BigQuery supports the following notation for SQL:
select_list:
{ select_all | select_expression } [, ...]
select_all:
[ expression. ]*
[ EXCEPT ( column_name [, ...] ) ]
[ REPLACE ( expression [ AS ] column_name [, ...] ) ]
Meaning something like the following can be done:
SELECT * EXCEPT (id, socialSecurity)
And some other small things.
Do any databases support this? I find the EXCEPT clause useful, and although I know how to use the REPLACE I've never found an actual practical use case for that ever. Are there ever any practical uses of that (i.e., aside from made up examples in the docs)?
Related
I have just come across this syntax for defining an inline view...
SELECT myAlias, myAlias1 FROM ( SELECT myCol, myCol1 FROM myTable ) V( myAlias, myAlias1)
I can see what the V is doing, but what is this called and where is it documented? And why would I ever want to do this when I can just define the aliases inside the inline view?
Googling seems not to be working because V is not a word!
V is just another alias - it's the alias for the whole subquery, not for an individual column.
See the derived table line from the syntax for FROM:
| derived_table [ [ AS ] table_alias ] [ ( column_alias [ ,...n ] ) ]
V is the table_alias.
when I can just define the aliases inside the inline view
Yes, you often can. But sometimes you're building a complex query with lots of nesting in the individual column expressions, and it's easier to place all of the names (the table_alias and column_aliases) that will be exposed to the remaining parts of the query in one place.
Below is the synopsis of SELECT from the PostgreSQL documentation. It seems to me that sometimes we write <expression> AS <name> and sometimes it's <name> AS <expression>. In ordinary English, I tend to think <expression> AS <name> is much more common (e.g. "Address her as. Doctor Smith, please., and I'm having trouble understanding how to think about <name> AS <expression>.
How can we distinguish between where to use <name> AS <expression> and <expression> as <name>?
What are minimal obvious examples of each?
Are there parallels of each kind in ordinary language, which would make it intuitively obvious when to use what?
[ WITH [ RECURSIVE ] with_query [, ...] ]
SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
* | expression [ [ AS ] output_name ] [, ...]
[ FROM from_item [, ...] ]
[ WHERE condition ]
[ GROUP BY expression [, ...] ]
[ HAVING condition [, ...] ]
[ WINDOW window_name AS ( window_definition ) [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] select ]
[ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ LIMIT { count | ALL } ]
[ OFFSET start [ ROW | ROWS ] ]
[ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]
[ FOR { UPDATE | SHARE } [ OF table_name [, ...] ] [ NOWAIT ] [...] ]
where from_item can be one of:
[ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
( select ) [ AS ] alias [ ( column_alias [, ...] ) ]
with_query_name [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [, ...] | column_definition [, ...] ) ]
function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )
from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]
and with_query is:
with_query_name [ ( column_name [, ...] ) ] AS ( select | values | insert | update | delete )
TABLE [ ONLY ] table_name [ * ]
I like the question.
Here is how I see it and how I explain it to people, hope it helps:
Let's start with <expression> as <name>. The simplest analogy from real life is an abbreviation. It was created to make the code cleaner, easier to read and simply shorter. Let's imagine a scenario: we have data on all students from the Massachusetts Institute of Technology as well as Massachusetts Department of Motor Vehicles in our database and we want to find students that have speeding tickets and how much they have paid.
