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Add functions to generate random numbers in a specified range.
This adds 3 new variants of the random() function: random(min integer, max integer) returns integer random(min bigint, max bigint) returns bigint random(min numeric, max numeric) returns numeric Each returns a random number x in the range min <= x <= max. For the numeric function, the number of digits after the decimal point is equal to the number of digits that "min" or "max" has after the decimal point, whichever has more. The main entry points for these functions are in a new C source file. The existing random(), random_normal(), and setseed() functions are moved there too, so that they can all share the same PRNG state, which is kept private to that file. Dean Rasheed, reviewed by Jian He, David Zhang, Aleksander Alekseev, and Tomas Vondra. Discussion: https://postgr.es/m/CAEZATCV89Vxuq93xQdmc0t-0Y2zeeNQTdsjbmV7dyFBPykbV4Q@mail.gmail.com
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-101
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‎doc/src/sgml/func.sgml

+38-5
Original file line numberDiff line numberDiff line change
@@ -1862,6 +1862,39 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>random</primary>
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</indexterm>
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<function>random</function> ( <parameter>min</parameter> <type>integer</type>, <parameter>max</parameter> <type>integer</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para role="func_signature">
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<function>random</function> ( <parameter>min</parameter> <type>bigint</type>, <parameter>max</parameter> <type>bigint</type> )
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<returnvalue>bigint</returnvalue>
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</para>
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<para role="func_signature">
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<function>random</function> ( <parameter>min</parameter> <type>numeric</type>, <parameter>max</parameter> <type>numeric</type> )
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<returnvalue>numeric</returnvalue>
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</para>
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<para>
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Returns a random value in the range
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<parameter>min</parameter> &lt;= x &lt;= <parameter>max</parameter>.
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For type <type>numeric</type>, the result will have the same number of
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fractional decimal digits as <parameter>min</parameter> or
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<parameter>max</parameter>, whichever has more.
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</para>
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<para>
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<literal>random(1, 10)</literal>
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<returnvalue>7</returnvalue>
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</para>
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<para>
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<literal>random(-0.499, 0.499)</literal>
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<returnvalue>0.347</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
@@ -1906,19 +1939,19 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
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</table>
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<para>
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The <function>random()</function> function uses a deterministic
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pseudo-random number generator.
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The <function>random()</function> and <function>random_normal()</function>
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functions listed in <xref linkend="functions-math-random-table"/> use a
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deterministic pseudo-random number generator.
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It is fast but not suitable for cryptographic
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applications; see the <xref linkend="pgcrypto"/> module for a more
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secure alternative.
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If <function>setseed()</function> is called, the series of results of
1915-
subsequent <function>random()</function> calls in the current session
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subsequent calls to these functions in the current session
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can be repeated by re-issuing <function>setseed()</function> with the same
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argument.
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Without any prior <function>setseed()</function> call in the same
1919-
session, the first <function>random()</function> call obtains a seed
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session, the first call to any of these functions obtains a seed
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from a platform-dependent source of random bits.
1921-
These remarks hold equally for <function>random_normal()</function>.
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</para>
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<para>

‎src/backend/utils/adt/Makefile

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@@ -82,6 +82,7 @@ OBJS = \
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pg_lsn.o \
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pg_upgrade_support.o \
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pgstatfuncs.o \
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pseudorandomfuncs.o \
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pseudotypes.o \
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quote.o \
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rangetypes.o \

‎src/backend/utils/adt/float.c

-95
Original file line numberDiff line numberDiff line change
@@ -21,10 +21,8 @@
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#include "catalog/pg_type.h"
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#include "common/int.h"
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#include "common/pg_prng.h"
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#include "common/shortest_dec.h"
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#include "libpq/pqformat.h"
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#include "miscadmin.h"
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#include "utils/array.h"
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#include "utils/float.h"
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#include "utils/fmgrprotos.h"
@@ -64,10 +62,6 @@ float8 degree_c_sixty = 60.0;
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float8 degree_c_one_half = 0.5;
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float8 degree_c_one = 1.0;
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/* State for drandom() and setseed() */
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static bool drandom_seed_set = false;
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static pg_prng_state drandom_seed;
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/* Local function prototypes */
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static double sind_q1(double x);
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static double cosd_q1(double x);
@@ -2785,95 +2779,6 @@ derfc(PG_FUNCTION_ARGS)
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}
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27872781

2788-
/* ========== RANDOM FUNCTIONS ========== */
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2790-
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/*
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* initialize_drandom_seed - initialize drandom_seed if not yet done
2793-
*/
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static void
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initialize_drandom_seed(void)
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{
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/* Initialize random seed, if not done yet in this process */
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if (unlikely(!drandom_seed_set))
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{
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/*
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* If possible, initialize the seed using high-quality random bits.
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* Should that fail for some reason, we fall back on a lower-quality
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* seed based on current time and PID.
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*/
2805-
if (unlikely(!pg_prng_strong_seed(&drandom_seed)))
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{
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TimestampTz now = GetCurrentTimestamp();
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uint64 iseed;
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2810-
/* Mix the PID with the most predictable bits of the timestamp */
2811-
iseed = (uint64) now ^ ((uint64) MyProcPid << 32);
2812-
pg_prng_seed(&drandom_seed, iseed);
2813-
}
2814-
drandom_seed_set = true;
2815-
}
2816-
}
2817-
2818-
/*
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* drandom - returns a random number
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*/
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Datum
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drandom(PG_FUNCTION_ARGS)
2823-
{
2824-
float8 result;
2825-
2826-
initialize_drandom_seed();
2827-
2828-
/* pg_prng_double produces desired result range [0.0 - 1.0) */
2829-
result = pg_prng_double(&drandom_seed);
2830-
2831-
PG_RETURN_FLOAT8(result);
2832-
}
2833-
2834-
/*
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* drandom_normal - returns a random number from a normal distribution
2836-
*/
2837-
Datum
2838-
drandom_normal(PG_FUNCTION_ARGS)
2839-
{
2840-
float8 mean = PG_GETARG_FLOAT8(0);
2841-
float8 stddev = PG_GETARG_FLOAT8(1);
2842-
float8 result,
2843-
z;
2844-
2845-
initialize_drandom_seed();
2846-
2847-
/* Get random value from standard normal(mean = 0.0, stddev = 1.0) */
2848-
z = pg_prng_double_normal(&drandom_seed);
2849-
/* Transform the normal standard variable (z) */
2850-
/* using the target normal distribution parameters */
2851-
result = (stddev * z) + mean;
2852-
2853-
PG_RETURN_FLOAT8(result);
2854-
}
2855-
2856-
/*
2857-
* setseed - set seed for the random number generator
2858-
*/
2859-
Datum
2860-
setseed(PG_FUNCTION_ARGS)
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{
2862-
float8 seed = PG_GETARG_FLOAT8(0);
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2864-
if (seed < -1 || seed > 1 || isnan(seed))
2865-
ereport(ERROR,
2866-
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
2867-
errmsg("setseed parameter %g is out of allowed range [-1,1]",
2868-
seed)));
2869-
2870-
pg_prng_fseed(&drandom_seed, seed);
2871-
drandom_seed_set = true;
2872-
2873-
PG_RETURN_VOID();
2874-
}
2875-
2876-
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/*
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* =========================

‎src/backend/utils/adt/meson.build

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@@ -69,6 +69,7 @@ backend_sources += files(
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'pg_lsn.c',
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'pg_upgrade_support.c',
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'pgstatfuncs.c',
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'pseudorandomfuncs.c',
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'pseudotypes.c',
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'quote.c',
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'rangetypes.c',

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