mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-14 19:45:11 +00:00
d91c97d15d
* Replace underscores with hyphens * remove temporary code * fix style check * fix collapse
483 lines
15 KiB
Markdown
483 lines
15 KiB
Markdown
---
|
||
toc_priority: 50
|
||
toc_title: Hash
|
||
---
|
||
|
||
# Hash Functions {#hash-functions}
|
||
|
||
Hash functions can be used for the deterministic pseudo-random shuffling of elements.
|
||
|
||
## halfMD5 {#hash-functions-halfmd5}
|
||
|
||
[Interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_functions-reinterpretAsString) all the input parameters as strings and calculates the [MD5](https://en.wikipedia.org/wiki/MD5) hash value for each of them. Then combines hashes, takes the first 8 bytes of the hash of the resulting string, and interprets them as `UInt64` in big-endian byte order.
|
||
|
||
``` sql
|
||
halfMD5(par1, ...)
|
||
```
|
||
|
||
The function is relatively slow (5 million short strings per second per processor core).
|
||
Consider using the [sipHash64](#hash_functions-siphash64) function instead.
|
||
|
||
**Parameters**
|
||
|
||
The function takes a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
A [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT halfMD5(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS halfMD5hash, toTypeName(halfMD5hash) AS type
|
||
```
|
||
|
||
``` text
|
||
┌────────halfMD5hash─┬─type───┐
|
||
│ 186182704141653334 │ UInt64 │
|
||
└────────────────────┴────────┘
|
||
```
|
||
|
||
## MD5 {#hash_functions-md5}
|
||
|
||
Calculates the MD5 from a string and returns the resulting set of bytes as FixedString(16).
|
||
If you don’t need MD5 in particular, but you need a decent cryptographic 128-bit hash, use the ‘sipHash128’ function instead.
|
||
If you want to get the same result as output by the md5sum utility, use lower(hex(MD5(s))).
|
||
|
||
## sipHash64 {#hash_functions-siphash64}
|
||
|
||
Produces a 64-bit [SipHash](https://131002.net/siphash/) hash value.
|
||
|
||
``` sql
|
||
sipHash64(par1,...)
|
||
```
|
||
|
||
This is a cryptographic hash function. It works at least three times faster than the [MD5](#hash_functions-md5) function.
|
||
|
||
Function [interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_functions-reinterpretAsString) all the input parameters as strings and calculates the hash value for each of them. Then combines hashes by the following algorithm:
|
||
|
||
1. After hashing all the input parameters, the function gets the array of hashes.
|
||
2. Function takes the first and the second elements and calculates a hash for the array of them.
|
||
3. Then the function takes the hash value, calculated at the previous step, and the third element of the initial hash array, and calculates a hash for the array of them.
|
||
4. The previous step is repeated for all the remaining elements of the initial hash array.
|
||
|
||
**Parameters**
|
||
|
||
The function takes a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
A [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT sipHash64(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS SipHash, toTypeName(SipHash) AS type
|
||
```
|
||
|
||
``` text
|
||
┌──────────────SipHash─┬─type───┐
|
||
│ 13726873534472839665 │ UInt64 │
|
||
└──────────────────────┴────────┘
|
||
```
|
||
|
||
## sipHash128 {#hash_functions-siphash128}
|
||
|
||
Calculates SipHash from a string.
|
||
Accepts a String-type argument. Returns FixedString(16).
|
||
Differs from sipHash64 in that the final xor-folding state is only done up to 128 bits.
|
||
|
||
## cityHash64 {#cityhash64}
|
||
|
||
Produces a 64-bit [CityHash](https://github.com/google/cityhash) hash value.
|
||
|
||
``` sql
|
||
cityHash64(par1,...)
|
||
```
|
||
|
||
This is a fast non-cryptographic hash function. It uses the CityHash algorithm for string parameters and implementation-specific fast non-cryptographic hash function for parameters with other data types. The function uses the CityHash combinator to get the final results.
