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[面试相关] 数据库面试题集 英文的

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发表于 2015-6-1 11:47:22 | 显示全部楼层 |阅读模式
Question: Log Table, What is log table? What is the use of log table?
Answer:The Error Table contains information concerning:
- Data conversion errors Constraint violations and other error conditions:
Contains rows which failed to be manupulated due to constraint violations or Transalation error
Captures rows that contains duplicate Values for UPIs.
It logs errors & exceptions that occurs during the apply phase.
It logs errors that are occurs during the acquisition phase.
what is basic teradata query language?
BTEQ(Basic teradata query)
It allows us to write SQL Statements along with BTEQ commands. We can use BTEQ for importing,exporting and reporting purposes.
The commands start with a (.) dot  and can be terminated by using (;), it is not mandatory to use (;). SQL statements doesnt start with a dot , but (;) is compulsary to terminate the SQL statement.
BTEQ will assume any thing written with out a dot as a sql statement and requires a (;) to terminate it.
How teradata makes sure that there are no duplicate rows being inserted when its a SET table?
Teradata will redirect the new inserted row as per its PI to the target AMP (on the basis of its row hash value), and if it find same row hash value in that
AMP (hash synonyms) then it start comparing the whole row, and find out if duplicate.
If its a duplicate it silently skips it without throwing any error
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