SQL 基础正则表达式（二十三）

Posted 2020-09-06

在SQL 和 PL/SQL 中使用正则表达式

函数名称	描述
REGEXP_LIKE	与LIKE运算符类似，但执行正则表达式匹配，而不是简单的模糊匹配（条件）
REGEXP_REPLACE	以正则表达式搜索和替换字符串
REGEXP_INSTR	以正则表达式搜索字符串，并返回匹配的位置
REGEXP_SUBSTR	以正则表达式搜索和提取匹配字符串
REGEXP_COUNT	返回匹配的次数

什么是元字符？

元字符是特殊字符有特殊的含义，如一个通配符，重复字符，一个不匹配的字符，一个范围内的符。

您可以使用多个预定义的元字符符号的模式匹配。

例如, ^(f|ht)tps?:$ 正则表达式搜索字符串从以下开始：

– 字面值 f 或 ht

– 字面值 t

– 字面值 p,字面值s 可选

– 冒号“:” 结尾的字面值

正则表达式的元字符

语法	描述
.	Matches any character in the supported character set, except NULL
+	Matches one or more occurrences
?	Matches zero or one occurrence
*	Matches zero or more occurrences of the preceding subexpression
{m}	Matches exactly m occurrences of the preceding expression
{m, }	Matches at least m occurrences of the preceding subexpression
{m,n}	Matches at least m, but not more than n, occurrences of the preceding subexpression
[…]	Matches any single character in the list within the brackets
|	Matches one of the alternatives
( ... )	Treats the enclosed expression within the parentheses as a unit. The subexpression can be a string of literals or a complex expression containing operators.
^	Matches the beginning of a string
$	Matches the end of a string
\	Treats the subsequent metacharacter in the expression as a literal
\n	Matches the nth (1–9) preceding subexpression of whatever is grouped within parentheses. The parentheses cause an expression to be remembered; a backreference refers to it.
\d	A digit character
[:class:]	Matches any character belonging to the specified POSIX character class
[^:class:]	Matches any single character not in the list within the brackets

REGEXP_LIKE (source_char, pattern [,match_option]

REGEXP_INSTR (source_char, pattern [, position

[, occurrence [, return_option

[, match_option [, subexpr]]]]])

REGEXP_SUBSTR (source_char, pattern [, position

[, occurrence [, match_option

[, subexpr]]]])

REGEXP_REPLACE(source_char, pattern [,replacestr

[, position [, occurrence

[, match_option]]]])

REGEXP_COUNT (source_char, pattern [, position

[, occurrence [, match_option]]])

使用REGEXP_LIKE 执行基本搜索

REGEXP_LIKE(source_char, pattern [, match_parameter ])

SELECT first_name, last_name FROM employees

WHERE REGEXP_LIKE (first_name, ‘^Ste(v|ph)en$‘);

使用REGEXP_REPLACE 替换

REGEXP_REPLACE(source_char, pattern [,replacestr

[, position [, occurrence [, match_option]]]])

SELECT REGEXP_REPLACE(phone_number, ‘\.‘,‘-‘) AS phone

FROM employees;

使用 REGEXP_INSTR 插入

REGEXP_INSTR (source_char, pattern [, position [,

occurrence [, return_option [, match_option]]]])

SELECT street_address,REGEXP_INSTR(street_address,‘[[:alpha:]]‘) AS

First_Alpha_Position

FROM locations;

使用 REGEXP_SUBSTR 函数提取字符串

REGEXP_SUBSTR (source_char, pattern [, position [, occurrence [, match_option]]])

SELECT REGEXP_SUBSTR(street_address , ‘ [^ ]+ ‘) AS Road FROM locations;

子表达式

使用子表达式与正则表达式支持

SELECT

REGEXP_INSTR

(‘0123456789‘, -- source char or search value

‘(123)(4(56)(78))‘, -- regular expression patterns

1, -- position to start searching

1, -- occurrence

0, -- return option

‘i‘, -- match option (case insensitive)

1) -- sub-expression on which to search

"Position"

FROM dual;

为什么要访问第n个子表达式

一个更实际的用途：DNA测序

您可能需要找到一个特定的子模式，确定了在小鼠DNA免疫

所需的蛋白质。

SELECT REGEXP_INSTR(‘ ccacctttccctccactcctcacgttctcacctgtaaagcgtccctc

cctcatccccatgcccccttaccctgcagggtagagtaggctagaaaccagagagctccaagc

tccatctgtggagaggtgccatccttgggctgcagagagaggagaatttgccccaaagctgcc

tgcagagcttcaccacccttagtctcacaaagccttgagttcatagcatttcttgagttttca

ccctgcccagcaggacactgcagcacccaaagggcttcccaggagtagggttgccctcaagag

gctcttgggtctgatggccacatcctggaattgttttcaagttgatggtcacagccctgaggc

atgtaggggcgtggggatgcgctctgctctgctctcctctcctgaacccctgaaccctctggc

taccccagagcacttagagccag ‘,

‘(gtc(tcac)(aaag))‘,

1, 1, 0, ‘i‘,

1) "Position"

FROM dual;

REGEXP_SUBSTR 示例

SELECT

REGEXP_SUBSTR

(‘acgctgcactgca‘, -- source char or search value

‘acg(.*)gca‘, -- regular expression pattern

1, -- position to start searching

1, -- occurrence

‘i‘, -- match option (case insensitive)

1) -- sub-expression

"Value"

FROM dual;

使用 REGEXP_COUNT函数

REGEXP_COUNT (source_char, pattern [, position

[, occurrence [, match_option]]])

SELECT REGEXP_COUNT(

‘ccacctttccctccactcctcacgttctcacctgtaaagcgtccctccctcatccccatgcccccttaccctgcag

ggtagagtaggctagaaaccagagagctccaagctccatctgtggagaggtgccatccttgggctgcagagagaggag

aatttgccccaaagctgcctgcagagcttcaccacccttagtctcacaaagccttgagttcatagcatttcttgagtt

ttcaccctgcccagcaggacactgcagcacccaaagggcttcccaggagtagggttgccctcaagaggctcttgggtc

tgatggccacatcctggaattgttttcaagttgatggtcacagccctgaggcatgtaggggcgtggggatgcgctctg

ctctgctctcctctcctgaacccctgaaccctctggctaccccagagcacttagagccag‘ ,

‘gtc‘) AS Count

FROM dual;

Check约束和正则表达式：示例

ALTER TABLE emp8

ADD CONSTRAINT email_addr

CHECK(REGEXP_LIKE(email,‘@‘)) NOVALIDATE;

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