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Select statement

  • Стаття

The select statement fetches or manipulates data from the database.

  • All select statements use a table variable to fetch records. This variable must be declared before a select statement can be run.

  • The select statement fetches only one record, or field. To fetch or traverse multiple records, you can use the next statement or the while select statement.

    • The next statement fetches the next record in the table. If no select statement precedes the next statement, an error occurs. If you use a next statement, don't use the firstOnly find option.
    • It's more appropriate to use a while select statement to traverse multiple records.

  • The results of a select statement are returned in a table buffer variable.

  • If you use a field list in the select statement, only those fields are available in the table variable.

Select example

The following example fetches all the columns in the first row of the CustTable table and prints the value in the AccountNum column of that row.

CustTable custTable;
select * from custTable;
info("AccountNum: " + custTable.AccountNum);

For more examples of data selection, see Select data.

Insert example

The following example inserts a new record into the CustTable table. The AccountNum column of the new record is set to 2000, and the CustGroup column is set to 1. Other fields in the record will be blank.

ttsBegin;
    CustTable custTable;
    custTable.initValue();
    custTable.AccountNum = '2000';
    custTable.CustGroup = '1';
    custTable.insert();
ttsCommit;

For more examples of data insertion, see Insert data.

Update example

The following example selects the CustTable table for update. Only records where the value of the AccountNum field equals 2000 are updated. Because there is no call to next, and this example doesn't use a select while statement, only one record is updated. The value of the CreditMax field is changed to 5000.

ttsBegin;
    CustTable custTable;
    select forUpdate custTable
        where custTable.AccountNum == '2000';
    custTable.CreditMax = 5000;
    custTable.update();
ttsCommit;

For more examples of data updates, see Update data.

Delete example

In the following example, all records in the CustTable table where the AccountNum field equals 2000 are deleted from the database. One record is deleted at a time.

ttsBegin;
    CustTable custTable;
    while select forUpdate CustTable
        where custTable.AccountNum == '2000'
    {
        custTable.delete();
    }
ttsCommit;

For more examples of data deletion, see Delete data.

Syntax of the select statement

The following symbols are used in the syntax:

  • [] – Brackets enclose an optional element.
  • {} – Braces enclose an element that can be included zero or more times.
  • + – A plus sign indicates an element that can be included one or more times.
  • | – A bar indicates options.
Symbol   Expression
SelectStatement = select Parameters
Parameters = { FindOption } [ FieldList from ] TableBufferVariable [ IndexClause ] [ Options ] [ WhereClause ] [ JoinClause ]
FindOption = crossCompany [: ContainerVariable] | reverse | firstFast | FirstOption | forUpdate | noFetch | ForceOption | forceSelectOrder | forceNestedLoop | LockOption | repeatableRead | validTimeState
FirstOption = firstOnly | firstOnly10 | firstOnly100 | firstOnly1000
LockOption = optimisticLock | pessimisticLock
ForceOption = forcePlaceholders | forceLiterals
FieldList = { Field } | *
Field = Aggregate ( FieldIdentifier ) | FieldIdentifier
Aggregate = sum | avg | minof | maxof | count
Options = OrderClause | IndexClause
OrderClause = [OrderBy [GroupBy]] | [GroupBy [OrderBy]]
OrderBy = order [by] FieldOrder {, FieldOrder }
GroupBy = group [by] FieldOrder {, FieldOrder }
FieldOrder = FieldIdentifier [ asc | desc ]
IndexClause = index IndexName | index hint IndexName
WhereClause = where Expression InClause
InClause = in List
JoinClause = [exists | notexists | outer ] join Parameters
ContainerVariable = A container.
Expression = An expression.
TableBufferVariable = The variable name for the results.
FieldIdentifier = The name of a field in the table.
IndexName = The name of an index for a table.
List = An array of values.

Aggregate functions

The aggregate functions perform calculations on a single field over a group of records.

  • The result is returned in the field that you perform the aggregate function over.
  • The fields in the results are the aggregate values and the fields in the group by clause.
  • You can count, average, or sum only integer and real fields.
  • In cases where the sum function will return null, no rows are returned.

Differences between X++ and SQL

In industry-standard SQL, a database query can contain aggregate functions. Examples include count(RecID) and sum(columnA). When an aggregate function is used, but no rows match the where clause, a row must be returned to hold the result of the aggregates. The row that is returned shows the value 0 (zero) for the count function and null for the sum function. X++ doesn't support the concept of null values for the database. Therefore, in cases where the sum function will return null, no row is returned to the user. Additionally, every data type has a specific value that is treated as a null value in some circumstances.

