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PostgreSQL LIKE语句

PostgreSQL的LIKE操作符是用来反对使用通配符的模式匹配的文本值。如果搜索表达式可以匹配的模式表达式,LIKE运算将返回true,也就是1。

有两个通配符与LIKE运算符一起使用:

  • 百分号 (%)

  • 下划线 (_)

百分号表示零个,一个或多个数字或字符。下划线代表一个单一的数字或字符。这些符号可以被组合使用。

那么,如果这两个标志结合LIKE子句中不使用LIKE的行为就象等于运算符。

语法:

%和_的基本语法如下:

SELECT FROM table_name
WHERE column LIKE 'XXXX%'

or

SELECT FROM table_name
WHERE column LIKE '%XXXX%'

or

SELECT FROM table_name
WHERE column LIKE 'XXXX_'

or

SELECT FROM table_name
WHERE column LIKE '_XXXX'

or

SELECT FROM table_name
WHERE column LIKE '_XXXX_'

可以结合使用AND或OR运算的N多的条件。XXXX在这里可以是任何数字或字符串值。

实例:

下面一些例子显示LIKE子句以'%'和'_'运算符具有不同的部分:

Statement Description
WHERE SALARY::text LIKE '200%' Finds any values that start with 200
WHERE SALARY::text LIKE '%200%' Finds any values that have 200 in any position
WHERE SALARY::text LIKE '_00%' Finds any values that have 00 in the second and third positions
WHERE SALARY::text LIKE '2_%_%' Finds any values that start with 2 and are at least 3 characters in length
WHERE SALARY::text LIKE '%2' Finds any values that end with 2
WHERE SALARY::text LIKE '_2%3' Finds any values that have a 2 in the second position and end with a 3
WHERE SALARY::text LIKE '2___3' Finds any values in a five-digit number that start with 2 and end with 3
Postgres的LIKE只字符串比较。因此需要显式地将字符串作为整数列在上面的例子中。

让我们举一个现实的例子,考虑表公司有如下记录:

# select * from COMPANY;
 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Allen |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000
(7 rows)

以下是一个例子,它会从公司表显示年龄以2开始所有记录:

testdb=# SELECT * FROM COMPANY WHERE AGE::text LIKE '2%';

这将产生以下结果:

 id | name  | age | address     | salary
----+-------+-----+-------------+--------
  2 | Allen |  25 | Texas       |  15000
  3 | Teddy |  23 | Norway      |  20000
  4 | Mark  |  25 | Rich-Mond   |  65000
  5 | David |  27 | Texas       |  85000
  6 | Kim   |  22 | South-Hall  |  45000
  7 | James |  24 | Houston     |  10000
  8 | Paul  |  24 | Houston     |  20000
(7 rows)

以下是一个例子,它会显示所有记录从公司表的地址将有一个连字符( - ),里面的文字:

testdb=# SELECT * FROM COMPANY WHERE ADDRESS  LIKE '%-%';

这将产生以下结果:

 id | name | age |                      address              | salary
----+------+-----+-------------------------------------------+--------
  4 | Mark |  25 | Rich-Mond                                 |  65000
  6 | Kim  |  22 | South-Hall                                |  45000
(2 rows)