# String Distance Functions

Introduced in release: 1.14.

Drill provides a functions for calculating a variety well known string distance metrics. Typically, you use string distance functions in the WHERE clause of a query to measure the difference between two strings. For example, if you want to match a street address, but do not know how to spell a street name, you could execute a query on the data source with the street addresses:

``````   SELECT street_address
WHERE cosine_distance( `street_address`, “1234 North Quail Ln” ) <  0.5;
``````

The search would return addresses from rows with street addresses similar to 1234 North Quail Ln, such as:

``````   1234 N. Quail Lane
1234 N Quaile Lan
``````

Drill supports the following string distance functions.

Function Return type Description
COSINE_DISTANCE(string1, string2) FLOAT8 Returns the cosine distance, a measurement of the angular distance between between two strings regarded as word vectors.
FUZZY_SCORE(string1, string2) FLOAT8 Returns the score from a fuzzy string matching algorithm1. Higher scores indicate greater similarity.
HAMMING_DISTANCE(string1, string2) FLOAT8 Returns the Hamming distance between two strings of equal length, a measurement of the number of positions at which corresponding characters differ.
JACCARD_DISTANCE(string1, string2) FLOAT8 Returns the Jaccard distance between two strings regarded as unordered sets of characters, a measurement of the overlap between two sets.
JARO_DISTANCE(string1, string2) FLOAT8 Returns the Jaro-Winkler distance, a measurement of the fraction of matching characters between two strings.
LEVENSHTEIN_DISTANCE(string1, string2) FLOAT8 Returns the Levenshtein distance between two strings, a measurement of the number of single character modifications needed change one string into another.
LONGEST_COMMON_SUBSTRING_DISTANCE(string1, string2) FLOAT8 Returns the length of the longest common substring across two strings2.
1. Calculates the score from a matching algorithm similar to the searching algorithms implemented in editors such as Sublime Text, TextMate, Atom, and others. One point is given for every matched character. Subsequent matches yield two bonus points.

2. Generally this algorithm is fairly inefficient, as for length m, n of the input CharSequence’s left and right respectively, the runtime of the algorithm is O(m*n).