Grouping and ordering the query results

A query can have multiple group by clauses, but the fields can be qualified by a table name in only one group by clause. We recommend that you use table name qualifiers. The order by clause follows the same syntax patterns as group by. Both clauses, if they are provided, must appear after the join (or from) clause, and both must appear before any where clause that exists on the same join clause. We recommend that all group by, order by, and where clauses appear immediately after the last join clause. The following example shows a group by clause where a field is qualified by a table name.

CustTable custTable;
CustGroup custGroup;
struct groupSummary = new struct("int CustomerCount; str CustGroup");

while select count(CreditMax) from custTable
    join custGroup
    order by custGroup.Name
    group by custGroup.CustGroup
    where custTable.CustGroup == custGroup.CustGroup
        && custGroup.Name like "*Days*"
{

    groupSummary.value("CustomerCount", custTable.CreditMax);
    groupSummary.value("CustGroup", custGroup.CustGroup);
    info(groupSummary.toString());
}

// Example output:
// (CustomerCount:1; CustGroup:"1")
// (CustomerCount:3; CustGroup:"2")

Join tables

The following example shows how an inner join can be performed as part of a select statement. The example also shows an order by clause where each field is qualified by a table name. Therefore, you can use just one order by clause to control how the retrieved records are sorted.

CustTable custTable;
CustGroup custGroup;
struct output = new struct("int AccountNum; str CustGroup");

while select AccountNum from custTable
    join Name from custGroup
    order by custGroup.Name, custTable.AccountNum
    where custTable.CustGroup == custGroup.CustGroup
{
    info(custGroup.Name + ': ' + custTable.AccountNum);
}

// Example output:
// Days1: 6000
// Days1: 6001
// Days2: 5000

Using where, order by, and index hint together in a query

You use the order by keyword in select statements to order the data that is returned. Use the index hint keyword to specify the index that should be used in the query, and to sort the selected records in the manner that is defined by the index. Indexes optimize the selection of records. To select records in a specific order, combine the index hint keyword with an order by expression. If you want the output to be sorted in reverse order, use the reverse keyword. If a table index has been disabled (that is, if the index's Enabled property is set to No), the select statement that references the index is still valid. However, the database can't use the index as a hint to sort the data, because the index doesn't exist in the database. The following table shows how to use the index hint and order by keywords in select statements.

Task select statement
Select records when the order isn't significant. select .. where ...
Select records when the order is significant. select .. order by ... where ...
Select records, and force a specific index to be used. select .. index hint ... where ...
Select records when the order is significant, and force a specific index to be used. select .. index hint ... order by ... where ...

The following example shows how to select transactions from the SalesTable table, based on a range of customers and due dates.

SalesTable salesTable;
select salesTable
    index hint CustIdx
    order by CustAccount
    where
        salesTable.CustAccount >= '3000'
        && salesTable.CustAccount <= '4000'
        && salesTable.FixedDueDate >= 12\12\2004
        && salesTable.FixedDueDate <= 05\05\2009;

asc keyword

The asc keyword is an option on the order by or group by clause. It specifies an ascending sort order. If neither asc nor desc is specified, the sort is ascending.

CustTable custTable;
select * from custTable
    order by Value asc;

avg keyword

The avg keyword returns the average of the fields.

CustTable custTable;
select avg(Value) from custTable;
info(int642Str(custTable.Value));

count keyword

The count keyword returns the number of records.

CustTable custTable;
int64 iCountRows;
select count(RecID) from custTable;
iCountRows = custTable.RecID;
info('Rows: ' + int642Str(iCountRows));

crossCompany keyword

The crossCompany keyword returns data for all companies that the user is authorized to read from. You can add a container to reduce the number of companies that are involved. The following example returns data for companies that the user is authorized to read from. Results are limited to the dat and dmo companies.

CustTable custTable;
container conCompanies = ['dat','dmo'];
select crossCompany :conCompanies
    * from custTable;

crossCompany clause can contain arbitrary expressions

The crossCompany clause can be used on select statements to indicate the companies that the search statement should take into account. The syntax has been enhanced to allow arbitrary expressions (of type container) instead of a single identifier, which is a variable of type container.

This code examples creates a container with the companies.

private void SampleMethod()
{
    MyTable t;
    container mycompanies = ['dat', 'dmo'];
    select crosscompany: mycompanies t;
}

This code uses an expression instead of the variable.

private void SampleMethod()
{
    MyTable t;
    container mycompanies = ['dat', 'dmo'];
    select crosscompany: (['dat'] + ['dmo']) t;
}

desc keyword

The desc keyword is an option on the order by or group by clause. It specifies a descending sort order. If neither asc nor desc is specified, the sort is ascending.

