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Loss of decimal digits when converting from REAL to DECIMAL #129

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Loss of decimal digits when converting from REAL to DECIMAL #129

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11 changes: 10 additions & 1 deletion src/backend/utils/adt/numeric.c
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@
#include "utils/numeric.h"
#include "utils/pg_lsn.h"
#include "utils/sortsupport.h"
#include "common/shortest_dec.h"

/* ----------
* Uncomment the following to enable compilation of dump_numeric()
Expand Down Expand Up @@ -4535,7 +4536,15 @@ float4_numeric(PG_FUNCTION_ARGS)
PG_RETURN_NUMERIC(make_result(&const_pinf));
}

snprintf(buf, sizeof(buf), "%.*g", FLT_DIG, val);
/*
* REAL datatype can store upto 4B of floating point data;
* anything larger than that gets truncated unless
* buf has extra places to store those extra_float_digits
*/
if (sql_dialect == SQL_DIALECT_TSQL && extra_float_digits > 0)
float_to_shortest_decimal_buf(val, buf);
else
snprintf(buf, sizeof(buf), "%.*g", FLT_DIG, val);

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similar logic can be found in float4out(); however in float4_numeric() the same was missing.

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we need more test cases to validate that this right check. This change implies that when dialect is TSQL, always try to use extra digits for REAL datatype when casting from float4 to numeric. Is it really the case for all possible casting scenario from float4 to numeric?

init_var(&result);

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