ExpressionColumn (H2 Database Engine wt-1.0.1 API)

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

```
public class ExpressionColumn
extends Expression
```
A expression that represents a column of a table or view.

构造器概要

构造器
构造器和说明
`ExpressionColumn(Database database, Column column)`
`ExpressionColumn(Database database, String schemaName, String tableAlias, String columnName)`

方法概要

所有方法实例方法具体方法
限定符和类型	方法和说明
`void`	`createIndexConditions(Session session, TableFilter filter)` Create index conditions if possible and attach them to the table filter.
`String`	`getAlias()` Get the alias name of a column or SQL expression if it is not an aliased expression.
`Column`	`getColumn()`
`String`	`getColumnName()` Get the column name or alias name of this expression.
`int`	`getCost()` Estimate the cost to process the expression.
`int`	`getDisplaySize()` Get the display size of this expression.
`Expression`	`getNotIfPossible(Session session)` If it is possible, return the negated expression.
`int`	`getNullable()` Check whether this expression is a column and can store NULL.
`String`	`getOriginalColumnName()`
`String`	`getOriginalTableAliasName()`
`long`	`getPrecision()` Get the precision of this expression.
`int`	`getScale()` Get the scale of this expression.
`String`	`getSchemaName()` Get the schema name, or null
`String`	`getSQL()` Get the SQL statement of this expression.
`TableFilter`	`getTableFilter()`
`String`	`getTableName()` Get the table name, or null
`int`	`getType()` Return the data type.
`Value`	`getValue(Session session)` Return the resulting value for the current row.
`boolean`	`isAutoIncrement()` Check if this is an auto-increment column.
`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`	`updateAggregate(Session session)` Update an aggregate value.

从类继承的方法 org.h2.expression.Expression
addFilterConditions, getBooleanValue, getExpressionColumns, getExpressionColumns, getNonAliasExpression, getTableAlias, isConstant, isValueSet, isWildcard, toString

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

- 构造器详细资料
  - ExpressionColumn
```
public ExpressionColumn(Database database,
                        Column column)
```
  - ExpressionColumn
```
public ExpressionColumn(Database database,
                        String schemaName,
                        String tableAlias,
                        String columnName)
```
- 方法详细资料
  - 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
  - getTableFilter
```
public TableFilter getTableFilter()
```
  - 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
  - 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
  - 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
  - getColumn
```
public Column getColumn()
```
  - 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
  - getOriginalColumnName
```
public String getOriginalColumnName()
```
  - getOriginalTableAliasName
```
public String getOriginalTableAliasName()
```
  - getColumnName
```
public String getColumnName()
```
    从类复制的说明: Expression
    
    Get the column name or alias name of this expression.
    
    覆盖:
    
    getColumnName 在类中 Expression
    
    返回:
    
    the column name
  - getSchemaName
```
public String getSchemaName()
```
    从类复制的说明: Expression
    
    Get the schema name, or null
    
    覆盖:
    
    getSchemaName 在类中 Expression
    
    返回:
    
    the schema name
  - getTableName
```
public String getTableName()
```
    从类复制的说明: Expression
    
    Get the table name, or null
    
    覆盖:
    
    getTableName 在类中 Expression
    
    返回:
    
    the table name
  - getAlias
```
public String getAlias()
```
    从类复制的说明: Expression
    
    Get the alias name of a column or SQL expression if it is not an aliased expression.
    
    覆盖:
    
    getAlias 在类中 Expression
    
    返回:
    
    the alias name
  - isAutoIncrement
```
public boolean isAutoIncrement()
```
    从类复制的说明: Expression
    
    Check if this is an auto-increment column.
    
    覆盖:
    
    isAutoIncrement 在类中 Expression
    
    返回:
    
    true if it is an auto-increment column
  - getNullable
```
public int getNullable()
```
    从类复制的说明: Expression
    
    Check whether this expression is a column and can store NULL.
    
    覆盖:
    
    getNullable 在类中 Expression
    
    返回:
    
    whether NULL is allowed
  - 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
  - createIndexConditions
```
public void createIndexConditions(Session session,
                                  TableFilter filter)
```
    从类复制的说明: Expression
    
    Create index conditions if possible and attach them to the table filter.
    
    覆盖:
    
    createIndexConditions 在类中 Expression
    
    参数:
    
    session - the session
    
    filter - the table filter
  - getNotIfPossible
```
public Expression getNotIfPossible(Session session)
```
    从类复制的说明: Expression
    
    If it is possible, return the negated expression. This is used to optimize NOT expressions: NOT ID>10 can be converted to ID<=10. Returns null if negating is not possible.
    
    覆盖:
    
    getNotIfPossible 在类中 Expression
    
    参数:
    
    session - the session
    
    返回:
    
    the negated expression, or null

类 ExpressionColumn

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

构造器详细资料

ExpressionColumn

ExpressionColumn

方法详细资料

getSQL

getTableFilter

mapColumns

optimize

updateAggregate

getValue

getType

setEvaluatable

getColumn

getScale

getPrecision

getDisplaySize

getOriginalColumnName

getOriginalTableAliasName

getColumnName

getSchemaName

getTableName

getAlias

isAutoIncrement

getNullable

isEverything

getCost

createIndexConditions

getNotIfPossible