Question

如何在PostgreSQL中计算32位循环冗余校验（CRC-32），与MySQL的方法相同？

Answer 1

你可以自己创建这个函数，这是PostgreSQL 9.6的一个工作示例

CREATE OR REPLACE FUNCTION crc32(text_string text) RETURNS bigint AS $$
DECLARE
    tmp bigint;
    i int;
    j int;
    byte_length int;
    binary_string bytea;
BEGIN
    IF text_string = '' THEN
        RETURN 0;
    END IF;

    i = 0;
    tmp = 4294967295;
    byte_length = bit_length(text_string) / 8;
    binary_string = decode(replace(text_string, E'\\\\', E'\\\\\\\\'), 'escape');
    LOOP
        tmp = (tmp # get_byte(binary_string, i))::bigint;
        i = i + 1;
        j = 0;
        LOOP
            tmp = ((tmp >> 1) # (3988292384 * (tmp & 1)))::bigint;
            j = j + 1;
            IF j >= 8 THEN
                EXIT;
            END IF;
        END LOOP;
        IF i >= byte_length THEN
            EXIT;
        END IF;
    END LOOP;
    RETURN (tmp # 4294967295);
END
$$ IMMUTABLE LANGUAGE plpgsql;

受到old post with an non crc32 accepted answer的启发。我无法从thinking sphinx找到原始代码。

Answer 2

在PG11中创建它。

文本到crc32（用于小尾数）。

结果等于java.util.zip.CRC32。

如果要crc32（t文本），可以选择crc32_update（0，t）

    create or replace function crc32_update(crc bigint, t text) returns bigint as $$
declare
    bytes bytea;
    byte bigint;
    len bigint;

    long_mask bigint = 4294967295;  -- 0xFFFFFFFF
    byte_mask integer = 255;        -- 0xFF
    rt8_mask bigint = 16777215;     -- 0xFF000000
    crc_table bigint[] = array[
        0, 1996959894, -301047508, -1727442502, 124634137, 1886057615, -379345611, -1637575261, 
        249268274, 2044508324, -522852066, -1747789432, 162941995, 2125561021, -407360249, -1866523247, 
        498536548, 1789927666, -205950648, -2067906082, 450548861, 1843258603, -187386543, -2083289657, 
        325883990, 1684777152, -43845254, -1973040660, 335633487, 1661365465, -99664541, -1928851979, 
        997073096, 1281953886, -715111964, -1570279054, 1006888145, 1258607687, -770865667, -1526024853, 
        901097722, 1119000684, -608450090, -1396901568, 853044451, 1172266101, -589951537, -1412350631, 
        651767980, 1373503546, -925412992, -1076862698, 565507253, 1454621731, -809855591, -1195530993, 
        671266974, 1594198024, -972236366, -1324619484, 795835527, 1483230225, -1050600021, -1234817731, 
        1994146192, 31158534, -1731059524, -271249366, 1907459465, 112637215, -1614814043, -390540237, 
        2013776290, 251722036, -1777751922, -519137256, 2137656763, 141376813, -1855689577, -429695999, 
        1802195444, 476864866, -2056965928, -228458418, 1812370925, 453092731, -2113342271, -183516073, 
        1706088902, 314042704, -1950435094, -54949764, 1658658271, 366619977, -1932296973, -69972891, 
        1303535960, 984961486, -1547960204, -725929758, 1256170817, 1037604311, -1529756563, -740887301, 
        1131014506, 879679996, -1385723834, -631195440, 1141124467, 855842277, -1442165665, -586318647, 
        1342533948, 654459306, -1106571248, -921952122, 1466479909, 544179635, -1184443383, -832445281, 
        1591671054, 702138776, -1328506846, -942167884, 1504918807, 783551873, -1212326853, -1061524307, 
        -306674912, -1698712650, 62317068, 1957810842, -355121351, -1647151185, 81470997, 1943803523, 
        -480048366, -1805370492, 225274430, 2053790376, -468791541, -1828061283, 167816743, 2097651377, 
        -267414716, -2029476910, 503444072, 1762050814, -144550051, -2140837941, 426522225, 1852507879, 
        -19653770, -1982649376, 282753626, 1742555852, -105259153, -1900089351, 397917763, 1622183637, 
        -690576408, -1580100738, 953729732, 1340076626, -776247311, -1497606297, 1068828381, 1219638859, 
        -670225446, -1358292148, 906185462, 1090812512, -547295293, -1469587627, 829329135, 1181335161, 
        -882789492, -1134132454, 628085408, 1382605366, -871598187, -1156888829, 570562233, 1426400815, 
        -977650754, -1296233688, 733239954, 1555261956, -1026031705, -1244606671, 752459403, 1541320221, 
        -1687895376, -328994266, 1969922972, 40735498, -1677130071, -351390145, 1913087877, 83908371, 
        -1782625662, -491226604, 2075208622, 213261112, -1831694693, -438977011, 2094854071, 198958881, 
        -2032938284, -237706686, 1759359992, 534414190, -2118248755, -155638181, 1873836001, 414664567, 
        -2012718362, -15766928, 1711684554, 285281116, -1889165569, -127750551, 1634467795, 376229701, 
        -1609899400, -686959890, 1308918612, 956543938, -1486412191, -799009033, 1231636301, 1047427035, 
        -1362007478, -640263460, 1088359270, 936918000, -1447252397, -558129467, 1202900863, 817233897, 
        -1111625188, -893730166, 1404277552, 615818150, -1160759803, -841546093, 1423857449, 601450431, 
        -1285129682, -1000256840, 1567103746, 711928724, -1274298825, -1022587231, 1510334235, 755167117
    ];

begin

    crc = ~crc;
    len = bit_length(t) / 8;
    bytes = decode(t, 'escape');

    for i in 0..len-1 loop
        byte = (get_byte(bytes, i))::bigint;
        crc = (crc >> 8 & rt8_mask) # crc_table[((crc # byte) & byte_mask) + 1];
    end loop;

    crc = ~crc;
    return crc & long_mask;
end
$$ immutable language plpgsql

CRC32功能与PL / pgSQL

2 个答案: