#include <cctype> #include <Functions/FunctionFactory.h> #include <Functions/FunctionsHashing.h> #include <Common/StringUtils/StringUtils.h> namespace DB { /** The implementation of this algorithm is the same as most SQL language implementations. * Soundex wiki: https://en.wikipedia.org/wiki/Soundex * The details are as follows: * 1. Save the first letter. Map all occurrences of a, e, i, o, u, y, h, w. to zero(0) * 2. Replace all consonants (include the first letter) with digits as follows: * * - b, f, p, v → 1 * - c, g, j, k, q, s, x, z → 2 * - d, t → 3 * - l → 4 * - m, n → 5 * - r → 6 * * 3. Replace all adjacent same digits with one digit, and then remove all the zero (0) digits * 4. If the saved letter's digit is the same as the resulting first digit, remove the digit (keep the letter). * 5. Append 3 zeros if result contains less than 3 digits. Remove all except first letter and 3 digits after it. * */ struct SoundexImpl { static constexpr auto name = "soundex"; enum { length = 4 }; static constexpr auto soundex_map = "01230120022455012623010202"; static void skipNonAlphaASCII(const char *& start, const char * end) { while (start < end && !isAlphaASCII(*start)) ++start; } static char getScode(char c) { return soundex_map[c - 'A']; } static void apply(const char * begin, const size_t size, unsigned char * out_char_data) { const char * in_cur = begin; const char * in_end = begin + size; unsigned char * out_end = out_char_data + length; skipNonAlphaASCII(in_cur, in_end); if (in_cur < in_end) { *out_char_data++ = toUpperIfAlphaASCII(*in_cur); } char prev_code = getScode(toUpperIfAlphaASCII(*in_cur)); char ch; in_cur++; while (in_cur < in_end && out_char_data < out_end && (ch = getScode(in_cur, in_end)) != 0) { if (in_cur == in_end) { break; } in_cur++; if ((ch != '0') && (ch != last_ch)) { *out_char_data++ = ch; } last_ch = ch; } while (out_char_data < out_end) { *out_char_data++ = '0'; } return; } }; REGISTER_FUNCTION(Soundex) { factory.registerFunction<FunctionStringHashFixedString<SoundexImpl>>( Documentation{"Returns soundex code of a string."}, FunctionFactory::CaseInsensitive); } }