gudusoft.gsqlparser.nodes.teradata

Class TTeradataPeriodForClause

Object

gudusoft.gsqlparser.nodes.TParseTreeNode

gudusoft.gsqlparser.nodes.teradata.TTeradataPeriodForClause

All Implemented Interfaces:

Visitable, Iterator<TSourceToken>

public class TTeradataPeriodForClause
extends TParseTreeNode

Represents a Teradata PERIOD FOR clause that defines a derived temporal column.

Syntax:

 PERIOD FOR period_name (start_column, end_column) [AS VALIDTIME | AS TRANSACTIONTIME]
 

The PERIOD FOR clause creates a derived column that represents a time period spanning from start_column to end_column. This derived column can be used with temporal constraints like SEQUENCED VALIDTIME PRIMARY KEY.

Example:

 PERIOD FOR effective_period (eff_begin_dt, eff_end_dt) AS VALIDTIME
 

See Also:

Teradata PERIOD FOR Documentation

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TTeradataPeriodForClause.ETemporalType Temporal type for the PERIOD FOR clause.

Field Summary

Fields inherited from class gudusoft.gsqlparser.nodes.TParseTreeNode

dbvendor, doubleLinkedTokenListToString, nodeActionAppend, nodeActionInsert, nodeActionRemove, nodeActionUnknown, nodeActionUpdate, nodeActionUpdateText, nodeChangeEndToken, nodeChangeStartToken

Constructor Summary

Constructors

Constructor and Description
TTeradataPeriodForClause()

Method Summary

Modifier and Type	Method and Description
void	accept(TParseTreeVisitor v) Accept a visitor
void	acceptChildren(TParseTreeVisitor v) Accept a visitor to iterate this class and sub-nodes of this class
TObjectName	getEndColumnName() Gets the end column name for the period.
TObjectName	getPeriodName() Gets the name of the derived period column.
TObjectName	getStartColumnName() Gets the start column name for the period.
TTeradataPeriodForClause.ETemporalType	getTemporalType() Gets the temporal type (VALIDTIME, TRANSACTIONTIME, or none).
void	init(Object periodName, Object startColumnName, Object endColumnName) Initialize with period name and column references.
void	setEndColumnName(TObjectName endColumnName) Sets the end column name for the period.
void	setPeriodName(TObjectName periodName) Sets the name of the derived period column.
void	setStartColumnName(TObjectName startColumnName) Sets the start column name for the period.
void	setTemporalType(TTeradataPeriodForClause.ETemporalType temporalType) Sets the temporal type.
String	toString() 将一个语法树节点（TParseTreeNode）转换回它对应的原始SQL字符串。 它通过遍历一个由 startToken（起始词法单元）和 endToken（结束词法单元）界定的双向链表来实现这一功能。

Methods inherited from class gudusoft.gsqlparser.nodes.TParseTreeNode

addAllMyTokensToTokenList, addToTokenChain, appendNewNode, calculateTokenCount, doAppendNewNode, doParse, fastSetString, getAnchorNode, getColumnNo, getCommentAfterNode, getCommentBeforeNode, getCompactString, getDummyTag, getEndToken, getEvaluateDatatype, getEvalValue, getGsqlparser, getLineNo, getLocation, getMd5, getNodeStatus, getNodeType, getParentObjectName, getPlainText, getStartToken, getTokenCount, hasNext, init, init, init, init, init, init, init, init, init, insertAfterAToken, insertNewNodeBeforeMe, isChanged, isTokensInChain, next, refreshAllNodesTokenCount, remove, removeAllMyTokensFromTokenList, removeTokens, removeTokensBetweenNodes, removeTokensBetweenToken, replaceWithNewNode, resetIterator, setAnchorNode, setChanged, setDummyTag, setEndToken, setEndToken, setEndToken, setEndToken, setEndToken, setEndTokenDirectly, setEvaluateDatatype, setEvalValue, setGsqlparser, setIncludingComment, setLocation, setNewSubNode, setNodeStatus, setNodeType, setParent, setPlainText, setStartToken, setStartToken, setStartToken, setStartToken, setStartTokenDirectly, setString, setString2, subNodeInNode, toScript, toString2

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface Iterator

forEachRemaining

Constructor Detail

TTeradataPeriodForClause

public TTeradataPeriodForClause()

Method Detail

init

public void init(Object periodName,
                 Object startColumnName,
                 Object endColumnName)

Initialize with period name and column references.