|
||
|
||
**Parameters**
|
||
|
||
The function takes a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
A [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Examples**
|
||
|
||
Call example:
|
||
|
||
``` sql
|
||
SELECT cityHash64(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS CityHash, toTypeName(CityHash) AS type
|
||
```
|
||
|
||
``` text
|
||
┌─────────────CityHash─┬─type───┐
|
||
│ 12072650598913549138 │ UInt64 │
|
||
└──────────────────────┴────────┘
|
||
```
|
||
|
||
The following example shows how to compute the checksum of the entire table with accuracy up to the row order:
|
||
|
||
``` sql
|
||
SELECT groupBitXor(cityHash64(*)) FROM table
|
||
```
|
||
|
||
## intHash32 {#inthash32}
|
||
|
||
Calculates a 32-bit hash code from any type of integer.
|
||
This is a relatively fast non-cryptographic hash function of average quality for numbers.
|
||
|
||
## intHash64 {#inthash64}
|
||
|
||
Calculates a 64-bit hash code from any type of integer.
|
||
It works faster than intHash32. Average quality.
|
||
|
||
## SHA1 {#sha1}
|
||
|
||
## SHA224 {#sha224}
|
||
|
||
## SHA256 {#sha256}
|
||
|
||
Calculates SHA-1, SHA-224, or SHA-256 from a string and returns the resulting set of bytes as FixedString(20), FixedString(28), or FixedString(32).
|
||
The function works fairly slowly (SHA-1 processes about 5 million short strings per second per processor core, while SHA-224 and SHA-256 process about 2.2 million).
|
||
We recommend using this function only in cases when you need a specific hash function and you can’t select it.
|
||
Even in these cases, we recommend applying the function offline and pre-calculating values when inserting them into the table, instead of applying it in SELECTS.
|
||
|
||
## URLHash(url\[, N\]) {#urlhashurl-n}
|
||
|
||
A fast, decent-quality non-cryptographic hash function for a string obtained from a URL using some type of normalization.
|
||
`URLHash(s)` – Calculates a hash from a string without one of the trailing symbols `/`,`?` or `#` at the end, if present.
|
||
`URLHash(s, N)` – Calculates a hash from a string up to the N level in the URL hierarchy, without one of the trailing symbols `/`,`?` or `#` at the end, if present.
|
||
Levels are the same as in URLHierarchy. This function is specific to Yandex.Metrica.
|
||
|
||
## farmHash64 {#farmhash64}
|
||
|
||
Produces a 64-bit [FarmHash](https://github.com/google/farmhash) hash value.
|
||
|
||
``` sql
|
||
farmHash64(par1, ...)
|
||
```
|
||
|
||
The function uses the `Hash64` method from all [available methods](https://github.com/google/farmhash/blob/master/src/farmhash.h).
|
||
|
||
**Parameters**
|
||
|
||
The function takes a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
A [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT farmHash64(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS FarmHash, toTypeName(FarmHash) AS type
|
||
```
|
||
|
||
``` text
|
||
┌─────────────FarmHash─┬─type───┐
|
||
│ 17790458267262532859 │ UInt64 │
|
||
└──────────────────────┴────────┘
|
||
```
|
||
|
||
## javaHash {#hash_functions-javahash}
|
||
|
||
Calculates [JavaHash](http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/478a4add975b/src/share/classes/java/lang/String.java#l1452) from a string. This hash function is neither fast nor having a good quality. The only reason to use it is when this algorithm is already used in another system and you have to calculate exactly the same result.
|
||
|
||
**Syntax**
|
||
|
||
``` sql
|
||
SELECT javaHash('');
|
||
```
|
||
|
||
**Returned value**
|
||
|
||
A `Int32` data type hash value.
|
||
|
||
**Example**
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT javaHash('Hello, world!');
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─javaHash('Hello, world!')─┐
|
||
│ -1880044555 │
|
||
└───────────────────────────┘
|
||
```
|
||
|
||
## javaHashUTF16LE {#javahashutf16le}
|
||
|
||
Calculates [JavaHash](http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/478a4add975b/src/share/classes/java/lang/String.java#l1452) from a string, assuming it contains bytes representing a string in UTF-16LE encoding.
|
||
|
||
**Syntax**
|
||
|
||
``` sql
|
||
javaHashUTF16LE(stringUtf16le)
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
- `stringUtf16le` — a string in UTF-16LE encoding.
|
||
|
||
**Returned value**
|
||
|
||
A `Int32` data type hash value.
|
||
|
||
**Example**
|
||
|
||
Correct query with UTF-16LE encoded string.
