![]() ![]() Quick Example: - Find cities that start with A SELECT name FROM cities WHERE name REGEXP 'A' Overview: Synonyms REGEXP and RLIKE are synonyms Syntax string NOT REGEXP pattern Return 1 string matches pattern 0 string does. MariaDB 10.0.11 introduced the default_regex_flags variable to address the remaining compatibilities between PCRE and the old regex library. REGEXP and RLIKE operators check whether the string matches pattern containing a regular expression. | 'a' REGEXP 'A' | 'a' REGEXP BINARY 'A' | SELECT 'a' REGEXP 'A', 'a' REGEXP BINARY 'A' SELECT 'new*\n*line' REGEXP 'new\\*.\\*line' The default_regex_flags variable addresses the remaining compatibilities between PCRE and the old regex library. This tutorial explains pattern matching using the MySQL LIKE operator: Pattern matching is an important feature in almost all programming languages like Java/C/Python etc which mostly leverage the usage of Regular Expressions for pattern matching against a given string input. MariaDB 10.0.5 moved to the PCRE regex library - see PCRE Regular Expressions for enhancements to REGEXP introduced in MariaDB 10.0.5. REGEXP is not case sensitive, except when used with binary strings. Note: Because MariaDB uses the C escape syntax in strings (forĮxample, "\n" to represent the newline character), you must double any Specified as a string expression or table column. The pattern need not be a literal string. RLIKE and NOT RLIKE are synonyms for REGEXP and NOT REGEXP, originally provided for mSQL compatibility. The negative form NOT REGEXP also exists, as an alias for NOT (string REGEXP pattern). If you are aware of PHP or PERL, then it is very simple for you to understand because this matching is same like those scripting the regular expressions. If either expr or pat are NULL, the result is NULL. Returns 1 if expr matches pat or 0 if it doesn't match. Regular expressions (see also PCRE Regular Expressions). See Regular Expressions Overview for details on the syntax for The pattern can be an extended regular expression. select * from a FULL OUTER JOIN b on a.a = b.Performs a pattern match of a string expression expr against a pattern If something in A doesn't have a corresponding datum in B, then the B portion is null, and vice versa. Select a.*, b.* from a,b where a.a(+) = b.b Ī full outer join will give you the union of A and B, i.e. select * from a RIGHT OUTER JOIN b on a.a = b.b ![]() Select a.*, b.* from a,b where a.a = b.b(+) Ī right outer join will give all rows in B, plus any common rows in A. select * from a LEFT OUTER JOIN b on a.a = b.b Select a.*, b.* from a,b where a.a = b.b Ī left outer join will give all rows in A, plus any common rows in B. select * from a INNER JOIN b on a.a = b.b Note that (1,2) are unique to A, (3,4) are common, and (5,6) are unique to B.Īn inner join using either of the equivalent queries gives the intersection of the two tables, i.e. Suppose you have two tables, with a single column each, and data as follows: A B the inner part of a Venn diagram intersection.Īn outer join of A and B gives the results of A union B, i.e. The performance of like when using an index is very close to = (assuming the same number of rows returned).Īssuming you're joining on columns with no duplicates, which is a very common case:Īn inner join of A and B gives the result of A intersect B, i.e. SELECT * FROM t WHERE a LIKE '_agf' <<- cannot use an index SELECT * FROM t WHERE a LIKE '%a%' <<- cannot use an index ![]() SELECT * FROM t WHERE a LIKE 'a%' <<- can use an index, depending on cardinality Normally, if any expression in a string comparison is case-sensitive, the comparison is. A number converted to a string is treated as a binary string. If a string function is given a binary string as an argument, the resulting string is also a binary string. SELECT * FROM t WHERE a LIKE 'abc%' <<- can use an index Table 12.13 String Comparison Functions and Operators. SELECT * FROM t WHERE a LIKE 'abc' <<- (case insensitive `=`) can use an index In your case a firstname is more likely to be matched using LIKE than REGEXP and hence, it will be more optimized. LIKE is used to add wildcards to a string whereas REGEXP is used to match an attribute with Regular Expressions. REGEXPLIKE REGEXPINSTR REGEXPREPLACE REGEXPSUBSTR REGEXPLIKE simply takes a subject string, a pattern that gets compiled into a regular expression, and an optional parameter string, more on that later. LIKE can use an index if the wildcard is not the first char. REGEXP and LIKE are used to totally different cases. No other indexes on the same table are better suited (MySQL can only use one index per table per subselect) Ĭonsidering these and some other more esoteric caveats an = comparison is much faster than a regexp.the values in the column have sufficient cardinality (if more than +/- 20% of the rows match, MySQL will not use an index, because in that case doing a full table scan is faster).The regexp can never use an index in MySQL. ![]()
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