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引自MSDN的Select语法结构(为了方便自己查找:))

2009-09-24 19:37 573 查看
引自MSDN：http://msdn.microsoft.com/en-us/library/aa656402.aspx

Select Statement Syntax

SelectStatement

=

select
Parameters

Parameters

[[
FindOptions 
]
[
FieldList 
 from]]
TableBufferVariable 
[
IndexClause 
]
[
Options 
]
[
WhereClause 
]
[
JoinClause 
]


FindOptions

=

crossCompany
| 
reverse
| 
firstFast
| [
firstOnly
| 
firstOnly10
| 
firstOnly100
| 
firstOnly1000
] | 
forUpdate
| 
noFetch
| [
forcePlaceholders
| 
forceLiterals
] | 
forceselectorder
| 
forceNestedLoop
| 
repeatableRead


FieldList

=

Field 
{ ,
Field 
}
| 
*


Field

=

Aggregate 
(
FieldIdentifier 
) |
FieldIdentifier

Aggregate

=

sum
| 
avg
| 
minof
| 
maxof
| 
count


Options

=

[order by
, 
group by ,
FieldIdentifier
 [asc
| 
desc]{ ,
FieldIdentifier
 [asc
| 
desc]}]
| 
[
IndexClause
]


IndexClause

=

index
IndexName | 
indexhint
IndexName

WhereClause

=

where
Expression

JoinClause

=

[
exists
| 
notexists
| 
outer
] 
join
Parameters


Keywords Used in the Select Syntax

Keyword

Description

Example

asc

An option on the 
order by
or 
group by
clause. The sorting is ascending. (Sort is ascending by default.)

select * from custTable


order by Name asc;


avg

Returns the average of the fields.

CustTable custTable;


;


select avg(value) from custTable;


print custTable.value;


count

Returns the number of records.

CustTable xCT;


int64 iCountRows; ;


Select COUNT(RecID) from xCT;


iCountRows = xCT.RecID;


crossCompany

Returns data for all companies that the user is authorized to read from. (A 
container
can be added to reduce the number of companies involved.)

CustTable custTable;


container conCompanies = ['dat','dmo'];


;


select crossCompany :conCompanies


* from custTable;


desc

An option on the 
order by
or 
group by
clause. The sorting is descending.

select * from custTable


order by Name desc;


exists

A method that returns a Boolean value and a 
join
clause.

while select AccountNum, Name from custTable


order by AccountNum


    exists join* from ctr


    where(ctr.AccountNum ==


custTable.AccountNum)


firstFast

A priority hint. The first row appears more quickly but the total return time for this option might be slower. The 
firstFast
hint is automatically issued from all forms, but is rarely used directly from X++.

select firstFast custTable


order by AccountNum;


firstOnly

Speeds up the fetch. Instructs MorphX to fetch only the first record.

static InventTable find(


ItemId   itemId,


boolean  update = false)


{


InventTable inventTable;


;


inventTable.selectForUpdate


(update);


if (itemId)


{


select firstonly inventTable


            indexhint ItemIdx


            whereinventTable.itemId


== itemId;


   }


return inventTable;


}


firstOnly10

Same as firstOnly, except returns 10 rows instead of one.



firstOnly100

Same as firstOnly, except returns 100 rows instead of one.



firstOnly1000

Same as firstOnly, except returns 1000 rows instead of one.



forceLiterals


Note 
You are advised not to use the forceLiterals keyword in X++ 
select
 statements, because it could expose code to an SQL injection security threat.

forceLiterals instructs the kernel to reveal the actual values that are used in 
where
 clauses to the Microsoft SQL Server database at the time of optimization.

forceLiterals and forcePlaceholders are mutually exclusive.



forceNestedLoop

Forces the Microsoft SQL Server database to use a nested-loop algorithm to process a particular SQL statement containing a joinalgorithm. This means that a record from the first table is fetched before any records from the second table are fetched. Typically, other joinalgorithms, such as hash-joins and merge-joins, would be considered. This keyword is often combined with the forceSelectOrder keyword.

while select forceSelectOrder


forceNestedLoop inventTransThis


    indexhint TransIdIdx


    whereinventTransThis.InventTransId


== inventTrans.InventTransId


&& inventTransThis.StatusIssue


<= StatusIssue::ReservOrdered


forcePlaceholders

Instructs the kernel not to reveal the actual values used in 
where
 clauses to the SQL Server database at the time of optimization. This is the default in all statements that are not 
join
 statements.