CustTable custTable;
select * from custTable
    order by Value desc;

exists keyword

The exists keyword is a method that returns a Boolean value and a join clause.

CtrTable ctrTable;
CustTable custTable;
while select AccountNum, Value from custTable
    order by AccountNum
    exists join * from ctrTable
    where (ctrTable.AccountNum == custTable.AccountNum)
{
}

firstFast keyword

The firstFast keyword is 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 pages.

The following code example quickly returns the first row.

CustTable custTable;
select firstFast custTable
    order by AccountNum;

firstOnly, firstOnly10, firstOnly100, and firstOnly1000 keywords

The firstOnly keywords speed up the fetch by returning a limited number of rows. When you include firstOnly in your query, the runtime returns a table buffer. When you omit firstOnly, the runtime allocates an object that can iterate over records. From a performance perspective, you should use firstOnly only when your intent is to fetch the first record.

Keyword Description
firstOnly Return only the first row.
firstOnly10 Return 10 rows.
firstOnly100 Return 100 rows.
firstOnly1000 Return 1,000 rows.

The following code example returns only the first row of the results.

CustTable custTable;
select firstOnly custTable
    index hint AccountIdx
    where custTable.AccountNum == '5000';

forceLiterals keyword

The forceLiterals keyword 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. The forceLiterals and forcePlaceholders keywords are mutually exclusive. For more information, see the forcePlaceholders keyword section.

Warning

You should not use the forceLiterals keyword in select statements, because it could expose code to an SQL injection security threat.

forceNestedLoop keyword

The forceNestedLoop keyword forces the SQL Server database to use a nested-loop algorithm to process a particular SQL statement that contains a join algorithm. Therefore, a record from the first table is fetched before any records from the second table are fetched. Typically, other join algorithms, such as hash joins and merge joins, are considered. This keyword is often combined with the forceSelectOrder keyword.

CustGroup custGroup;
CustTable custTable;

while select forceNestedLoop custGroup
    join custTable
    where custGroup.CustGroup == custTable.CustGroup
{
    Info(custTable.CustGroup);
}

forcePlaceholders keyword

The forcePlaceholders keyword instructs the kernel not to reveal the actual values that are used in where clauses to the SQL Server database at the time of optimization. By default, this behavior is used in all statements that aren't join statements. The advantage of using this keyword is that the kernel can reuse the access plan for similar statements that have other search values. The disadvantage is that, although the access plan is computed, the fact that data distribution might be uneven isn't considered. The access plan is an on-average access plan. The forcePlaceholders and forceLiterals keywords are mutually exclusive.

The following example iterates through the CustGroup table that is joined with the CustTable table.

CustGroup custGroup;
CustTable custTable;

while select forcePlaceholders custGroup
    join custTable
    where custGroup.CustGroup == custTable.CustGroup
{
    Info(custTable.CustGroup);
}

forceSelectOrder keyword

The forceSelectOrder keyword forces the SQL Server database to access the tables in a join in 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.

The following example joins the CustGroup and CustTable tables on the CustGroup field.

CustGroup custGroup;
CustTable custTable;

while select forceSelectOrder custGroup
    join custTable
    where custGroup.CustGroup == custTable.CustGroup
{
    Info(custTable.CustGroup);
}

forUpdate keyword

The forUpdate keyword selects records for update only. Depending on the underlying database, the records might be locked for other users. The following example selects the CreditMax column in the CustTable table for update, for the record where the AccountNum value is 2000.

ttsBegin;
    CustTable custTable;
    select forUpdate custTable
        where custTable.AccountNum == '2000';
    custTable.CreditMax = 5000;
    custTable.update();
ttsCommit;

group by keyword

The group by keyword instructs the database to group selected records by fields.

CustTable custTable;
while select sum(CreditMax) from custTable
    group by CustGroup
{
    info(custTable.CustGroup + ' ' + int642Str(custTable.CreditMax));
}

in keyword

The in keyword filters rows where a value is contained in a list.

If you don't use the in keyword, the code that you write will resemble the following example.

// This code doesn't use the in keyword.
private CostAmountStdAdjustment calcCostAmountStdAdjustment()
{
    InventSettlement inventSettlement;

    select sum(CostAmountAdjustment) from inventSettlement
        where inventSettlement.TransRecId == this.RecId
            && inventSettlement.Cancelled == NoYes::No
            && (inventSettlement.OperationsPosting == LedgerpostingType::purchStdProfit
                || inventSettlement.OperationsPosting == LedgerpostingType::purchStdLoss
                || inventSettlement.OperationsPosting == LedgerpostingType::InventStdProfit
                || inventSettlement.OperationsPosting == LedgerpostingType::InventStdLoss);

    return inventSettlement.CostAmountAdjustment;
}

If you use the in keyword, the code that you write will resemble the following example.

