[GitHub] [spark] lipzhu opened a new pull request #24802: [SPARK-27949][SQL]Support ANSI SQL grammar `substring(string_expression from n1 [for n2])`

[GitBox <gi...@apache.org>]

lipzhu opened a new pull request #24802: [SPARK-27949][SQL]Support ANSI SQL grammar `substring(string_expression from n1 [for n2])`
URL: https://github.com/apache/spark/pull/24802
 
 
   ## What changes were proposed in this pull request?
   
   Currently, function substr/substring's usage is like substring(string_expression, n1 [,n2]). 
   
   But the ANSI SQL defined the pattern for substr/substring is like substring(string_expression from n1 [for n2]). This gap make some inconvenient when we switch to the SparkSQL.
   
   Can we support the ANSI pattern like substring(string_expression from n1 [for n2])?
   
   http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt
   
   ## How was this patch tested?
   Pass the Jenkins with the updated test cases.

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