Overrides:

init in class TParseTreeNode

Parameters:

periodName - the name of the derived period column

startColumnName - the start column of the period

endColumnName - the end column of the period

getPeriodName

public TObjectName getPeriodName()

Gets the name of the derived period column.

Returns:

the period column name

setPeriodName

public void setPeriodName(TObjectName periodName)

Sets the name of the derived period column.

Parameters:

periodName - the period column name

getStartColumnName

public TObjectName getStartColumnName()

Gets the start column name for the period.

Returns:

the start column reference

setStartColumnName

public void setStartColumnName(TObjectName startColumnName)

Sets the start column name for the period.

Parameters:

startColumnName - the start column reference

getEndColumnName

public TObjectName getEndColumnName()

Gets the end column name for the period.

Returns:

the end column reference

setEndColumnName

public void setEndColumnName(TObjectName endColumnName)

Sets the end column name for the period.

Parameters:

endColumnName - the end column reference

getTemporalType

public TTeradataPeriodForClause.ETemporalType getTemporalType()

Gets the temporal type (VALIDTIME, TRANSACTIONTIME, or none).

Returns:

the temporal type

setTemporalType

public void setTemporalType(TTeradataPeriodForClause.ETemporalType temporalType)

Sets the temporal type.

Parameters:

temporalType - the temporal type

accept

public void accept(TParseTreeVisitor v)

Description copied from class: TParseTreeNode

Accept a visitor

Specified by:

accept in interface Visitable

Overrides:

accept in class TParseTreeNode

Parameters:

v - visitor is a descendant class of TParseTreeVisitor

acceptChildren

public void acceptChildren(TParseTreeVisitor v)

Description copied from class: TParseTreeNode

Accept a visitor to iterate this class and sub-nodes of this class

Specified by:

acceptChildren in interface Visitable

Overrides:

acceptChildren in class TParseTreeNode

Parameters:

v - visitor is a descendant class of TParseTreeVisitor

toString

public String toString()

Description copied from class: TParseTreeNode

将一个语法树节点（TParseTreeNode）转换回它对应的原始SQL字符串。 它通过遍历一个由 startToken（起始词法单元）和 endToken（结束词法单元）界定的双向链表来实现这一功能。

这个方法的设计采用了“两遍扫描”（Two-Pass）的策略，也就是使用了两个 while 循环。 第一个循环是预处理阶段，用于清理格式；第二个循环则负责构建最终的字符串。

第一个 while 循环

这个循环的主要目标是识别并“软删除”多余的换行符（newline tokens）。这种情况尤其在SQL被程序动态修改后容易出现。 这个循环本身不构建字符串，只负责分析和更新词法单元的状态。 其工作原理是：

1. 遍历： 它从 startToken 开始，通过 getNextTokenInChain() 方法遍历到 endToken。
2. 检测链表变化： 它通过比较当前和前一个词法单元的 posinlist（词法单元在原始完整列表中的位置索引）来判断链表是否“自然”。 如果不连续，意味着词法单元被插入或重排了，此时 isChainModified 标志位会被设为 true。
3. 标记换行符： 当遇到第一个换行符时，它会设置一个标志。如果紧接着又遇到了另一个换行符，并且此时链表已经被修改过, 那么它会将这个多余的换行符标记为待删除状态。这个逻辑能有效地将代码被修改后可能产生的多个连续换行压缩成一个。

简而言之，第一个循环是一个格式清理过程，它为后续生成整洁的字符串做准备。

第二个 while 循环

这个循环负责从（经过第一步清理后的）词法单元流中实际地构建最终的输出字符串。 其工作原理是：

1. 遍历： 它再次遍历完全相同的词法单元序列。
2. 构建字符串： 在将每个词法单元追加到 StringBuffer 之前，它会进行检查。
3. 跳过特定单元： 如果一个词法单元在第一个循环中被标记为待删除，或者它是一个注释（且配置为不包含注释），那么它将被跳过。
4. 拼接字符串： 对于所有未被跳过的词法单元，它会将其字符串值追加到 StringBuffer 中。

当这个循环结束后，StringBuffer 就包含了该语法树节点的最终、重构后的SQL文本。

Overrides:

toString in class TParseTreeNode

Returns:

节点对应的SQL字符串。