implement function ascii

docs/en/sql-reference/functions/string-functions.md

@@ -1150,3 +1150,13 @@ A text with tags .
 The content within <b>CDATA</b>
 Do Nothing for 2 Minutes 2:00 &nbsp;
 ```
+
+## ascii(s) {#ascii}
+
+Returns the ASCII code point of the first character of str.  The result type is Int32.
+
+If s is empty, the result is 0. If the first character is not an ASCII character or part of the Latin-1 Supplement range of UTF-16, the result is undefined.
+
+
+
+

src/Functions/ascii.cpp

@@ -0,0 +1,74 @@
+#include <DataTypes/DataTypeString.h>
+#include <Functions/FunctionFactory.h>
+#include <Functions/FunctionStringOrArrayToT.h>
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
+    extern const int NOT_IMPLEMENTED;
+}
+
+struct AsciiName
+{
+    static constexpr auto name = "ascii";
+};
+
+
+struct AsciiImpl
+{
+    static constexpr auto is_fixed_to_constant = false;
+    using ReturnType = Int32;
+
+
+    static void vector(const ColumnString::Chars & data, const ColumnString::Offsets & offsets, PaddedPODArray<ReturnType> & res)
+    {
+        size_t size = offsets.size();
+
+        ColumnString::Offset prev_offset = 0;
+        for (size_t i = 0; i < size; ++i)
+        {
+            res[i] = doAscii(data, prev_offset, offsets[i] - prev_offset - 1);
+            prev_offset = offsets[i];
+        }
+    }
+
+    [[noreturn]] static void vectorFixedToConstant(const ColumnString::Chars &  /*data*/, size_t  /*n*/, Int32 &  /*res*/)
+    {
+        throw Exception("vectorFixedToConstant not implemented for function " + std::string(AsciiName::name), ErrorCodes::NOT_IMPLEMENTED);
+    }
+
+    static void vectorFixedToVector(const ColumnString::Chars & data, size_t n, PaddedPODArray<ReturnType> & res)
+    {
+        size_t size = data.size() / n;
+
+        for (size_t i = 0; i < size; ++i)
+        {
+            res[i] = doAscii(data, i * n, n);
+        }
+    }
+
+    [[noreturn]] static void array(const ColumnString::Offsets & /*offsets*/, PaddedPODArray<ReturnType> & /*res*/)
+    {
+        throw Exception("Cannot apply function " + std::string(AsciiName::name) + " to Array argument", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
+    }
+
+    [[noreturn]] static void uuid(const ColumnUUID::Container & /*offsets*/, size_t /*n*/, PaddedPODArray<ReturnType> & /*res*/)
+    {
+        throw Exception("Cannot apply function " + std::string(AsciiName::name) + " to UUID argument", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
+    }
+
+private:
+    static Int32 doAscii(const ColumnString::Chars & buf, size_t offset, size_t size) { return size ? static_cast<ReturnType>(buf[offset]) : 0; }
+};
+
+using FunctionAscii = FunctionStringOrArrayToT<AsciiImpl, AsciiName, AsciiImpl::ReturnType>;
+
+REGISTER_FUNCTION(Ascii)
+{
+    factory.registerFunction<FunctionAscii>({}, FunctionFactory::CaseInsensitive);
+}
+
+}

tests/queries/0_stateless/02353_ascii.reference

@@ -0,0 +1,2 @@
+50
+0

tests/queries/0_stateless/02353_ascii.sql

@@ -0,0 +1,2 @@
+SELECT ascii('234');
+SELECT ascii('');