The advantage of using this keyword is that the kernel can reuse the access plan for other similar statements with other search values. The disadvantage is that the access plan is computed without taking into consideration that data distribution might not be even. The access plan is an on-average access plan.

forcePlaceholders and forceLiterals are mutually exclusive.

static void forcePlaceHoldersExample(Args _args)


{


SalesTable salesTable;


SalesLine  salesLine;


;


while select forcePlaceholders salesLine


        joinsalesTable


           wheresalesTable.SalesId ==


salesLine.SalesId


&& salesTable.SalesId == '10'


{


//more code


   }


}


forceSelectOrder

Forces the SQL Server database to access the tables in a joinin the specified order. If two tables are joined, the first table in the statement is always accessed first. This keyword is often combined with the forceNestedLoop keyword.

display ForecastHasPurch hasForecastPurch()


{


ForecastPurch   forecastPurch;


InventDim       inventDim;


;


select firstOnly forcePlaceholders


forceSelectOrder recId


from forecastPurch


        indexhint ItemIdx


        whereforecastPurch.itemId  == this.itemId


    exists joininventDim


        indexhint DimIdIdx


        whereinventDim.inventDimId ==


forecastPurch.inventDimId


&& inventDim.configId == this.configId;


return forecastPurch.recId;


}


forUpdate

Selects records exclusively for update. Depending on the underlying database, the records may be locked for other users.

ttsBegin;


while select forUpdate ledgerJournalTrans


    indexhint NumVoucherIdx


    whereledgerJournalTrans.journalNum == 


_journalNum &&


ledgerJournalTrans.voucher == _voucher


{


ledgerJournalTrans.doDelete();


counter++;


}


if (counter


&& ledgerJournalTable.journalType


!= LedgerJournalType::Periodic)


{


NumberSeq::release(


ledgerJournalTable.voucherSeries,


_voucher);


}


ttsCommit;


group by

Instructs the database to group selected records by fields.

CustTable custTable;


;


while select sum(CreditMax) from custTable


group by CustGroup


{


print custTable.CustGroup, " ",custTable.CreditMax;


}


index

Instructs the database to sort the selected records as defined by the index.

CustTable custTable;


;


while select AccountNum, Name from custTable


    indexAccountIdx


{


print custTable.AccountNum, " ", custTable.Name;


}


indexhint

Gives the database a hint to use this indexto sort the selected records as defined by the index. The database can ignore the hint.


Note 
A wrong indexhint can have a big performance impact. Index hints should only be applied to SQL statements that do not have dynamic 
where
 clauses or 
order by
 clauses, and wherethe effect of the hint can be verified.

while select forUpdate ledgerJournalTrans


    indexhint NumVoucherIdx


    whereledgerJournalTrans.journalNum 


== _journalNum


join

Used to jointables on a column that is common to both tables.

Reduces the number of SQL statements that are needed if you want to loop through a table and update transactions in a related table.

For example, if you process 500 records in a table, and want to update related records in another table, and use a nested 
while select
 to do this, there will be 501 trips to the database. If you use a join, there will be a single trip to the database.

while select ledgerTable


    joinledgerTrans


        whereledgerTrans.accountNum ==


ledgerTable.accountNum


{


amountMST += ledgerTrans.amountMST;


   }


maxof

Returns the maximum of the fields.

CustTable custTable;


;


select maxof(CreditMax) from custTable;


minof

Returns the minimum of the fields.

CustTable custTable;


;


select minof(CreditMax) from custTable;


noFetch

Indicates that no records are to be fetched at present. This is typically used when the result of the select is passed on to another application object, for example, a query that performs the actual fetch.

select noFetch custTable


order by AccountNum


notExists

Chosen only if there are no posts.

while select AccountNum, Name from custTable


order by AccountNum


    notExists join* from ctr


    where(ctr.AccountNum ==


  custTable.AccountNum)


optimisticLock

Forces a statement to run with Optimistic Concurrency Control even if a different value is set on the table.

For more information, see Optimistic Concurrency Control.

select optimisticLock custTable


    wherecustTable.AccountNum > '1000'


order by

Instructs the database to sort the selected records by fields in the 
order by
 list.

select * from custTable


order by accountNum desc


    wherecustTable.AccountNum > "100";


outer

outer join. Can typically display all rows that both do and do not meet the conditions. An outer join can display all non-matching rows from either the first-named table or second-named table, or from both tables together.

while select AccountNum, Name


from custTable


order by AccountNum


    outer join* from ctr


    where(ctr.AccountNum == custTable.AccountNum)


pessimisticLock

Forces a statement to run with Pessimistic Concurrency Control even if a different value is set on the table.

For more information, see Optimistic Concurrency Control.

select pessimisticLock custTable


    wherecustTable.AccountNum > '1000'


repeatableRead

Specifies that no other transactions can modify data that has been read by logic inside the current transaction, until after the current transaction completes.

An explicit transaction completes at either ttsAbort or at the outermost ttsCommit.

For a stand-alone select statement, the transaction duration is the duration of the select command. However, the database sometimes enforces the equivalent of repeatableRead in individual select statements even without this keyword appearing in your X++ code (depending on how the database decides to scan the tables).

For more information, see the documentation for the underlying relational database product.

reverse

Records are returned in reverse order.

select reverse custTable


order by AccountNum;


sum

Returns the sum of the fields. Can be used to sum all accounts, order lines, and so on.

CustTable custTable;


;


select sum(CreditMax) from custTable;



                                            

                                        

                        
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