[GitHub] [trafodion] liuyu000 commented on a change in pull request #1837: [TRAFODION-3306] Add the TRUNC Function in the Trafodion SQL Reference Manual

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liuyu000 commented on a change in pull request #1837: [TRAFODION-3306] Add the TRUNC Function in the Trafodion SQL Reference Manual
URL: https://github.com/apache/trafodion/pull/1837#discussion_r278786551
 
 

 ##########
 File path: docs/sql_reference/src/asciidoc/_chapters/sql_functions_and_expressions.adoc
 ##########
 @@ -12460,6 +12460,122 @@ CHAR(20). This expression uses the TRIM function to return the value
 TRIM(first_name) || ' ' || TRIM (last_name)
 ```
 
+[[trunc_function]]
+== TRUNC Function
+
+The TRUNC (TRUNCATE) function truncates `_numeric-expression_` on an optional `_decimal-place_` decimal position(s), that is, it rounds down `_numeric-expression_` to the nearest (or equal) integer closer to zero *without rounding*.
+
+TRUNC is a Trafodion SQL extension.
+
+`TRUNC (_numeric-expression_[, _decimal-place_])`
+
+[[syntax_descriptions_of_trunc]]
+=== Syntax Descriptions of TRUNC
+
+* `_numeric-expression_`
+
++
+is an SQL numeric expression to be truncated.
+
++
+For more information, see <<numeric_value_expressions,Numeric Value Expressions>>.
+
+* `_decimal-place_`
+
++
+is an integer specifying the precision of the truncation.
+
+NOTE: `_numeric-expression_` and `_decimal-place_` cannot be NULL.
+
+NOTE: Currently, `_decimal-place_` can be zero or a positive integer, while *negative integer* is *not supported*.
+ 
+NOTE: If `_decimal-place_` is omitted, `_numeric-expression_` is truncated to zero decimal position, which means all digits after the decimal point are removed. 
+
+*Example*
+
+```
+SELECT TRUNC (-1.2345), TRUNC (1.2345) FROM DUAL
+
+(EXPR)       (EXPR)     
+-----------  -----------
+
+         -1            1
+
+--- 1 row(s) selected.
+```
+
+NOTE: If `_decimal-place_` is a positive integer, `_numeric-expression_` is truncated to `_decimal-place_` decimal position(s) to the right of the decimal point. +
+*Example* +
+1 for truncating to a multiple of 0.1 +
+2 for truncating to a multiple of 0.01 +
+3 for truncating to a multiple of 0.001 +
+
+*Example*
+
+```
+SELECT TRUNC (1.2345,1), TRUNC (1.2345,2), TRUNC (1.2345, 3), TRUNC (1.2345, 4) FROM DUAL;
+
+(EXPR)        (EXPR)        (EXPR)        (EXPR)      
+------------  ------------  ------------  ------------ 
+
+         1.2          1.23         1.234        1.2345
+
+--- 1 row(s) selected.
+```
+
+NOTE: `_decimal-place_` cannot be larger than the number of decimal digits.
+
+[[considerations_for_trunc]]
+=== Considerations for TRUNC
+
+* Trafodion provides the <<ceil_function, CEIL Function>>, the <<floor_function, FLOOR Function>>, the <<round_function, ROUND Function>> and the <<trunc_function, TRUNC Function>> to round numbers, these functions can be interchanged in certain circumstances.
+
++
+*Example*
+
++
+|===
+
+^| *Condition*  ^| *Result*
+
+| All of the following conditions for the TRUNC function are true： +
+  &#9702; `_numeric-expression_` is *greater* than zero +
+  &#9702; `_decimal-place_` is not specified 
+
+| *TRUNC* function = *FLOOR* function
+
+| All of the following conditions for the TRUNC function are true： +
+  &#9702; `_numeric-expression_` is *less* than zero +
+  &#9702; `_decimal-place_` is not specified 
+
+| *TRUNC* function = *CEIL* function
+
+|===
+
+* The TRUNC function is similar to the ROUND function in terms of *reducing the number of decimal places*. 
+
++
+However, the TRUNC function *does not perform any rounding* as the ROUND function does.
 
 Review comment:
   @DaveBirdsall Thank you, I've incorporated your comment. 

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