[IMPALA-7739] Errata in documentation of decode() method

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 3.0
• Fix Version/s: Impala 3.1.0
• Component/s: Docs
• Epic Color: ghx-label-5
• Assignee: Alexandra Rodoni
• Reporter: Paul Rogers
• Created: 22/Oct/18 20:00
• Updated: 24/Oct/18 17:37
• Resolved: 24/Oct/18 00:41

Description

Consider the description of decode() in the docs. Original text:

decode(type expression, type search1, type result1 [, type search2, type result2 ...] [, type default] )
Purpose: Compares an expression to one or more possible values, and returns a corresponding result when a match is found.

Return type: same as the initial argument value, except that integer values are promoted to BIGINT and floating-point values are promoted to DOUBLE; use CAST() when inserting into a smaller numeric column

Usage notes:

• Can be used as shorthand for a CASE expression.
• The original expression and the search expressions must of the same type or convertible types. * The result expression can be a different type, but all result expressions must be of the same type.
• Returns a successful match If the original expression is NULL and a search expression is also NULL. the
• Returns NULL if the final default value is omitted and none of the search expressions match the original expression.

Revise:

• Remove “type” prefix for arguments (here and in all functions), it really adds no value and is actually confusing because the argument is not a type, it is a value.
• Usage notes: Comparison is done using the IS NOT DISTINCT (<=>) operator: this NULL can be used as a search condition.
• Since this is a list, great between the two items in the second item in usage.
• The third item has a dangling “the” at the end.
• Reword the fourth item: “If none of the search expressions match the expression, then returns the default (if given) or NULL (if no default is given.)”

Suggested revised text:

Purpose: Compares an expression to one or more possible values using the IS NOT DISTINCT operator, and returns a corresponding result when a match is found.

Usage notes:

• Can be used as shorthand for a CASE expression.
• The expression and the search expressions must of the same type or convertible types.
• The result expression can be a different type, but all result expressions must be of the same type.
• Returns a successful match If the original expression is NULL and a search expression is also NULL. (Uses IS NOT DISTINCT to do the comparison.)
• NULL can be used as a search expression.
• Returns NULL if the final default value is omitted and none of the search expressions match the original expression.

Issue Links

• is part of: IMPALA-7747 Clean up the Expression Rewriter