Github user zellerh commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1046#discussion_r110060012
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -1882,6 +1882,55 @@ NABoolean HSColumnStruct::operator==(const
HSColumnStruct& other) const
return ( colnum == other.colnum );
}
+//
+// METHOD: addTruncatedColumnReference()
+//
+// PURPOSE: Generates a column reference or a SUBSTRING
+// on a column reference which truncates the
+// column to the maximum length allowed in
+// UPDATE STATISTICS.
+//
+// INPUT: 'qry' - the SQL query string to append the
+// reference to.
+// 'colInfo' - struct containing datatype info
+// about the column.
+//
+void HSColumnStruct::addTruncatedColumnReference(NAString & qry)
+ {
+ HSGlobalsClass *hs_globals = GetHSContext();
+ Lng32 maxLengthInBytes = hs_globals->maxCharColumnLengthInBytes;
+ bool isOverSized = DFS2REC::isAnyCharacter(datatype) &&
+ (length > maxLengthInBytes);
+ if (isOverSized)
+ {
+ // Note: The result data type of SUBSTRING is VARCHAR, always.
+ // But if the column is CHAR, many places in the ustat code are not
+ // expecting a VARCHAR. So, we stick a CAST around it to convert
+ // it back to a CHAR in these cases.
+
+ NABoolean isFixedChar = DFS2REC::isSQLFixedChar(datatype);
+ if (isFixedChar)
+ qry += "CAST(";
+ qry += "SUBSTRING(";
+ qry += externalColumnName->data();
+ qry += " FOR ";
+
+ char temp[20]; // big enough for "nnnnnn)"
+ sprintf(temp,"%d)", maxLengthInBytes /
CharInfo::maxBytesPerChar(charset));
+ qry += temp;
+ if (isFixedChar)
+ {
+ qry += " AS CHAR(";
+ qry += temp;
+ qry += ")";
--- End diff --
... thinking about this again, we don't have a SUBSTRING method that will
give the first n _bytes_ of a UTF-8 string, truncated to the next UTF-8
character. So, without such a function we can't really do what I suggested
above.
If we have a long UTF-8 column c and maxLengthInBytes is 256, then we will
take SUBSTRING(c for 64) here. In many situations and languages, this will be
about 64 bytes of information, not 256.
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