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT javaHashUTF16LE(convertCharset('test', 'utf-8', 'utf-16le'))
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─javaHashUTF16LE(convertCharset('test', 'utf-8', 'utf-16le'))─┐
|
||
│ 3556498 │
|
||
└──────────────────────────────────────────────────────────────┘
|
||
```
|
||
|
||
## hiveHash {#hash-functions-hivehash}
|
||
|
||
Calculates `HiveHash` from a string.
|
||
|
||
``` sql
|
||
SELECT hiveHash('');
|
||
```
|
||
|
||
This is just [JavaHash](#hash_functions-javahash) with zeroed out sign bit. This function is used in [Apache Hive](https://en.wikipedia.org/wiki/Apache_Hive) for versions before 3.0. This hash function is neither fast nor having a good quality. The only reason to use it is when this algorithm is already used in another system and you have to calculate exactly the same result.
|
||
|
||
**Returned value**
|
||
|
||
A `Int32` data type hash value.
|
||
|
||
Type: `hiveHash`.
|
||
|
||
**Example**
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT hiveHash('Hello, world!');
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─hiveHash('Hello, world!')─┐
|
||
│ 267439093 │
|
||
└───────────────────────────┘
|
||
```
|
||
|
||
## metroHash64 {#metrohash64}
|
||
|
||
Produces a 64-bit [MetroHash](http://www.jandrewrogers.com/2015/05/27/metrohash/) hash value.
|
||
|
||
``` sql
|
||
metroHash64(par1, ...)
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
The function takes a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
A [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT metroHash64(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS MetroHash, toTypeName(MetroHash) AS type
|
||
```
|
||
|
||
``` text
|
||
┌────────────MetroHash─┬─type───┐
|
||
│ 14235658766382344533 │ UInt64 │
|
||
└──────────────────────┴────────┘
|
||
```
|
||
|
||
## jumpConsistentHash {#jumpconsistenthash}
|
||
|
||
Calculates JumpConsistentHash form a UInt64.
|
||
Accepts two arguments: a UInt64-type key and the number of buckets. Returns Int32.
|
||
For more information, see the link: [JumpConsistentHash](https://arxiv.org/pdf/1406.2294.pdf)
|
||
|
||
## murmurHash2\_32, murmurHash2\_64 {#murmurhash2-32-murmurhash2-64}
|
||
|
||
Produces a [MurmurHash2](https://github.com/aappleby/smhasher) hash value.
|
||
|
||
``` sql
|
||
murmurHash2_32(par1, ...)
|
||
murmurHash2_64(par1, ...)
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
Both functions take a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
- The `murmurHash2_32` function returns hash value having the [UInt32](../../sql-reference/data-types/int-uint.md) data type.
|
||
- The `murmurHash2_64` function returns hash value having the [UInt64](../../sql-reference/data-types/int-uint.md) data type.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT murmurHash2_64(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS MurmurHash2, toTypeName(MurmurHash2) AS type
|
||
```
|
||
|
||
``` text
|
||
┌──────────MurmurHash2─┬─type───┐
|
||
│ 11832096901709403633 │ UInt64 │
|
||
└──────────────────────┴────────┘
|
||
```
|
||
|
||
## gccMurmurHash {#gccmurmurhash}
|
||
|
||
Calculates a 64-bit [MurmurHash2](https://github.com/aappleby/smhasher) hash value using the same hash seed as [gcc](https://github.com/gcc-mirror/gcc/blob/41d6b10e96a1de98e90a7c0378437c3255814b16/libstdc%2B%2B-v3/include/bits/functional_hash.h#L191). It is portable between CLang and GCC builds.
