String functions

CONCAT()

Concatenates two or more strings into one. Non-string arguments must be explicitly converted to string using TO_STRING() function

  1. CONCAT(TO_STRING(float_attr), ',', TO_STRING(int_attr), ',', title)

LEVENSHTEIN()

LEVENSHTEIN ( pattern, source, {normalize=0, length_delta=0}) returns number (Levenshtein distance) of single-character edits (insertions, deletions or substitutions) between pattern and source strings required to make in pattern to make it source.

  • pattern, source - constant string, string field name, JSON field name or any expression which produces a string (like e.g. SUBSTRING_INDEX()))
  • normalize - option to get distance as a float number in the range of [0.0 - 1.0], where 0.0 is the exact match and 1.0 is the maximum difference. Default value is 0, means to not normalize and provide the result as integer.
  • length_delta - to skip Levenshtein distance calculation and return max(strlen(pattern), strlen(source)) in case the option is set and lengths of the strings differ more than by length_delta value. Default value is 0, means to calculate Levenshtein distance for any input strings. This option could be useful in case of checking mostly similar strings.
  1. SELECT LEVENSHTEIN('gily', attr1) AS dist, WEIGHT() AS w FROM test WHERE MATCH('test') ORDER BY w DESC, dist ASC;
  2. SELECT LEVENSHTEIN('gily', j.name, {length_delta=6}) AS dist, WEIGHT() AS w FROM test WHERE MATCH('test') ORDER BY w DESC;
  3. SELECT LEVENSHTEIN(title, j.name, {normalize=1}) AS dist, WEIGHT() AS w FROM test WHERE MATCH ('test') ORDER BY w DESC, dist ASC;

REGEX()

REGEX(attr,expr) function returns 1 if regular expression matched to string of attribute and 0 otherwise. It works with both string and JSON attributes.

  1. SELECT REGEX(content, 'box?') FROM test;
  2. SELECT REGEX(j.color, 'red | pink') FROM test;

The expression should follow the RE2 syntax. For example, for case insensitive search you can do:

  1. SELECT REGEX(content, '(?i)box') FROM test;

SNIPPET()

SNIPPET() can be used to highlight search results in a given text. The first two arguments are: the text to highlight, and a query. It’s possible to pass options to the function as the third, fourth and so on arguments. SNIPPET() can fetch the text to use in highlighting from the table itself. The first argument in this case should be field name:

  1. SELECT SNIPPET(body, QUERY()) FROM myIndex WHERE MATCH('my.query')

QUERY() expression in this example returns current fulltext query. SNIPPET() can also highlight non-indexed text:

  1. mysql  SELECT id, SNIPPET('text to highlight', 'my.query', 'limit=100') FROM myIndex WHERE MATCH('my.query')

It can also be used to highlight the text fetched from other sources using an UDF:

  1. SELECT id, SNIPPET(myUdf(id), 'my.query', 'limit=100') FROM myIndex WHERE MATCH('my.query')

where myUdf() would be a UDF that fetches a document by its ID from some external storage. SNIPPET() is a “post limit” function, meaning that computing snippets is postponed not just until the entire final result set is ready, but even after the LIMIT clause is applied. For example, with a LIMIT 20,10 clause, SNIPPET() will be called at most 10 times.

Note, SNIPPET() doesn’t support limiting by fields. Use HIGHLIGHT() instead.

SUBSTRING_INDEX()

SUBSTRING_INDEX(string, delimiter, number) returns a substring of a string before a specified number of delimiter occurs

  • string - The original string. Can be a constant string or a string from a string/json attribute.
  • delimiter - The delimiter to search for
  • number - The number of times to search for the delimiter. Can be both a positive or negative number.If it is a positive number, this function will return all to the left of the delimiter. If it is a negative number, this function will return all to the right of the delimiter.
  1. SELECT SUBSTRING_INDEX('www.w3schools.com', '.', 2) FROM test;
  2. SELECT SUBSTRING_INDEX(j.coord, ' ', 1) FROM test;

Other functions

LAST_INSERT_ID()

Returns ids of documents inserted or replaced by last statement in the current session.

The same value can be also received via @@session.last_insert_id variable:

  1. mysql> select @@session.last_insert_id;
  2. +--------------------------+
  3. | @@session.last_insert_id |
  4. +--------------------------+
  5. | 11,32                    |
  6. +--------------------------+
  7. 1 rows in set
  9. mysql> select LAST_INSERT_ID();
  10. +------------------+
  11. | LAST_INSERT_ID() |
  12. +------------------+
  13. | 25,26,29         |
  14. +------------------+
  15. 1 rows in set

SELECT @@system_variable

  1. SELECT @@system_variable [LIMIT [offset,] row_count]

This is currently a placeholder query that does nothing and reports success. That is in order to keep compatibility with frameworks and connectors that automatically execute this statement.

However @@session.last_insert_id and LAST_INSERT_ID() report ID of documents these were inserted or replaced well at last statement.

  1. mysql> select @@session.last_insert_id;
  2. +--------------------------+
  3. | @@session.last_insert_id |
  4. +--------------------------+
  5. | 11,32                    |
  6. +--------------------------+
  7. 1 rows in set
  9. mysql> select LAST_INSERT_ID();
  10. +------------------+
  11. | LAST_INSERT_ID() |
  12. +------------------+
  13. | 25,26,29         |
  14. +------------------+
  15. 1 rows in set

CONNECTION_ID()

Returns current connection id.

  1. mysql> select CONNECTION_ID();
  2. +-----------------+
  3. | CONNECTION_ID() |
  4. +-----------------+
  5. | 6               |
  6. +-----------------+
  7. 1 row in set (0.00 sec)

▪️ Securing and compacting a table