SQL> set numwidth 50SQL> create table test(id int);Table created.SQL> insert into test values (9999999999999999999);1 row created.SQL> select * from test;                                                ID--------------------------------------------------                               9999999999999999999

SQL> set numwidth 10SQL> select * from test;        ID----------1.0000E+19

SQL> insert into test values (9999999999999999999999999999999999999999);SQL> insert into test values (99999999999999999999999999999999999999999);SQL> select * from test;                                                ID--------------------------------------------------         9999999999999999999999999999999999999999        100000000000000000000000000000000000000000使用NUMERIC表现一样：SQL> drop table test;Table dropped.SQL> create table test(id numeric);Table created.SQL> insert into test values (9999999999999999999999999999999999999999);SQL> insert into test values (99999999999999999999999999999999999999999);SQL> select * from test;                                                ID--------------------------------------------------          9999999999999999999999999999999999999999        100000000000000000000000000000000000000000

postgres=# select 9999999999999999999999999999999999999999::numeric;                 numeric                  ------------------------------------------ 9999999999999999999999999999999999999999(1 row)postgres=# select 99999999999999999999999999999999999999999::numeric;                  numeric                  ------------------------------------------- 99999999999999999999999999999999999999999(1 row)postgres=# select 99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999::numeric;                                             numeric                                             ------------------------------------------------------------------------------------------------- 99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999(1 row)postgres=# select 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999::numeric;                                                                                                             numeric                                                                                                             --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999(1 row)postgres=# select 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999::numeric;                                                                                                                                                                                numeric                                                                                                                                                                                ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999(1 row)postgres=# select 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999998888888888888888888888888888888888888888888888888888888888888888888888888888::numeric;                                                                                                                                                                                                                                                                     numeric                                                                                                                                                                                                                                                                      -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999998888888888888888888888888888888888888888888888888888888888888888888888888888(1 row)postgres=# create table test(id numeric);CREATE TABLEpostgres=# insert into test values (9999999999999999999999999999999999999999);INSERT 0 1postgres=# insert into test values (99999999999999999999999999999999999999999);INSERT 0 1postgres=# select * from test;                    id                     -------------------------------------------  9999999999999999999999999999999999999999 99999999999999999999999999999999999999999(2 rows)postgres=# insert into test values (9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999991111111111111111111111111111111111111111111111111111111111111111111);INSERT 0 1postgres=# select * from test;                                                                                id                                                                                ------------------------------------------------------------------------------------------------------------------------------------------------------------------                                                                                                                         9999999999999999999999999999999999999999                                                                                                                        99999999999999999999999999999999999999999 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999991111111111111111111111111111111111111111111111111111111111111111111(3 rows)

/*------------------------------------------------------------------------- * * numeric.h *        Definitions for the exact numeric data type of Postgres * * Original coding 1998, Jan Wieck.  Heavily revised 2003, Tom Lane. * * Copyright (c) 1998-2010, PostgreSQL Global Development Group * * $PostgreSQL: pgsql/src/include/utils/numeric.h,v 1.29 2010/01/02 16:58:10 momjian Exp $ * *------------------------------------------------------------------------- *//* * The Numeric data type stored in the database * * NOTE: by convention, values in the packed form have been stripped of * all leading and trailing zero digits (where a "digit" is of base NBASE). * In particular, if the value is zero, there will be no digits at all! * The weight is arbitrary in that case, but we normally set it to zero. */typedef struct NumericData{        int32           vl_len_;                /* varlena header (do not touch directly!) */        uint16          n_sign_dscale;  /* Sign + display scale */        int16           n_weight;               /* Weight of 1st digit  */        char            n_data[1];              /* Digits (really array of NumericDigit) */} NumericData;typedef NumericData *Numeric;/* * Hardcoded precision limit - arbitrary, but must be small enough that * dscale values will fit in 14 bits. */#define NUMERIC_MAX_PRECISION           1000

postgres=# select 2^16 + 2^16; ?column? ----------   131072(1 row)postgres=# select repeat('9',131073)::numeric;ERROR:  22003: value overflows numeric formatLOCATION:  make_result, numeric.c:4202postgres=# select repeat('9',131072)::numeric;正常返回postgres=# select (repeat('9',131072)||'.'||repeat('9',16384))::numeric;ERROR:  22003: value overflows numeric formatLOCATION:  make_result, numeric.c:4202postgres=# select (repeat('9',131072)||'.'||repeat('9',16383))::numeric;正常返回