// This code uses the in keyword.
private CostAmountStdAdjustment calcCostAmountStdAdjustment()
{
    InventSettlement inventSettlement;
    container ledgerPostingTypes = this.ledgerPostingTypesForCostAmountStdAdjustmentCalculation();

    select sum(CostAmountAdjustment) from inventSettlement
        where inventSettlement.TransRecId == this.RecId
            && inventSettlement.Cancelled == NoYes::No
            && inventSettlement.OperationsPosting in ledgerPostingTypes;

    return inventSettlement.CostAmountAdjustment;
}

protected container ledgerPostingTypesForCostAmountStdAdjustmentCalculation()
{
return [
    LedgerPostingType::purchStdProfit,
    LedgerPostingType::PurchStdLoss,
    LedgerPostingType::InventStdProfit,
    LedgerPostingType::InventStdLoss
];
}

index keyword

The index keyword instructs the database to sort the selected records as specified by the index.

CustTable custTable;
while select AccountNum, Value from custTable
    index AccountIdx
{
    Info(custTable.AccountNum +  ": " + int642Str(custTable.Value));
}

index hint keyword

The index hint keyword forces SQL Server to use a specific index. Using index hint keyword, means you take away the control of which index to use from the Query Optimizer. An incorrect index hint can greatly affect performance. Index hints should be applied only to SQL statements that don't have dynamic where clauses or order by clauses, and where the effect of the hint can be verified.

Before you can use index hint in queries, you must call allowIndexHint(true) on the table. The default behavior for index hint is false, and the hint is ignored.

Warning

You should use index hint sparingly and with caution, and only when you can be sure that it improves performance. The index hint keyword and API let you pass the correct hints when they are required. If you're ever in doubt, avoid using index hint.

In the following example, the AccountIdx index is used to sort the records in the query on the CustTable table.

str _accountNum = '111';
CustTable custTable;
custTable.allowIndexHint(true);

while select forUpdate custTable
    index hint AccountIdx
    where custTable.AccountNum == _accountNum
{
}

join keyword

The join keyword is used to join tables on a column that is shared by both tables. The join criteria are specified in a where clause, because there is no on keyword, such as is found in SQL. This keyword reduces the number of SQL statements that are required if you want to loop through a table and update transactions in a related table. For example, you process 500 records in a table and want to update related records in another table. If you use a nested while select, there will be 501 trips to the database. However, if you use a join, there will be just one trip to the database.

CustTable custTable;
CustGroup custGroup;
int totalCredit;

while select custGroup
    join custTable
    where custGroup.CustGroup == custTable.CustGroup
{
    totalCredit += custTable.CreditMax;
}
}

maxof keyword

The maxof keyword returns the maximum of the fields.

CustTable custTable;
select maxof(CreditMax) from custTable;
info(int642Str(custTable.Value));

minof keyword

The minof keyword returns the minimum of the fields.

CustTable custTable;
select minof(CreditMax) from custTable;
info(int642Str(custTable.Value));

noFetch keyword

The noFetch keyword indicates that no records should be fetched now. Typically, this keyword is used when the result of the select statement is passed on to another application object, such as a query that performs the actual fetch.

The following example creates a query variable but doesn't fetch the records.

CustTable custTable;
select noFetch custTable
    order by AccountNum;

notExists keyword

The notExists keyword is selected only if there are no posts.

CustTable custTable;
CtrTable ctrTable;

while select AccountNum, Value from custTable
    order by AccountNum
    notExists join * from ctrTable
    where (ctrTable.AccountNum == custTable.AccountNum)
{
}

optimisticLock keyword

The optimisticLock keyword forces a statement to run by using optimistic concurrency control, even if a different value is set on the table.

CustTable custTable;
select optimisticLock custTable
    where custTable.AccountNum > '1000';

order by keyword

The order by keyword instructs the database to sort the selected records by the fields in the order by list. The keyword by is optional.

CustTable custTable;
select * from custTable
    order by accountNum desc
    where custTable.AccountNum > '100';
info("AccountNum: " + custTable.AccountNum);

The following example prints the highest AccountNum value in the CustTable table.

CustTable custTable;
select reverse custTable
    order by accountNum;
info("AccountNum: " + custTable.AccountNum);

outer keyword

The outer keyword returns all rows from the table that is named first, even rows that have no match in the table that is named second. This join is a left outer join. Default values are substituted for any data that could not be obtained from a matching row in the other joined table.

There is no left keyword, and there is no right outer join.