|
||
|
||
**Syntax**
|
||
|
||
``` sql
|
||
gccMurmurHash(par1, ...);
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
- `par1, ...` — A variable number of parameters that can be any of the [supported data types](../../sql-reference/data-types/index.md#data_types).
|
||
|
||
**Returned value**
|
||
|
||
- Calculated hash value.
|
||
|
||
Type: [UInt64](../../sql-reference/data-types/int-uint.md).
|
||
|
||
**Example**
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT
|
||
gccMurmurHash(1, 2, 3) AS res1,
|
||
gccMurmurHash(('a', [1, 2, 3], 4, (4, ['foo', 'bar'], 1, (1, 2)))) AS res2
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─────────────────res1─┬────────────────res2─┐
|
||
│ 12384823029245979431 │ 1188926775431157506 │
|
||
└──────────────────────┴─────────────────────┘
|
||
```
|
||
|
||
## murmurHash3\_32, murmurHash3\_64 {#murmurhash3-32-murmurhash3-64}
|
||
|
||
Produces a [MurmurHash3](https://github.com/aappleby/smhasher) hash value.
|
||
|
||
``` sql
|
||
murmurHash3_32(par1, ...)
|
||
murmurHash3_64(par1, ...)
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
Both functions take a variable number of input parameters. Parameters can be any of the [supported data types](../../sql-reference/data-types/index.md).
|
||
|
||
**Returned Value**
|
||
|
||
- The `murmurHash3_32` function returns a [UInt32](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
- The `murmurHash3_64` function returns a [UInt64](../../sql-reference/data-types/int-uint.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT murmurHash3_32(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:00:00')) AS MurmurHash3, toTypeName(MurmurHash3) AS type
|
||
```
|
||
|
||
``` text
|
||
┌─MurmurHash3─┬─type───┐
|
||
│ 2152717 │ UInt32 │
|
||
└─────────────┴────────┘
|
||
```
|
||
|
||
## murmurHash3\_128 {#murmurhash3-128}
|
||
|
||
Produces a 128-bit [MurmurHash3](https://github.com/aappleby/smhasher) hash value.
|
||
|
||
``` sql
|
||
murmurHash3_128( expr )
|
||
```
|
||
|
||
**Parameters**
|
||
|
||
- `expr` — [Expressions](../syntax.md#syntax-expressions) returning a [String](../../sql-reference/data-types/string.md)-type value.
|
||
|
||
**Returned Value**
|
||
|
||
A [FixedString(16)](../../sql-reference/data-types/fixedstring.md) data type hash value.
|
||
|
||
**Example**
|
||
|
||
``` sql
|
||
SELECT murmurHash3_128('example_string') AS MurmurHash3, toTypeName(MurmurHash3) AS type
|
||
```
|
||
|
||
``` text
|
||
┌─MurmurHash3──────┬─type────────────┐
|
||
│ 6<>1 <1C>4"S5KT<4B>~~q │ FixedString(16) │
|
||
└──────────────────┴─────────────────┘
|
||
```
|
||
|
||
## xxHash32, xxHash64 {#hash-functions-xxhash32}
|
||
|
||
Calculates `xxHash` from a string. It is proposed in two flavors, 32 and 64 bits.
|
||
|
||
``` sql
|
||
SELECT xxHash32('');
|
||
|
||
OR
|
||
|
||
SELECT xxHash64('');
|
||
```
|
||
|
||
**Returned value**
|
||
|
||
A `Uint32` or `Uint64` data type hash value.
|
||
|
||
Type: `xxHash`.
|
||
|
||
**Example**
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT xxHash32('Hello, world!');
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─xxHash32('Hello, world!')─┐
|
||
│ 834093149 │
|
||
└───────────────────────────┘
|
||
```
|
||
|
||
**See Also**
|
||
|
||
- [xxHash](http://cyan4973.github.io/xxHash/).
|
||
|
||
[Original article](https://clickhouse.tech/docs/en/query_language/functions/hash_functions/) <!--hide-->
|