Here’s an example to demonstrate the difference. The trunc() function on the other hand simply truncates the number toward zero or to the specified decimal place. The number is rounded to the nearest integer or to the specified number of decimal places (depending on whether you give it one argument or two arguments). In some cases, the round() function might appear to work in a similar way to trunc(). Result: round | round | round | round | roundĨ00 | 790 | 500 | 490 | 0 Round() vs Trunc() Here’s what happens when the second argument is a negative value. Here’s an example of specifying a number of decimal places when the original number doesn’t include any fractional seconds. In this case it simply adds a zero to the right part of the fractional seconds. There’s nothing to stop you specifying more fractional seconds than is in the original number. In this case nothing was rounded, because I specified the exact number of decimal places that I provided. Here’s the same example again, but with two decimal places specified. However, it’s important to note that the result is completely dependent on how many fractional seconds you specify in the second argument. However, if we adjust the fractional seconds slightly, we’ll see that the result is rounded. In such cases, it returns the same result that we would have seen if we’d used the trunc() function. In this case, nothing was rounded up and zero was simply dropped. Here’s an example that uses the second syntax. If the fractional seconds were less than 50, it would have been rounded down, and the result would be 13. Many of these functions are provided in multiple forms with different argument types. UNSIGNED, if specified, disallows negative values. You must cast the value to be rounded to numeric to use the two-argument form of round. You can see that PostgreSQL is expanding it in the output). In this case the fractional seconds are 50 and so the number is rounded up to the nearest integer. In the table, dp indicates double precision. A double-precision floating-point number is accurate to approximately 15 decimal places. (In the above, note that float8 is just a shorthand alias for double precision. Here’s an example that uses the first syntax. The return type for this function is the same as the input type. In this case, v is the number, and s is the number of decimal places. The second syntax rounds it to a specified number of decimal places. The first syntax rounds the number to the nearest integer. The round() function can be used in either of the following ways: round(dp or numeric) This is determined by the number of arguments you pass to the function when you call it. For numeric values, ties are broken by rounding away from zero. Integer rounding round ( numeric) numeric round ( double precision) double precision. You can make it round the number to the nearest integer, or to a specified number of decimal places. round() has two variants, one which rounds to the nearest integer, the other which rounds to a specified number of decimal places. The function can work in one of two ways, depending on how you use it. Postgres=# select round(1230.In PostgreSQL, the round() function is used for rounding a number. Postgres-# ,round(cast(1235.5 as numeric)) as round_numeric_odd_5 Postgres-# ,round(cast(1234.5 as numeric)) as round_numeric_even_4 Postgres-# ,round(cast(1233.5 as numeric)) as round_numeric_odd_3 Postgres-# ,round(cast(1232.5 as numeric)) as round_numeric_even_2 Postgres-# ,round(cast(1231.5 as numeric)) as round_numeric_odd_1 Postgres=# select round(cast(1230.5 as numeric)) as round_numeric_even_0 Postgres-# ,round(cast(1235.5 as double precision)) as round_double_odd_5 For double precision the rounding probably depends on your platform. Postgres-# ,round(cast(1234.5 as double precision)) as round_double_even_4 If this would be documented then users can rely on its rounding behavior. The Frenchman tried to round Alisson but was unable to do so, prompting him to pass the ball to Federico Valverde. Postgres-# ,round(cast(1233.5 as double precision)) as round_double_odd_3 Postgres-# ,round(cast(1232.5 as double precision)) as round_double_even_2 Postgres-# ,round(cast(1231.5 as double precision)) as round_double_odd_1 Postgres=# select round(cast(1230.5 as double precision)) as round_double_even_0 (I haven't tested other versions, yet.) For double precision values, even whole numbers are rounded down, yet for odds they are rounded up. 5 rounding is handled differently between the types. Is the round() function implemented differently for double precision than for numeric? Forgive me if this exists somewhere in the documentation, but I can't seem to find it. I have a colleague of mine that keeps telling me not to use a double precision type for a PostgreSQL column, because I will eventually have rounding issues.
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