org.apache.metamodel.query

Class SelectItem

java.lang.Object

org.apache.metamodel.util.BaseObject

org.apache.metamodel.query.SelectItem

All Implemented Interfaces:

Serializable, Cloneable, QueryItem

public class SelectItem
extends BaseObject
implements QueryItem, Cloneable

Represents a SELECT item. SelectItems can take different forms:

• column SELECTs (selects a column from a table)
• column function SELECTs (aggregates the values of a column)
• expression SELECTs (retrieves data based on an expression (only supported for JDBC datastores)
• expression function SELECTs (retrieves databased on a function and an expression, only COUNT(*) is supported for non-JDBC datastores))
• SELECTs from subqueries (works just like column selects, but in stead of pointing to a column, it retrieves data from the select item of a subquery)

See Also:

SelectClause, Serialized Form

Constructor Summary

Constructors

Constructor and Description
SelectItem(Column column) Creates a simple SelectItem that selects from a column
SelectItem(Column column, FromItem fromItem) Creates a SelectItem that references a column from a particular FromItem, for example a.price or p.age
SelectItem(FunctionType function, Column column) Creates a SelectItem that uses a function on a column, for example SUM(price) or MAX(age)
SelectItem(FunctionType function, Column column, FromItem fromItem) Creates a SelectItem that uses a function on a column from a particular FromItem, for example SUM(a.price) or MAX(p.age)
SelectItem(FunctionType function, String expression, String alias) Creates a SelectItem based on a function and an expression.
SelectItem(SelectItem subQuerySelectItem, FromItem subQueryFromItem) Creates a SelectItem that references another select item in a subquery
SelectItem(String expression, String alias) Creates a SelectItem based on an expression.

Method Summary

Methods

Modifier and Type	Method and Description
protected SelectItem	clone()
protected void	decorateIdentity(List<Object> identifiers) Subclasses should implement this method and add all fields to the list that are to be included in equals(...) and hashCode() evaluation
boolean	equalsIgnoreAlias(SelectItem that)
boolean	equalsIgnoreAlias(SelectItem that, boolean exactColumnCompare)
String	getAlias()
Column	getColumn()
static SelectItem	getCountAllItem() Generates a COUNT(*) select item
ColumnType	getExpectedColumnType() Tries to infer the ColumnType of this SelectItem.
String	getExpression()
FromItem	getFromItem()
FunctionType	getFunction()
Query	getQuery()
String	getSameQueryAlias()
String	getSameQueryAlias(boolean includeSchemaInColumnPath)
FromItem	getSubQueryFromItem() Deprecated. use getFromItem() instead
SelectItem	getSubQuerySelectItem()
String	getSuperQueryAlias()
String	getSuperQueryAlias(boolean includeQuotes)
static boolean	isCountAllItem(SelectItem item)
boolean	isFunctionApproximationAllowed()
boolean	isReferenced(Column column) Investigates whether or not this SelectItem references a particular column.
SelectItem	replaceFunction(FunctionType function) Creates a copy of the SelectItem, with a different FunctionType.
SelectItem	setAlias(String alias)
void	setFunctionApproximationAllowed(boolean functionApproximationAllowed)
SelectItem	setQuery(Query query)
String	toSql()
String	toSql(boolean includeSchemaInColumnPath)
String	toString()
StringBuilder	toStringNoAlias()
StringBuilder	toStringNoAlias(boolean includeSchemaInColumnPath)

Methods inherited from class org.apache.metamodel.util.BaseObject

classEquals, equals, hashCode

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

SelectItem

public SelectItem(Column column)

Creates a simple SelectItem that selects from a column

Parameters:

column -

SelectItem

public SelectItem(FunctionType function,
          Column column)

Creates a SelectItem that uses a function on a column, for example SUM(price) or MAX(age)

Parameters:

function -

column -

SelectItem

public SelectItem(Column column,
          FromItem fromItem)

Creates a SelectItem that references a column from a particular FromItem, for example a.price or p.age

Parameters:

column -

fromItem -

SelectItem

public SelectItem(FunctionType function,
          Column column,
          FromItem fromItem)

Creates a SelectItem that uses a function on a column from a particular FromItem, for example SUM(a.price) or MAX(p.age)

Parameters:

function -

column -

fromItem -

SelectItem

public SelectItem(String expression,
          String alias)

Creates a SelectItem based on an expression. All expression-based SelectItems must have aliases.