For an inner join, the behavior if you filter on an on clause is the same as the behavior if you filter on the where clause.

CustTable custTable;
CustGroup custGroupTable;

while select CustGroup from custGroupTable
    order by CustGroup
    outer join * from custGroupTable
    where custTable.CustGroup == custGroupTable.CustGroup
{
    Info(custTable.CustGroup + ', ' + custGroupTable.Name);
}

The following example is based on two tables. The field types and example data are included. There is a one-to-many relationship between the SalesOrder parent table and the SalesOrderLine child table. For each row in the SalesOrder table, there are 0 (zero) or more rows in the SalesOrderLine table. There are two rows in the SalesOrder table.

SalesOrderID (integer, primary key) DateAdded (date)
1 2010-01-01
2 2010-02-02

The SalesOrderLine table contains a foreign key field that is named SalesOrderID. This field references the primary key column of the SalesOrder table. A SalesOrderID value of 2 doesn't occur in the data for the SalesOrderLine table.

SalesOrderLineID (string, primary key) Quantity (integer) SalesOrderID (integer, foreign key)
AA 32 1
BB 67 1
CC 66 1

The following code has a select statement that reads the two tables. The select statement includes a left outer join clause. Both the join criteria and the data filter are on the where clause. The output from the code is also shown. The second record in the output has a SalesOrderID value of 2. However, that value isn't present in the SalesOrderLine table. Therefore, some of the fields in the second record have default values: 0 for an integer and a zero-length string for a string.

SalesOrder recSalesOrder;
SalesOrderLine recSalesOrderLine;
struct struct4 = new struct
    ("int SalesOrderID;"
    + "date DateAdded;"
    + "str SalesOrderLineID;"
    + "int Quantity"
    );
while select *
    from
        recSalesOrder
        outer join recSalesOrderLine
    where
        recSalesOrder.SalesOrderID == recSalesOrderLine.SalesOrderID
        && recSalesOrderLine.Quantity == 66
{
    struct4.value("SalesOrderID", recSalesOrder.SalesOrderID);
    struct4.value("DateAdded", recSalesOrder.DateAdded);
    struct4.value("SalesOrderLineID", recSalesOrderLine.SalesOrderLineID);
    struct4.value("Quantity", recSalesOrderLine.Quantity);
    info(struct4.toString());
}

// Example output:
// (SalesOrderID:1; DateAdded:2010/1/1; SalesOrderLineID:"CC"; Quantity:66)
// (SalesOrderID:2; DateAdded:2010/2/2; SalesOrderLineID:""; Quantity:0)

pessimisticLock keyword

The pessimisticLock keyword forces a statement to run by using pessimistic concurrency control, even if a different value is set on the table.

CustTable custTable;
select pessimisticLock custTable
    where custTable.AccountNum > '1000';

repeatableRead keyword

This repeatableRead keyword specifies that the current transaction must be completed before other transactions can modify data that has been read by logic inside the current transaction. An explicit transaction is completed at either ttsAbort or the outermost ttsCommit. For a standalone 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 if this keyword doesn't appear in your code. (The behavior depends on the method that the database uses to determine whether it should scan the tables.) For more information, see the documentation for the underlying relational database product.

reverse keyword

The reverse keyword returns records in reverse order.

CustTable custTable;
select reverse custTable
    order by AccountNum;

sum keyword

The sum keyword returns the sum of the fields. It can be used to sum all accounts, order lines, and so on.

CustTable custTable;
select sum(CreditMax) from custTable;
info(int642Str(custTable.Value));

validTimeState keyword

The validTimeState keyword selects rows from a table where the ValidTimeStateFieldType property is set to a value other than None.

CustPackingSlipTransHistory history;
utcDateTime dateFrom, dateTo = DateTimeUtil::utcNow();
anytype recid = -1;
select
    validTimeState(dateFrom, dateTo)
    *
    from history;
recid = history.RecId;
info('RecId:' + int642Str(recid));

where keyword

The where keyword filters rows from a table where the expression is true.

The following example finds a customer that has an AccountNum value that is more than 100.

CustTable custTable;
select * from custTable
    where custTable.AccountNum > '100';
info("AccountNum: " + custTable.AccountNum);

The following examples prints the lowest AccountNum value that is more than 100.

CustTable custTable;
select * from custTable
    order by accountNum
    where custTable.AccountNum > '100';
info("AccountNum: " + custTable.AccountNum);

The following example prints the highest AccountNum value that is more than 100.

CustTable custTable;
select * from custTable
    order by accountNum desc
    where custTable.accountNum > "100";
info("AccountNum: " + custTable.AccountNum);