IMPALA-7575: [DOCS] FMOD() is not the same as the % operator - Removed the text about FMOD being equivalent to %. - Added a note that MOD will show as % in the query plan.
Change-Id: I3b02d3e3f556d93e1d651eaee12217d6b0e3f9e0 Reviewed-on: http://gerrit.cloudera.org:8080/11586 Reviewed-by: Tim Armstrong <tarmstr...@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com> Project: http://git-wip-us.apache.org/repos/asf/impala/repo Commit: http://git-wip-us.apache.org/repos/asf/impala/commit/80edf370 Tree: http://git-wip-us.apache.org/repos/asf/impala/tree/80edf370 Diff: http://git-wip-us.apache.org/repos/asf/impala/diff/80edf370 Branch: refs/heads/master Commit: 80edf37010884d6aa7edae818d8219918ea0809e Parents: 3fabc2d Author: Alex Rodoni <arod...@cloudera.com> Authored: Thu Oct 4 15:44:49 2018 -0700 Committer: Alex Rodoni <arod...@cloudera.com> Committed: Thu Oct 4 23:11:07 2018 +0000 ---------------------------------------------------------------------- docs/topics/impala_math_functions.xml | 95 ++++++++++++++---------------- 1 file changed, 45 insertions(+), 50 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/impala/blob/80edf370/docs/topics/impala_math_functions.xml ---------------------------------------------------------------------- diff --git a/docs/topics/impala_math_functions.xml b/docs/topics/impala_math_functions.xml index 7961a11..b4f97c5 100644 --- a/docs/topics/impala_math_functions.xml +++ b/docs/topics/impala_math_functions.xml @@ -446,26 +446,23 @@ select factorial(-100); <dd> <indexterm audience="hidden">fmod() function</indexterm> - <b>Purpose:</b> Returns the modulus of a floating-point number. Equivalent to the <codeph>%</codeph> arithmetic operator. - <p> - <b>Return type:</b> <codeph>float</codeph> or <codeph>double</codeph>, depending on type of arguments - </p> + <b>Purpose:</b> Returns the modulus of a floating-point number.<p> + <b>Return type:</b> + <codeph>float</codeph> or <codeph>double</codeph>, depending on type + of arguments </p> <p conref="../shared/impala_common.xml#common/added_in_111"/> <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> - <p> - Because this function operates on <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph> - values, it is subject to potential rounding errors for values that cannot be - represented precisely. Prefer to use whole numbers, or values that you know - can be represented precisely by the <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph> - types. - </p> + <p> Because this function operates on <codeph>DOUBLE</codeph> or + <codeph>FLOAT</codeph> values, it is subject to potential rounding + errors for values that cannot be represented precisely. Prefer to + use whole numbers, or values that you know can be represented + precisely by the <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph> + types. </p> <p conref="../shared/impala_common.xml#common/example_blurb"/> - <p> - The following examples show equivalent operations with the <codeph>fmod()</codeph> - function and the <codeph>%</codeph> arithmetic operator, for values not subject - to any rounding error. - </p> -<codeblock>select fmod(10,3); + <p> The following examples show equivalent operations with the + <codeph>fmod()</codeph> function and the <codeph>%</codeph> + arithmetic operator, for values not subject to any rounding error. </p> + <codeblock>select fmod(10,3); +-------------+ | fmod(10, 3) | +-------------+ @@ -493,17 +490,16 @@ select 5.5 % 2; | 1.5 | +---------+ </codeblock> - <p> - The following examples show operations with the <codeph>fmod()</codeph> - function for values that cannot be represented precisely by the - <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph> types, and thus are - subject to rounding error. <codeph>fmod(9.9,3.0)</codeph> returns a value - slightly different than the expected 0.9 because of rounding. - <codeph>fmod(9.9,3.3)</codeph> returns a value quite different from - the expected value of 0 because of rounding error during intermediate - calculations. - </p> -<codeblock>select fmod(9.9,3.0); + <p> The following examples show operations with the + <codeph>fmod()</codeph> function for values that cannot be + represented precisely by the <codeph>DOUBLE</codeph> or + <codeph>FLOAT</codeph> types, and thus are subject to rounding + error. <codeph>fmod(9.9,3.0)</codeph> returns a value slightly + different than the expected 0.9 because of rounding. + <codeph>fmod(9.9,3.3)</codeph> returns a value quite different + from the expected value of 0 because of rounding error during + intermediate calculations. </p> + <codeblock>select fmod(9.9,3.0); +--------------------+ | fmod(9.9, 3.0) | +--------------------+ @@ -826,31 +822,30 @@ select fmod(9.9,3.3); <dd rev="2.2.0"> <indexterm audience="hidden">mod() function</indexterm> - <b>Purpose:</b> Returns the modulus of a number. Equivalent to the <codeph>%</codeph> arithmetic operator. - Works with any size integer type, any size floating-point type, and <codeph>DECIMAL</codeph> - with any precision and scale. - <p conref="../shared/impala_common.xml#common/return_type_same"/> + <b>Purpose:</b> Returns the modulus of a number. Equivalent to the + <codeph>%</codeph> arithmetic operator. Works with any size integer + type, any size floating-point type, and <codeph>DECIMAL</codeph> with + any precision and scale. <p + conref="../shared/impala_common.xml#common/return_type_same"/> <p conref="../shared/impala_common.xml#common/added_in_220"/> <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> - <p> - Because this function works with <codeph>DECIMAL</codeph> values, prefer it over <codeph>fmod()</codeph> - when working with fractional values. It is not subject to the rounding errors that make - <codeph>fmod()</codeph> problematic with floating-point numbers. - The <codeph>%</codeph> arithmetic operator now uses the <codeph>mod()</codeph> function - in cases where its arguments can be interpreted as <codeph>DECIMAL</codeph> values, - increasing the accuracy of that operator. - </p> + <p> Because this function works with <codeph>DECIMAL</codeph> values, + prefer it over <codeph>fmod()</codeph> when working with fractional + values. It is not subject to the rounding errors that make + <codeph>fmod()</codeph> problematic with floating-point + numbers.</p><p rev="IMPALA-6202">Query plans shows the + <codeph>MOD()</codeph> function as the <codeph>%</codeph> + operator.</p> <p conref="../shared/impala_common.xml#common/example_blurb"/> - <p> - The following examples show how the <codeph>mod()</codeph> function works for - whole numbers and fractional values, and how the <codeph>%</codeph> operator - works the same way. In the case of <codeph>mod(9.9,3)</codeph>, - the type conversion for the second argument results in the first argument - being interpreted as <codeph>DOUBLE</codeph>, so to produce an accurate - <codeph>DECIMAL</codeph> result requires casting the second argument - or writing it as a <codeph>DECIMAL</codeph> literal, 3.0. - </p> -<codeblock>select mod(10,3); + <p> The following examples show how the <codeph>mod()</codeph> + function works for whole numbers and fractional values, and how the + <codeph>%</codeph> operator works the same way. In the case of + <codeph>mod(9.9,3)</codeph>, the type conversion for the second + argument results in the first argument being interpreted as + <codeph>DOUBLE</codeph>, so to produce an accurate + <codeph>DECIMAL</codeph> result requires casting the second + argument or writing it as a <codeph>DECIMAL</codeph> literal, 3.0. </p> + <codeblock>select mod(10,3); +-------------+ | fmod(10, 3) | +-------------+