Parameters:

expression -

alias -

SelectItem

public SelectItem(FunctionType function,
          String expression,
          String alias)

Creates a SelectItem based on a function and an expression. All expression-based SelectItems must have aliases.

Parameters:

function -

expression -

alias -

SelectItem

public SelectItem(SelectItem subQuerySelectItem,
          FromItem subQueryFromItem)

Creates a SelectItem that references another select item in a subquery

Parameters:

subQuerySelectItem -

subQueryFromItem - the FromItem that holds the sub-query

Method Detail

getCountAllItem

public static SelectItem getCountAllItem()

Generates a COUNT(*) select item

isCountAllItem

public static boolean isCountAllItem(SelectItem item)

getAlias

public String getAlias()

setAlias

public SelectItem setAlias(String alias)

getFunction

public FunctionType getFunction()

isFunctionApproximationAllowed

public boolean isFunctionApproximationAllowed()

Returns:

if this is a function based SelectItem where function calculation is allowed to be approximated (if the datastore type has an approximate calculation method). Approximated function results are as the name implies not exact, but might be valuable as an optimization in some cases.

setFunctionApproximationAllowed

public void setFunctionApproximationAllowed(boolean functionApproximationAllowed)

getColumn

public Column getColumn()

getExpectedColumnType

public ColumnType getExpectedColumnType()

Tries to infer the ColumnType of this SelectItem. For expression based select items, this is not possible, and the method will return null.

Returns:

getExpression

public String getExpression()

setQuery

public SelectItem setQuery(Query query)

Specified by:

setQuery in interface QueryItem

getQuery

public Query getQuery()

Specified by:

getQuery in interface QueryItem

getSubQuerySelectItem

public SelectItem getSubQuerySelectItem()

getSubQueryFromItem

@Deprecated
public FromItem getSubQueryFromItem()

Deprecated. use getFromItem() instead

getFromItem

public FromItem getFromItem()

getSuperQueryAlias

public String getSuperQueryAlias()

Returns:

the name that this SelectItem can be referenced with, if referenced from a super-query. This will usually be the alias, but if there is no alias, then the column name will be used.

getSuperQueryAlias

public String getSuperQueryAlias(boolean includeQuotes)

Parameters:

includeQuotes - indicates whether or not the output should include quotes, if the select item's column has quotes associated (typically true, but false if used for presentation)

Returns:

the name that this SelectItem can be referenced with, if referenced from a super-query. This will usually be the alias, but if there is no alias, then the column name will be used.

getSameQueryAlias

public String getSameQueryAlias()

getSameQueryAlias

public String getSameQueryAlias(boolean includeSchemaInColumnPath)

Returns:

an alias that can be used in WHERE, GROUP BY and ORDER BY clauses in the same query

toSql

public String toSql()

Specified by:

toSql in interface QueryItem

toSql

public String toSql(boolean includeSchemaInColumnPath)

Specified by:

toSql in interface QueryItem

toStringNoAlias

public StringBuilder toStringNoAlias()

toStringNoAlias

public StringBuilder toStringNoAlias(boolean includeSchemaInColumnPath)

equalsIgnoreAlias

public boolean equalsIgnoreAlias(SelectItem that)

equalsIgnoreAlias

public boolean equalsIgnoreAlias(SelectItem that,
                        boolean exactColumnCompare)

decorateIdentity

protected void decorateIdentity(List<Object> identifiers)

Description copied from class: BaseObject

Subclasses should implement this method and add all fields to the list that are to be included in equals(...) and hashCode() evaluation

Specified by:

decorateIdentity in class BaseObject

clone

protected SelectItem clone()

Overrides:

clone in class Object

replaceFunction

public SelectItem replaceFunction(FunctionType function)

Creates a copy of the SelectItem, with a different FunctionType.

Parameters:

function -

Returns:

isReferenced

public boolean isReferenced(Column column)

Investigates whether or not this SelectItem references a particular column. This will search for direct references and indirect references via subqueries.

Parameters:

column -

Returns:

a boolean that is true if the specified column is referenced by this SelectItem and false otherwise.

toString

public String toString()

Specified by:

toString in interface QueryItem

Overrides:

toString in class BaseObject