/* * The Numeric type as stored on disk. * * If the high bits of the first word of a NumericChoice (n_header, or * n_short.n_header, or n_long.n_sign_dscale) are NUMERIC_SHORT, then the * numeric follows the NumericShort format; if they are NUMERIC_POS or * NUMERIC_NEG, it follows the NumericLong format.  If they are NUMERIC_NAN, * it is a NaN.  We currently always store a NaN using just two bytes (i.e. * only n_header), but previous releases used only the NumericLong format, * so we might find 4-byte NaNs on disk if a database has been migrated using * pg_upgrade.  In either case, when the high bits indicate a NaN, the * remaining bits are never examined.  Currently, we always initialize these * to zero, but it might be possible to use them for some other purpose in * the future. * * In the NumericShort format, the remaining 14 bits of the header word * (n_short.n_header) are allocated as follows: 1 for sign (positive or * negative), 6 for dynamic scale, and 7 for weight.  In practice, most * commonly-encountered values can be represented this way. * * In the NumericLong format, the remaining 14 bits of the header word * (n_long.n_sign_dscale) represent the display scale; and the weight is * stored separately in n_weight. * * NOTE: by convention, values in the packed form have been stripped of * all leading and trailing zero digits (where a "digit" is of base NBASE). * In particular, if the value is zero, there will be no digits at all! * The weight is arbitrary in that case, but we normally set it to zero. */struct NumericShort{        uint16          n_header;               /* Sign + display scale + weight */        NumericDigit n_data[1];         /* Digits */};struct NumericLong{        uint16          n_sign_dscale;  /* Sign + display scale */        int16           n_weight;               /* Weight of 1st digit  */        NumericDigit n_data[1];         /* Digits */};union NumericChoice{        uint16          n_header;               /* Header word */        struct NumericLong n_long;      /* Long form (4-byte header) */        struct NumericShort n_short;    /* Short form (2-byte header) */};struct NumericData{        int32           vl_len_;                /* varlena header (do not touch directly!) */        union NumericChoice choice; /* choice of format */};

/* * make_result() - * *      Create the packed db numeric format in palloc()'d memory from *      a variable. */static Numericmake_result(NumericVar *var){        Numeric         result;        NumericDigit *digits = var->digits;        int                     weight = var->weight;        int                     sign = var->sign;        int                     n;        Size            len;        if (sign == NUMERIC_NAN)        {                result = (Numeric) palloc(NUMERIC_HDRSZ_SHORT);                SET_VARSIZE(result, NUMERIC_HDRSZ_SHORT);                result->choice.n_header = NUMERIC_NAN;                /* the header word is all we need */                dump_numeric("make_result()", result);                return result;        }        n = var->ndigits;        /* truncate leading zeroes */        while (n > 0 && *digits == 0)        {                digits++;                weight--;                n--;        }        /* truncate trailing zeroes */        while (n > 0 && digits[n - 1] == 0)                n--;        /* If zero result, force to weight=0 and positive sign */        if (n == 0)        {                weight = 0;                sign = NUMERIC_POS;        }        /* Build the result */        if (NUMERIC_CAN_BE_SHORT(var->dscale, weight))        {                len = NUMERIC_HDRSZ_SHORT + n * sizeof(NumericDigit);                result = (Numeric) palloc(len);                SET_VARSIZE(result, len);                result->choice.n_short.n_header =                        (sign == NUMERIC_NEG ? (NUMERIC_SHORT | NUMERIC_SHORT_SIGN_MASK)                         : NUMERIC_SHORT)                        | (var->dscale << NUMERIC_SHORT_DSCALE_SHIFT)                        | (weight < 0 ? NUMERIC_SHORT_WEIGHT_SIGN_MASK : 0)                        | (weight & NUMERIC_SHORT_WEIGHT_MASK);        }        else        {                len = NUMERIC_HDRSZ + n * sizeof(NumericDigit);                result = (Numeric) palloc(len);                SET_VARSIZE(result, len);                result->choice.n_long.n_sign_dscale =                        sign | (var->dscale & NUMERIC_DSCALE_MASK);                result->choice.n_long.n_weight = weight;        }        memcpy(NUMERIC_DIGITS(result), digits, n * sizeof(NumericDigit));        Assert(NUMERIC_NDIGITS(result) == n);        /* Check for overflow of int16 fields */        if (NUMERIC_WEIGHT(result) != weight ||                NUMERIC_DSCALE(result) != var->dscale)                ereport(ERROR,                                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),                                 errmsg("value overflows numeric format")));        dump_numeric("make_result()", result);        return result;}