SELECT
government.SocialSecurityAdministration.FirstName,
government.SocialSecurityAdministration.LastName,
education.MasachusettsInstituteOfTechnology.Faculty
government.DepartmentOfMotorVehiclesTickets.TicketTotal,
government.SocialSecurityAdministration.SocialSecurityNumber
FROM
education.MasachusettsInstituteOfTechnology
INNER JOIN government.DepartmentOfMotorVehiclesTickets ON education.MasachusettsInstituteOfTechnology.SocialSecurityNumber = government.DepartmentOfMotorVehicles.SocialSecurityNumber
INNER JOIN government.SocialSecurityAdministration ON government.DepartmentOfMotorVehicles.SocialSecurityNumber = government.SocialSecurityAdministration.SocialSecurityNumber
Looks ugly, doesn't it? In real life, we've abbreviated the Massachusetts Institute of Technology to be MIT and the Department of Motor Vehicles to be DMV. I'm not aware of the official abbreviation for Social Security Administration (but we can come up with one) though we say SSN when we mean Social Security Number. Let's implement this idea:
SELECT
ssnAdm.FirstName,
ssnAdm.LastName,
ssnAdm.Faculty
dmv.TicketTotal,
ssnAdm.SocialSecurityNumber AS ssn
FROM
education.MasachusettsInstituteOfTechnology AS mit
INNER JOIN government.DepartmentOfMotorVehiclesTickets AS dmv ON mit.SocialSecurityNumber = dmv.SocialSecurityNumber
INNER JOIN government.SocialSecurityAdministration AS ssAdm ON dmv.SocialSecurityNumber = dmv.SocialSecurityNumber
Looks better now, doesn't it?
Now to the <name> as <expression> portion of it. This is done to simplify the code as well as some performance optimizations but let's focus on simplification for now. Using the same example I've used above, you might want to get/ask the following: "For every MIT student that has received a ticket I need to know the last 4 digits of their SSN, their last name, the amount of money in their bank account and their last VISA transaction amount". Yes, you work for CIA.
Let's write it:
SELECT
RIGHT(4,ts.ssn) as LastFourDigitsSsn,
ts.LastName,
bad.TotalAmount,
ISNULL(visa.TransactionAmt,'Student uses MasterCard') AS VisaTransaction
FROM
(SELECT
ssnAdm.FirstName,
ssnAdm.LastName,
ssnAdm.Faculty
dmv.TicketTotal,
ssnAdm.SocialSecurityNumber AS ssn
FROM
education.MasachusettsInstituteOfTechnology AS mit
INNER JOIN government.DepartmentOfMotorVehiclesTickets AS dmv ON mit.SocialSecurityNumber = dmv.SocialSecurityNumber
INNER JOIN government.SocialSecurityAdministration AS ssAdm ON dmv.SocialSecurityNumber = dmv.SocialSecurityNumber
) AS ts
INNER JOIN business.BankAccountsData AS bad ON ts.ssn = bad.SocialSecurityNumber
OUTER APPLY (SELECT TOP 1 TransactionAmt FROM business.VisaProcessingData vpd WHERE vpd.BankAccountID = bad.ID ORDER BY TransactionDateTime DESC) as visa
Well, looks ugly again. But what if we simplify it a bit and express certain things outside of the actual statement? That's when <name> as <expression> comes in. Let's do it:
WITH MitTicketedStudents AS (
SELECT
ssnAdm.LastName,
ssnAdm.SocialSecurityNumber as ssn,
RIGHT(4,ssnAdm.SocialSecurityNumber) as LastFourDigitsSsn
FROM
education.MasachusettsInstituteOfTechnology AS mit
INNER JOIN government.DepartmentOfMotorVehiclesTickets AS dmv ON mit.SocialSecurityNumber = dmv.SocialSecurityNumber
INNER JOIN government.SocialSecurityAdministration AS ssAdm ON dmv.SocialSecurityNumber = dmv.SocialSecurityNumber
),
LatestVisaTransactions AS (
SELECT DISTINCT
BankAccountID,
FIRST_VALUE(TransactionAmt) OVER (PARTITION BY BankAccountId ORDER BY TransactionDateTime DESC) as TransactionAmt
FROM
business.VisaProcessingData
)
-- And let's use our expressions now
SELECT
mts.LastFourDigitsSsn,
mts.LastName,
bad.TotalAmount,
ISNULL(lvt.TransactionAmt,'Student uses MasterCard') AS VisaTransaction
FROM
MitTicketedStudents mts
INNER JOIN business.BankAccountsData AS bad ON mts.ssn = bad.SocialSecurityNumber
LEFT OUTER JOIN LatestVisaTransactions lvt ON bad.ID = lvt.BankAccountID;
Looks better, doesn't it?
