ivan
mysqlcompat-0.0.7是网上开源的postgresql兼容包；
以下是写sql兼容的方式，兼容mysql函数，此种方式效率会是瓶颈；
因此尽量改成postgresql原生的函数或者底层源码兼容；
1 -- ATAN2()
-- Two parameter alias of atan2
CREATE OR REPLACE FUNCTION atan(double precision, double precision)
RETURNS double precision AS $$
SELECT pg_catalog.atan2($1, $2)
$$ IMMUTABLE STRICT LANGUAGE SQL;
2 -- CRC32()
CREATE OR REPLACE FUNCTION crc32(text)
RETURNS bigint AS $$
DECLARE
-- crc look up table
-- based on the polynomial:
-- x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1
crc_lu bigint[256] := ARRAY[0, 1996959894, 3993919788, 2567524794,
124634137, 1886057615, 3915621685, 2657392035, 249268274, 2044508324,
3772115230, 2547177864, 162941995, 2125561021, 3887607047, 2428444049,
498536548, 1789927666, 4089016648, 2227061214, 450548861, 1843258603,
4107580753, 2211677639, 325883990, 1684777152, 4251122042,
2321926636, 335633487, 1661365465, 4195302755, 2366115317,
997073096, 1281953886, 3579855332, 2724688242, 1006888145,
1258607687, 3524101629, 2768942443, 901097722, 1119000684,
3686517206, 2898065728, 853044451, 1172266101, 3705015759,
2882616665, 651767980, 1373503546, 3369554304, 3218104598,
565507253, 1454621731, 3485111705, 3099436303, 671266974,
1594198024, 3322730930, 2970347812, 795835527, 1483230225,
3244367275, 3060149565, 1994146192, 31158534, 2563907772,
4023717930, 1907459465, 112637215, 2680153253, 3904427059,
2013776290, 251722036, 2517215374, 3775830040, 2137656763,
141376813, 2439277719, 3865271297, 1802195444, 476864866,
2238001368, 4066508878, 1812370925, 453092731, 2181625025,
4111451223, 1706088902, 314042704, 2344532202, 4240017532,
1658658271, 366619977, 2362670323, 4224994405, 1303535960,
984961486, 2747007092, 3569037538, 1256170817, 1037604311,
2765210733, 3554079995, 1131014506, 879679996, 2909243462,
3663771856, 1141124467, 855842277, 2852801631, 3708648649,
1342533948, 654459306, 3188396048, 3373015174, 1466479909,
544179635, 3110523913, 3462522015, 1591671054, 702138776,
2966460450, 3352799412, 1504918807, 783551873, 3082640443,
3233442989, 3988292384, 2596254646, 62317068, 1957810842,
3939845945, 2647816111, 81470997, 1943803523, 3814918930,
2489596804, 225274430, 2053790376, 3826175755, 2466906013,
167816743, 2097651377, 4027552580, 2265490386, 503444072,
1762050814, 4150417245, 2154129355, 426522225, 1852507879,
4275313526, 2312317920, 282753626, 1742555852, 4189708143,
2394877945, 397917763, 1622183637, 3604390888, 2714866558,
953729732, 1340076626, 3518719985, 2797360999, 1068828381,
1219638859, 3624741850, 2936675148, 906185462, 1090812512,
3747672003, 2825379669, 829329135, 1181335161, 3412177804,
3160834842, 628085408, 1382605366, 3423369109, 3138078467,
570562233, 1426400815, 3317316542, 2998733608, 733239954,
1555261956, 3268935591, 3050360625, 752459403, 1541320221,
2607071920, 3965973030, 1969922972, 40735498, 2617837225,
3943577151, 1913087877, 83908371, 2512341634, 3803740692,
2075208622, 213261112, 2463272603, 3855990285, 2094854071,
198958881, 2262029012, 4057260610, 1759359992, 534414190,
2176718541, 4139329115, 1873836001, 414664567, 2282248934,
4279200368, 1711684554, 285281116, 2405801727, 4167216745,
1634467795, 376229701, 2685067896, 3608007406, 1308918612,
956543938, 2808555105, 3495958263, 1231636301, 1047427035,
2932959818, 3654703836, 1088359270, 936918000, 2847714899,
3736837829, 1202900863, 817233897, 3183342108, 3401237130,
1404277552, 615818150, 3134207493, 3453421203, 1423857449,
601450431, 3009837614, 3294710456, 1567103746, 711928724,
3020668471, 3272380065, 1510334235, 755167117];
crc bigint := 4294967295; -- must use bigint, because we don't have
-- an unsigned int32
len int;
data ALIAS FOR $1;
tmp bigint;
pos int := 1;
c text;
d bigint;
BEGIN
len = pg_catalog.length(data);
WHILE len >= pos LOOP
c := SUBSTRING(data FROM pos FOR 1);
d := pg_catalog.ascii(c);
pos = pos + 1;
tmp = (crc # d) & 255;
crc = crc_lu[tmp + 1] # (crc >> 8);
END LOOP;
crc := crc # 4294967295;
RETURN crc;
END
$$ IMMUTABLE STRICT LANGUAGE plpgsql;
3 -- FORMAT()
-- FIXME: Only handles numbers with integer part up to 21 digits
--
-- MySQL has some bugs with long numbers, but they're not worth replicating:
-- format(9999999999999999999999999999999999999999999999999999999999999999, 10)
-- --> last group has four nines!
-- format(9999999999999999999999999999999999999999999999999999999999999999999999999, 1);
-- --> last group has five nines and no decmial zero
CREATE OR REPLACE FUNCTION format(numeric, integer)
RETURNS text AS $$
SELECT pg_catalog.to_char(pg_catalog.round($1, $2), 'FM999,999,999,999,999,999,990'
operator(pg_catalog.||)
case when $2 > 0 then
'.' operator(pg_catalog.||) pg_catalog.repeat('0', $2)
else '' end)
$$ IMMUTABLE STRICT LANGUAGE SQL;
4 -- LN(), LOG()
-- Not reimplemented but note that PostgreSQL has an error on -ve values,
-- but MySQL just returns NULL.
5 -- LOG2()
CREATE OR REPLACE FUNCTION log2(numeric)
RETURNS numeric AS $$
SELECT CASE WHEN $1 > 0 THEN pg_catalog.log(2, $1) ELSE NULL END
$$ IMMUTABLE STRICT LANGUAGE SQL;
6 -- LOG10()
CREATE OR REPLACE FUNCTION log10(numeric)
RETURNS numeric AS $$
SELECT CASE WHEN $1 > 0 THEN pg_catalog.log(10, $1) ELSE NULL END
$$ IMMUTABLE STRICT LANGUAGE SQL;
7 -- MOD()
-- PostgreSQL has all MOD usage the same as MySQL EXCEPT this will not work:
--
-- SELECT 29 MOD 9;
8 -- RAND()
CREATE OR REPLACE FUNCTION rand() RETURNS double precision AS $$
SELECT pg_catalog.random()
$$ VOLATILE LANGUAGE SQL;
CREATE OR REPLACE FUNCTION rand(integer) RETURNS double precision AS $$
SELECT pg_catalog.setseed($1);
SELECT pg_catalog.random()
$$ VOLATILE LANGUAGE SQL;
9 -- SQRT()
-- Not reimplemented but note that PostgreSQL has an error on -ve values,
-- but MySQL just returns NULL.
10 -- TRUNCATE()
CREATE OR REPLACE FUNCTION truncate(numeric, integer)
RETURNS numeric AS $$
SELECT pg_catalog.trunc($1, $2)
$$ IMMUTABLE STRICT LANGUAGE SQL;
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