ad949c2f65
I tested hex in a 1000w times for loop with random numbers， old hex avg time cost is 4.92 s，optimize hex avg time cost is 0.46 s which faster nearly 10x.
64 lines
1.5 KiB
Markdown
64 lines
1.5 KiB
Markdown
---
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{
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"title": "unhex",
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"language": "zh-CN"
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}
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---
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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# unhex
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## description
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### Syntax
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`VARCHAR unhex(VARCHAR str)`
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输入字符串，如果字符串长度为0或者为奇数，返回空串；
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如果字符串中包含`[0-9]、[a-z]、[A-Z]`之外的字符，返回空串；
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其他情况每两个字符为一组转化为16进制后的字符，然后拼接成字符串输出
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## example
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```
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mysql> select unhex('@');
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+------------+
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| unhex('@') |
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+------------+
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| |
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+------------+
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mysql> select unhex('41');
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+-------------+
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| unhex('41') |
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+-------------+
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| A |
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+-------------+
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mysql> select unhex('4142');
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+---------------+
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| unhex('4142') |
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+---------------+
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| AB |
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+---------------+
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```
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## keyword
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UNHEX
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