE FUNCTION schema2.execute(..)
BEGIN
select schema1."VALIDATE_SESSION"(....)
end
How can I change "schema1" to "schema2" automatically?
I have tried to store current schema name in variable and append it to table. But calling current_schema() returns "public". How to get current schema created by user? Because every time I need to change the schema name while generating script.
The essential detail that is missing in your dummy function are the single quotes (or dollar-quotes, all the same) around the function body. Meaning, function bodies are saved as strings. See:
What are '$$' used for in PL/pgSQL
To contrast, consider a reference to a table (or more verbosely: schema.table(column)) in a FK constraint. Object names are resolved to the internal OID of the table (and a column number) at creation time. "Early binding". When names (including schema names) are changed later, that has no effect on the FK at all. Feels like involved names are changed dynamically. But really, actual names just don't matter after the object has been created. So you can rename schemas all day without side effect for the FK.
Names in a function body are stored as strings and interpreted at call time. "Late binding". Those names are not changed dynamically.
Meaning, you'll have to actually edit all function bodies including a hard-coded schema name. A possible alternative is to rely on the search_path instead and not use schema names in function bodies to begin with. There are various. See:
How does the search_path influence identifier resolution and the "current schema"
But that's not always acceptable.
You could hack the dump. Or use sting manipulation inside Postgres to update affected function bodies. Find affected functions with a meta-query like:
SELECT *
FROM pg_catalog.pg_proc
WHERE prosrc ~ '\mschema1\M'; -- not bullet-proof!
Either way, be wary of false matches if the schema name can be part of other strings or pop up as column name etc. And dynamic SQL can concatenate strings in arbitrary ways. If you have such evil trickery in your functions, you need to deal with it appropriately.
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 :
It seems PostgreSQL does not allow to create a database table named 'user'. But MySQL will allow to create such a table.
Is that because it is a key word? But Hibernate cannot identify any issue (even if we set the PostgreSQLDialect).
user is a reserved word and it's usually not a good idea use reserved words for identifiers (tables, columns).
If you insist on doing that you have to put the table name in double quotes:
create table "user" (...);
But then you always need to use double quotes when referencing the table. Additionally the table name is then case-sensitive. "user" is a different table name than "User".
If you want to save yourself a lot of trouble use a different name. users, user_account, ...
More details on quoted identifiers can be found in the manual: http://www.postgresql.org/docs/current/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
It is possible to specify tablename with JPA with next syntax:
#Table(name="\"user\"")
We had this same issue time ago, and we just changed the table name from user to app_user. Due to the use of Hibernate/JPA. We thought it would be easier this way.
Hope this little fix will help someone else.
You can create a table user in a schema other than public.
The example:
CREATE SCHEMA my_schema;
CREATE TABLE my_schema.user(...);
Trailing underscore
The SQL standard explicitly promises to never use a trailing underscore in any keyword or reserved word.
So, to avoid conflicts with any of the over a thousand keywords and reserved words used by various database engines, I name all my database identifiers with a trailing underscore. (Yes, really, over a thousand keywords reserved — I counted them.)
Change this:
CREATE TABLE user ( … ) ;
… to this:
CREATE TABLE user_ ( … ) ;
I do this as a habit for all database names: schemas, tables, columns, indexes, etc.
As an extra benefit, this practice makes quite clear in documentation, email, and such when referring to a programming language variable named user versus the database column user_. Anything with a trailing underscore is obviously from the database side.
I have to display a column name from a select query from table, e,g, 'Column 1' is stored in table table1, I want to display 'Column 1' as column name. I cannot hardcode 'Column 1' as it might be unknown when the code is developed.
Column 1 Column 2
a b
Any idea?
Update
It allows user to define column name.
It has to generate via T SQL
Add alias as a separate column or use dynamic SQL
This doesn't make sense because doing you should know what the column is called: you don't store information about columns and build queries on your own metadata
IF you don't know the name of the column at design time, then use a resource file or similar in the presentation layer to hold the value that you will display as the label for column1. It should be noted, however, you are going to have a very hard time writing any code if you don't know the names of the columns in your database, unless you are select * on everything.
Column names are fairly restricted and should be named with the SQL admin and application developer as the user of the names. It is not the intent of a column name to be descriptor for the end user interface.
Select dbColumn1 as [Customer Name] from tableMain
Even that is not a good practice and then user input is part of the TSQL and you are opening yourself up to SQL injection attacks and it is just not very good control on you query. A better practice is to pass parameters.