Conclusion: when you want to separate code you use <name> as <expression>, when you want to give something an alias to simplify code you use <expression> as <name>.
What matters is where it appears.
mytable:
mycolumn myothercolumn
----------------------
1 a
2 b
SELECT myrow.mycolumn * 2 AS mylabel
FROM (SELECT * FROM mytable) AS myrow
WHERE myrow.mycolumn > 1
mylabel
-------
4
In SELECT, we refer to the value of an expression AS some output column name ("column alias"). In FROM, we refer to (a typical row of) the value of a table expression AS some name ("table alias", "correlation name").
(It turns out that because of details of the grammar typos are less problematic if we use AS in SELECT clauses but don't use AS in FROM clauses.)
There are other uses of AS. The context also determines what they mean, and they also correspond to using using a name to refer to something.
In technical contexts it turns out not to be helpful to try to make sense of what something means based on the everyday meanings of technical terms, including making sense of what a thing is based on its name. The SQL language designers [sic] didn't choose to always have either <expression> AS <name> or <name> AS <expression>. That is just how it is. That is just how you write stuff to get your program to do stuff to stuff. (Accepted but more modern principles of computer language design do suggest more regular notations.)
I am trying to use CONTAINSTABLE with FORMSOF and searching for prefixes using the asterisk. Is this possible, and if so what is the correct syntax?
My (wrong) attempt is:
CONTAINSTABLE( abc.Table, ColumnName, 'FORMSOF( THESAURUS, "wine*" OR "vine*" )')
What do I need to change to make this valid?
CONTAINSTABLE Doesnt take table name as parameter, it will only search on columns
It should be like:
CONTAINSTABLE(ColumnName, 'FORMSOF( THESAURUS, "wine*" OR "vine*" )')
Not possible in one term. From the docs:
<simple_term> ::=
{ word | "phrase" }
<prefix term> ::=
{ "word*" | "phrase*" }
<generation_term> ::=
FORMSOF ( { INFLECTIONAL | THESAURUS } , <simple_term> [ ,...n ] )
https://learn.microsoft.com/en-us/sql/relational-databases/system-functions/containstable-transact-sql?view=sql-server-ver15
If it was combined into one term it could be quite expensive, because you're asking the DB to find all words with the substring and then find all similar words to those. In your above example it would have to do that for both wine* and vine*. Ranking might be interesting too.
One workaround is to search twice, once using prefix and once using the thesaurus, then combine the results using your own ranking approach.
CONTAINSTABLE Can take table name as parameter
CONTAINSTABLE
( table , { column_name | ( column_list ) | * } , ' <contains_search_condition> '
[ , LANGUAGE language_term]
[ , top_n_by_rank ]
)
See MS Docs
I am pretty novice in writing SQL but would like to get better. One of the things that I have never really understood is how to interpret the construct syntax for any give object. Here is an example of OPENROWSET definition taken from https://msdn.microsoft.com/en-us/library/ms190312.aspx. I understand the pipe "|" represents "OR" but not sure about the other tags. Is there a good place to learn how to interpret this?
OPENROWSET
( { 'provider_name' , { 'datasource' ; 'user_id' ; 'password'
| 'provider_string' }
, { [ catalog. ] [ schema. ] object
| 'query'
}
| BULK 'data_file' ,
{ FORMATFILE = 'format_file_path' [ <bulk_options> ]
| SINGLE_BLOB | SINGLE_CLOB | SINGLE_NCLOB }
} )
<bulk_options> ::=
[ , CODEPAGE = { 'ACP' | 'OEM' | 'RAW' | 'code_page' } ]
[ , ERRORFILE = 'file_name' ]
[ , FIRSTROW = first_row ]
[ , LASTROW = last_row ]
[ , MAXERRORS = maximum_errors ]
[ , ROWS_PER_BATCH = rows_per_batch ]
[ , ORDER ( { column [ ASC | DESC ] } [ ,...n ] ) [ UNIQUE ]
On every page of Microsoft Docs (previously MSDN) that refers to SQL Server (even about OPENROWSET) there is a link called Transact-SQL Syntax Conventions (#Ghost post it in a comment)
That link will guide you to the page with explanation of SQL Syntax Conventions that you seek.
