“创建自定义类型”

// Encode: string -> binary. Write to out.buffer() and call out.set_length(n).
void mytype_from_string(std::string_view from, vsql::CustomResult out) { /* ... */ }

// Decode: binary -> string. Write to out.buffer() and call out.set_length(n).
void mytype_to_string(vsql::CustomArg in, vsql::StringResult out) { /* ... */ }

// Compare: returns <0, 0, or >0.
int mytype_compare(vsql::CustomArg a, vsql::CustomArg b) { /* ... */ }

// Hash: returns hash code (optional).
size_t mytype_hash(vsql::CustomArg in) { /* ... */ }

#include <villagesql/vsql.h>

using namespace vsql;

// Required for auto-generating VDF names at compile time.
static constexpr const char kMyTypeName[] = "MYTYPE";

constexpr auto MYTYPE =
    vsql::make_type<kMyTypeName>()
        .persisted_length(16)
        .max_decode_buffer_length(64)
        .from_string<&mytype_from_string>()   // auto: "MYTYPE::from_string"
        .to_string<&mytype_to_string>()       // auto: "MYTYPE::to_string"
        .compare<&mytype_compare>()           // auto: "MYTYPE::compare"
        .hash<&mytype_hash>()                 // optional; auto: "MYTYPE::hash"
        .intrinsic_default_str("...")         // must encode to exactly 16 bytes; see Development guide
        .build();

VEF_GENERATE_ENTRY_POINTS(
    make_extension()
        .type(MYTYPE)
);

-- Convert string to custom type (calls MYTYPE::from_string)
SELECT MYTYPE::from_string('(1.0,2.0)');

-- Convert custom type to string (calls MYTYPE::to_string)
SELECT MYTYPE::to_string(my_column) FROM my_table;

-- Explicit conversion in INSERT
INSERT INTO my_table (id, value)
VALUES (1, MYTYPE::from_string('(3.0,4.0)'));

UPDATE my_table
SET val = MYTYPE::from_string(
  CASE (pk MOD 2)
    WHEN 0 THEN '(1.0,2.0)'
    ELSE '(0.0,0.0)'
  END
);

#include <cstdio>
#include <cstring>
#include <villagesql/vsql.h>

using namespace vsql;

// Encode: "(real,imag)" string -> 16 bytes little-endian
void encode_complex(std::string_view from, CustomResult out) {
    auto buf = out.buffer();
    if (buf.size() < 16) return;
    double real, imag;
    if (sscanf(from.data(), "(%lf,%lf)", &real, &imag) != 2) {
        out.warning("invalid complex format: expected (real,imag)");
        return;
    }
    memcpy(buf.data(), &real, 8);
    memcpy(buf.data() + 8, &imag, 8);
    out.set_length(16);
}

// Decode: 16 bytes -> "(real,imag)" string
void decode_complex(CustomArg in, StringResult out) {
    auto data = in.value();
    if (data.size() < 16) return;
    double real, imag;
    memcpy(&real, data.data(), 8);
    memcpy(&imag, data.data() + 8, 8);
    auto buf = out.buffer();
    int len = snprintf(buf.data(), buf.size(), "(%.6f,%.6f)", real, imag);
    if (len < 0 || static_cast<size_t>(len) >= buf.size()) return;
    out.set_length(static_cast<size_t>(len));
}

// Compare for ORDER BY: real part first, then imaginary
int compare_complex(CustomArg a, CustomArg b) {
    auto da = a.value();
    auto db = b.value();
    if (da.size() < 16 || db.size() < 16) return 0;
    double a_real, a_imag, b_real, b_imag;
    memcpy(&a_real, da.data(), 8);
    memcpy(&a_imag, da.data() + 8, 8);
    memcpy(&b_real, db.data(), 8);
    memcpy(&b_imag, db.data() + 8, 8);
    if (a_real < b_real) return -1;
    if (a_real > b_real) return 1;
    if (a_imag < b_imag) return -1;
    if (a_imag > b_imag) return 1;
    return 0;
}

CREATE TABLE signals (
    id INT PRIMARY KEY,
    impedance COMPLEX,
    frequency_response COMPLEX
);

INSERT INTO signals VALUES (1, '(50.0,10.0)', '(0.95,0.31)');

-- ORDER BY works because we provided compare_complex!
SELECT * FROM signals ORDER BY impedance;

-- Prepared statements work with custom types
PREPARE stmt FROM 'SELECT * FROM signals WHERE impedance = ?';
SET @val = '(50.0,10.0)';
EXECUTE stmt USING @val;

-- Aggregate operations work with custom types
SELECT COUNT(DISTINCT impedance), MIN(impedance), MAX(impedance),
       GROUP_CONCAT(impedance ORDER BY impedance) FROM signals;

CREATE TABLE signals (
    id INT PRIMARY KEY,
    impedance COMPLEX,
    -- Generated column computed by a VDF
    magnitude DOUBLE GENERATED ALWAYS AS (complex_abs(impedance)) STORED
);

CREATE TABLE signals (
    id INT PRIMARY KEY,
    sig COMPLEX,
    INDEX idx_magnitude ((COMPLEX_ABS(sig)))
);

SELECT id FROM signals WHERE COMPLEX_ABS(sig) > CAST(20.0 AS DOUBLE);