Support concat_ws

velox/docs/functions/spark/string.rst

@@ -25,6 +25,25 @@ String Functions
     If ``n < 0``, the result is an empty string.
     If ``n >= 256``, the result is equivalent to chr(``n % 256``).
 
+.. spark:function:: concat_ws(separator, [string/array<string>], ...) -> varchar
+
+   Returns the concatenation result for ``string`` and all elements in ``array<string>``, separated
+   by ``separator``. The type of ``separator`` is VARCHAR. It can take variable number of remaining
+   arguments, and it allows mixed use of ``string`` and ``array<string>``. Skips NULL argument or
+   NULL array element during the concatenation. If ``separator`` is NULL, returns NULL, regardless
+   of the following inputs. For non-NULL ``separator``, if no remaining input or all remaining inputs
+   are NULL, returns an empty string. ::
+
+        SELECT concat_ws('~', 'a', 'b', 'c'); -- 'a~b~c'
+        SELECT concat_ws('~', ['a', 'b', 'c'], ['d']); -- 'a~b~c~d'
+        SELECT concat_ws('~', 'a', ['b', 'c']); -- 'a~b~c'
+        SELECT concat_ws('~', '', [''], ['a', '']); -- '~~a~'
+        SELECT concat_ws(NULL, 'a'); -- NULL
+        SELECT concat_ws('~'); -- ''
+        SELECT concat_ws('~', NULL, [NULL], 'a', 'b'); -- 'a~b'
+        SELECT concat_ws('~', NULL, NULL); -- ''
+        SELECT concat_ws('~', [NULL]); -- ''
+
 .. spark:function:: contains(left, right) -> boolean
 
     Returns true if 'right' is found in 'left'. Otherwise, returns false. ::

velox/expression/fuzzer/ExpressionFuzzer.cpp

@@ -253,6 +253,17 @@ static const std::unordered_map<
             /// them to fuzzer instead of hard-coding signatures here.
             getSignaturesForCast(),
         },
+        {
+            "concat_ws",
+            std::vector<facebook::velox::exec::FunctionSignaturePtr>{
+                // Signature: concat_ws (separator, input,...) -> output:
+                // varchar, varchar, varchar,.. -> varchar
+                facebook::velox::exec::FunctionSignatureBuilder()
+                    .argumentType("varchar")
+                    .variableArity("varchar")
+                    .returnType("varchar")
+                    .build()},
+        },
 };
 
 static std::unordered_set<std::string> splitNames(const std::string& names) {

velox/functions/sparksql/CMakeLists.txt

@@ -19,6 +19,7 @@ velox_add_library(
   ArraySort.cpp
   Bitwise.cpp
   Comparisons.cpp
+  ConcatWs.cpp
   DecimalArithmetic.cpp
   DecimalCompare.cpp
   Hash.cpp