SEPURI-SAI-KRISHNA commented on code in PR #29123:
URL: https://github.com/apache/flink/pull/29123#discussion_r3980388040
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flink-table/flink-table-planner/src/test/scala/org/apache/flink/table/planner/expressions/ScalarFunctionsTest.scala:
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@@ -106,6 +106,26 @@ class ScalarFunctionsTest extends ScalarTypesTestBase {
// invalid length
($"f0".overlay("IS", 6, -1), "OVERLAY(f0 PLACING 'IS' FROM 6 FOR -1)",
"This IS"),
+ // a zero length replaces nothing, so the whole tail survives
+ ("abcdef".overlay("X", 2, 0), "OVERLAY('abcdef' PLACING 'X' FROM 2 FOR
0)", "aXbcdef"),
+ ("abcdef".overlay("X", 1, 0), "OVERLAY('abcdef' PLACING 'X' FROM 1 FOR
0)", "Xabcdef"),
+ ("abcdef".overlay("X", 6, 0), "OVERLAY('abcdef' PLACING 'X' FROM 6 FOR
0)", "abcdeXf"),
+
+ // a supplementary-plane character is one character and is never split
into half a pair
Review Comment:
A SQL literal can't hold an unpaired surrogate, it becomes `?` before
execution: `CHAR_LENGTH('a\ud83db')` returns 3 and the value is `a?b`. Cases
written that way would test `'a?b'`.
The function handles them: a lone surrogate counts as one code point,
`overlay("a\ud83db", "X", 1, 1)` gives `X\ud83db`. Only a direct unit test
reaches that, and there's no `SqlFunctionUtils` test class today. Add one?
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