Aggregate (H2 Database Engine wt-1.0.1 API)

java.lang.Object
- org.h2.expression.Expression
- - org.h2.expression.Aggregate

```
public class Aggregate
extends Expression
```
Implements the integrated aggregate functions, such as COUNT, MAX, SUM.

字段概要

字段
限定符和类型	字段和说明
`static int`	`COUNT` The aggregate type for COUNT(expression).
`static int`	`COUNT_ALL` The aggregate type for COUNT(*).
`static int`	`GROUP_CONCAT` The aggregate type for GROUP_CONCAT(...).

构造器概要

构造器
构造器和说明

Aggregate(int type, Expression on, Select select, boolean distinct)
Create a new aggregate object.

构造器
构造器和说明
`Aggregate(int type, Expression on, Select select, boolean distinct)` Create a new aggregate object.

方法概要

所有方法静态方法实例方法具体方法
限定符和类型	方法和说明
`static int`	`getAggregateType(String name)` Get the aggregate type for this name, or -1 if no aggregate has been found.
`int`	`getCost()` Estimate the cost to process the expression.
`int`	`getDisplaySize()` Get the display size of this expression.
`long`	`getPrecision()` Get the precision of this expression.
`int`	`getScale()` Get the scale of this expression.
`String`	`getSQL()` Get the SQL statement of this expression.
`int`	`getType()` Return the data type.
`Value`	`getValue(Session session)` Return the resulting value for the current row.
`boolean`	`isEverything(ExpressionVisitor visitor)` Check if this expression and all sub-expressions can fulfill a criteria.
`void`	`mapColumns(ColumnResolver resolver, int level)` Map the columns of the resolver to expression columns.
`Expression`	`optimize(Session session)` Try to optimize the expression.
`void`	`setEvaluatable(TableFilter tableFilter, boolean b)` Tell the expression columns whether the table filter can return values now.
`void`	`setGroupConcatOrder(ArrayList<SelectOrderBy> orderBy)` Set the order for GROUP_CONCAT() aggregate.
`void`	`setGroupConcatSeparator(Expression separator)` Set the separator for the GROUP_CONCAT() aggregate.
`void`	`updateAggregate(Session session)` Update an aggregate value.

从类继承的方法 org.h2.expression.Expression
addFilterConditions, createIndexConditions, getAlias, getBooleanValue, getColumnName, getExpressionColumns, getExpressionColumns, getNonAliasExpression, getNotIfPossible, getNullable, getSchemaName, getTableAlias, getTableName, isAutoIncrement, isConstant, isValueSet, isWildcard, toString

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- 字段详细资料
  - COUNT_ALL
```
public static final int COUNT_ALL
```
    The aggregate type for COUNT(*).
    
    另请参阅:
    
    常量字段值
  - COUNT
```
public static final int COUNT
```
    The aggregate type for COUNT(expression).
    
    另请参阅:
    
    常量字段值
  - GROUP_CONCAT
```
public static final int GROUP_CONCAT
```
    The aggregate type for GROUP_CONCAT(...).
    
    另请参阅:
    
    常量字段值
- 构造器详细资料
  - Aggregate
```
public Aggregate(int type,
                 Expression on,
                 Select select,
                 boolean distinct)
```
    Create a new aggregate object.
    
    参数:
    
    type - the aggregate type
    
    on - the aggregated expression
    
    select - the select statement
    
    distinct - if distinct is used
- 方法详细资料
  - getAggregateType
```
public static int getAggregateType(String name)
```
    Get the aggregate type for this name, or -1 if no aggregate has been found.
    
    参数:
    
    name - the aggregate function name
    
    返回:
    
    -1 if no aggregate function has been found, or the aggregate type
  - setGroupConcatOrder
```
public void setGroupConcatOrder(ArrayList<SelectOrderBy> orderBy)
```
    Set the order for GROUP_CONCAT() aggregate.
    
    参数:
    
    orderBy - the order by list
  - setGroupConcatSeparator
```
public void setGroupConcatSeparator(Expression separator)
```
    Set the separator for the GROUP_CONCAT() aggregate.
    