I think the easiest way to understand this syntax is visual Railroad Diagram.
How to use it:
Get syntax from documentation
Paste to Grammar Translator written by Colin Daley
You may need to manually correct some errors (like missing brackets, '')
Click Generate Railroad Diagram
Learn by moving from start to end
Image generated using: http://bottlecaps.de/rr/ui
You can also search for Railroad Diagrams for SQL Server.
SQL Server CREATE TABLE syntax diagrams
Most important syntax:
Optional items are enclosed in square brackets
Groups of expressions are enclosed in curly braces
A '|' is a binary operator meaning 'or'.
I have a example query(fully modified) as below:
with projects as (
select * from projectdetails
)
select * from projects
when I run the above query, it is running fine.
But when i put one more select query..it is throwing error.
select * from
(
with projects as (
select * from projectdetails
)
select * from projects
)
Error: Incorrect syntax near the keyword 'with'. If this statement is
a common table expression, an xmlnamespaces clause or a change
tracking context clause, the previous statement must be terminated
with a semicolon.
The same query runs fine in Oracle but not in SQL server.
SQL Server and Oracle have different syntax requirements for common table expressions.
In Oracle, these can come before any SELECT. In SQL Server, they need to come at the beginning of the query. Hence, you cannot have a subquery with WITH in it.
Usually, you can just move the WITH statement before the first SELECT and the query will work in both databases.
It doesn't matter what runs on Oracle, see supported SQL Server SELECT syntax
Simplified:
[ WITH { [ XMLNAMESPACES ,] [ <common_table_expression> ] } ]
SELECT select_list [ INTO new_table ]
[ FROM table_source ] [ WHERE search_condition ]
[ GROUP BY group_by_expression ]
[ HAVING search_condition ]
[ ORDER BY order_expression [ ASC | DESC ] ]
Full:
<SELECT statement> ::=
[ WITH { [ XMLNAMESPACES ,] [ <common_table_expression> [,...n] ] } ]
<query_expression>
[ ORDER BY { order_by_expression | column_position [ ASC | DESC ] }
[ ,...n ] ]
[ <FOR Clause>]
[ OPTION ( <query_hint> [ ,...n ] ) ]
<query_expression> ::=
{ <query_specification> | ( <query_expression> ) }
[ { UNION [ ALL ] | EXCEPT | INTERSECT }
<query_specification> | ( <query_expression> ) [...n ] ]
<query_specification> ::=
SELECT [ ALL | DISTINCT ]
[TOP ( expression ) [PERCENT] [ WITH TIES ] ]
< select_list >
[ INTO new_table ]
[ FROM { <table_source> } [ ,...n ] ]
[ WHERE <search_condition> ]
[ <GROUP BY> ]
[ HAVING < search_condition > ]
If you don't know how to read this syntax directly you can generate Railroad Diagrams for every syntax definition from BOL examples below:
The query which you are trying to execute is called Common Table Expression and the the syntax which you are using is not the proper way of using it ie, you cannot use the WITH clause inside the select statement.
with projects as (
select * from projectdetails
)
select * from projects
The above query is fine and will work and the next query which you posted is neither correct and neither it is making sense as it is looking as if you are trying to do the same thing as above.
As other two answers speak about the syntax of CTE and their limitation, here is a way you would do this what you are trying to do, Multiple CTEs.
with projectdetails as (
select * from projectdetails
),projects AS
select * from projects
)
SELECT * FROM projects --<-- here you select from Projects or projectdetails