ClickHouse/docs/en/sql-reference/functions/hash-functions.md
2020-10-31 09:04:18 -04:00

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---
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 dont 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 cant 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.
## farmFingerprint64 {#farmfingerprint64}
## farmHash64 {#farmhash64}
Produces a 64-bit [FarmHash](https://github.com/google/farmhash) or Fingerprint value. Prefer `farmFingerprint64` for a stable and portable value.
``` sql
farmFingerprint64(par1, ...)
farmHash64(par1, ...)
```
These functions use the `Fingerprint64` and `Hash64` method respectively 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](../../sql-reference/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-->