python中的mysql数据库LIKE操作符详解

LIKE 操作符用于在 WHERE 子句中搜索列中的指定模式。

语法：

SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern

pattern这里就是放指定模板的地方，而这里就要用到“ % ”，也叫做通配符

%如果是放在条件前面，那就是查以...结尾的数据；例如：%李

%如果是放在条件后面，那就是查以...开头的数据；例如：李%

%如果是在条件前后都存在，那就是查包含的数据；例如：%李%

小知识点：

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '%z' at line 1

1064的错误就是LIKE查询时(语法错误)，通配符处没加引号，所以才会报错...

正确展示例如："%李%"

示例1：终端运行sql且WHERE子句中使用LIKE

查询地址以Hang开头的人员信息

root@7c6316b19d80:/# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 140
Server version: 5.6.51 MySQL Community Server (GPL)
 
mysql> mysql> select * from test_user where address like 'Hang%';
+----+--------+-------------+----------+
| id | name   | mobile      | address  |
+----+--------+-------------+----------+
|  3 | python | 18856565858 | Hangzhou |
|  4 | java   | 17756565858 | Hangzhou |
|  5 | php    | 15556565858 | Hangzhou |
|  6 | c#     | 17748484142 | Hangzhou |
+----+--------+-------------+----------+
4 rows in set (0.00 sec)
mysql>

查询地址以u结尾的人员信息

mysql> select * from test_user where address like '%u';
+----+--------+-------------+----------+
| id | name   | mobile      | address  |
+----+--------+-------------+----------+
|  3 | python | 18856565858 | Hangzhou |
|  4 | java   | 17756565858 | Hangzhou |
|  5 | php    | 15556565858 | Hangzhou |
|  6 | c#     | 17748484142 | Hangzhou |
+----+--------+-------------+----------+
4 rows in set (0.00 sec)
mysql>

示例2：使用python脚本执行含LIKE的sql语句

查询地址包含z字符的人员信息

import pymysql
 
# 连接数据库
connection = pymysql.connect(host="localhost", user="root", password="123456",
                             database="testing", port=3306, charset='utf8',
                             cursorclass=pymysql.cursors.DictCursor)
 
try:
    with connection:
        with connection.cursor() as cursor:
            sql = """
                SELECT
                    *
                FROM
                    test_user
                WHERE
                    address LIKE '%z%';
            """
            cursor.execute(sql)
            result = cursor.fetchall()
            for i in result:
                print(i)
 
except pymysql.err.MySQLError as _error:
    raise _error

{'id': 3, 'name': 'python', 'mobile': '18856565858', 'address': 'Hangzhou'}
{'id': 4, 'name': 'java', 'mobile': '17756565858', 'address': 'Hangzhou'}
{'id': 5, 'name': 'php', 'mobile': '15556565858', 'address': 'Hangzhou'}
{'id': 6, 'name': 'c#', 'mobile': '17748484142', 'address': 'Hangzhou'}
 
Process finished with exit code 0

查询地址不包含z字符的人员信息

try:
    with connection:
        with connection.cursor() as cursor:
            sql = """
                SELECT
                    *
                FROM
                    test_user
                WHERE
                    address NOT LIKE '%z%';
            """
            cursor.execute(sql)
            result = cursor.fetchall()
            for i in result:
                print(i)
 
except pymysql.err.MySQLError as _error:
    raise _error

{'id': 1, 'name': '张三三', 'mobile': '17748484141', 'address': '浙江杭州'}
{'id': 9, 'name': '111', 'mobile': '18847474549', 'address': '浙江杭州'}
 
Process finished with exit code 0

至此，使用LIKE操作符查询完毕...

知识点扩展：python中的mysql数据库like模糊查询

%在python中是个特殊的符号，如%s，%d分别代表了字符串占位符和数字占位符。

大家知道，mysql的模糊查询也需要用到%。

所以，可以先把需要查的字符串抽出来，再以参数方式传入。

args = '%'+subtitle+'%'
sqlQueryTitle="select count(*) from tbl_peng_article where title like '%s'"%args

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