PostgreSQL 14 preview - bit_count 计算比特位1的个数

作者

digoal

日期

2021-03-24

标签

PostgreSQL , bit_count

背景

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=a6715af1e72da289474011be1e2d536f991eda34

+/* + * bit_count + * + * Returns the number of bits set in a bit string. + */ +Datum +bit_bit_count(PG_FUNCTION_ARGS) +{ + VarBit *arg = PG_GETARG_VARBIT_P(0); + + PG_RETURN_INT64(pg_popcount((char *) VARBITS(arg), VARBITBYTES(arg))); +} +

```
Add bit_count SQL function
author Peter Eisentraut peter@eisentraut.org
Tue, 23 Mar 2021 07:45:51 +0000 (08:45 +0100)
committer Peter Eisentraut peter@eisentraut.org
Tue, 23 Mar 2021 09:13:58 +0000 (10:13 +0100)
commit a6715af1e72da289474011be1e2d536f991eda34
tree 48ae8ef2c5c858baf43611b8a65c4ec22cbe47bf tree
parent 5aed6a1fc214913de9ac69c1717dc64a2483e16d commit | diff
Add bit_count SQL function

This function for bit and bytea counts the set bits in the bit or byte
string. Internally, we use the existing popcount functionality.

For the name, after some discussion, we settled on bit_count, which
also exists with this meaning in MySQL, Java, and Python.

Author: David Fetter david@fetter.org
Discussion: https://www.postgresql.org/message-id/flat/20201230105535.GJ13234@fetter.org
```

```
+-- bit_count
+SELECT bit_count(B'0101011100'::bit(10));
+ bit_count
+-----------
+ 5
+(1 row)
+
+SELECT bit_count(B'1111111111'::bit(10));
+ bit_count
+-----------
+ 10
+(1 row)

+SELECT bit_count('\x1234567890'::bytea);
+ bit_count
+-----------
+ 31
+(1 row)
```

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