    参数:
    
    separator - the separator expression
  - updateAggregate
```
public void updateAggregate(Session session)
```
    从类复制的说明: Expression
    
    Update an aggregate value. This method is called at statement execution time. It is usually called once for each row, but if the expression is used multiple times (for example in the column list, and as part of the HAVING expression) it is called multiple times - the row counter needs to be used to make sure the internal state is only updated once.
    
    指定者:
    
    updateAggregate 在类中 Expression
    
    参数:
    
    session - the session
  - getValue
```
public Value getValue(Session session)
```
    从类复制的说明: Expression
    
    Return the resulting value for the current row.
    
    指定者:
    
    getValue 在类中 Expression
    
    参数:
    
    session - the session
    
    返回:
    
    the result
  - getType
```
public int getType()
```
    从类复制的说明: Expression
    
    Return the data type. The data type may not be known before the optimization phase.
    
    指定者:
    
    getType 在类中 Expression
    
    返回:
    
    the type
  - mapColumns
```
public void mapColumns(ColumnResolver resolver,
                       int level)
```
    从类复制的说明: Expression
    
    Map the columns of the resolver to expression columns.
    
    指定者:
    
    mapColumns 在类中 Expression
    
    参数:
    
    resolver - the column resolver
    
    level - the subquery nesting level
  - optimize
```
public Expression optimize(Session session)
```
    从类复制的说明: Expression
    
    Try to optimize the expression.
    
    指定者:
    
    optimize 在类中 Expression
    
    参数:
    
    session - the session
    
    返回:
    
    the optimized expression
  - setEvaluatable
```
public void setEvaluatable(TableFilter tableFilter,
                           boolean b)
```
    从类复制的说明: Expression
    
    Tell the expression columns whether the table filter can return values now. This is used when optimizing the query.
    
    指定者:
    
    setEvaluatable 在类中 Expression
    
    参数:
    
    tableFilter - the table filter
    
    b - true if the table filter can return value
  - getScale
```
public int getScale()
```
    从类复制的说明: Expression
    
    Get the scale of this expression.
    
    指定者:
    
    getScale 在类中 Expression
    
    返回:
    
    the scale
  - getPrecision
```
public long getPrecision()
```
    从类复制的说明: Expression
    
    Get the precision of this expression.
    
    指定者:
    
    getPrecision 在类中 Expression
    
    返回:
    
    the precision
  - getDisplaySize
```
public int getDisplaySize()
```
    从类复制的说明: Expression
    
    Get the display size of this expression.
    
    指定者:
    
    getDisplaySize 在类中 Expression
    
    返回:
    
    the display size
  - getSQL
```
public String getSQL()
```
    从类复制的说明: Expression
    
    Get the SQL statement of this expression. This may not always be the original SQL statement, specially after optimization.
    
    指定者:
    
    getSQL 在类中 Expression
    
    返回:
    
    the SQL statement
  - isEverything
```
public boolean isEverything(ExpressionVisitor visitor)
```
    从类复制的说明: Expression
    
    Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.
    
    指定者:
    
    isEverything 在类中 Expression
    
    参数:
    
    visitor - the visitor
    
    返回:
    
    if the criteria can be fulfilled
  - getCost
```
public int getCost()
```
    从类复制的说明: Expression
    
    Estimate the cost to process the expression. Used when optimizing the query, to calculate the query plan with the lowest estimated cost.
    
    指定者:
    
    getCost 在类中 Expression
    
    返回:
    
    the estimated cost

类 Aggregate

字段概要

构造器概要

方法概要

从类继承的方法 org.h2.expression.Expression

从类继承的方法 java.lang.Object

字段详细资料

COUNT_ALL

COUNT

GROUP_CONCAT

构造器详细资料

Aggregate

方法详细资料

getAggregateType

setGroupConcatOrder

setGroupConcatSeparator

updateAggregate

getValue

getType

mapColumns

optimize

setEvaluatable

getScale

getPrecision

getDisplaySize

getSQL

isEverything

getCost