Open jackieli123723 opened 7 years ago
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<h1 >MySQL获取行数</h1> <p>¥ 我要打赏 <a href="/mysql/">MySQL教程</a> 作者:初生不惑 评论:0 条 <a href="//shang.qq.com/wpa/qunwpa?idkey=c7c79783f2da15e2244981dfbd17c18b6a71b8bc5d018e248d59919bd614e18f" title="直接点击加群">IT技术QQ群:227270512</a></p> <p><a href="https://jq.qq.com/?_wv=1027&k=46RCS7y" title="java直播学习群QQ群:172393525"> <img src="http://www.yiibai.com/static/images/adv/javaweb730x90.jpg" alt="java直播学习群QQ群:172393525" title="java直播学习群QQ群:172393525"></a></p> <p>在本教程中,您将学习在数据库中获取MySQL行计数的各种方法。</p> <h2 id="-mysql-">获取单个表的MySQL行计数</h2> <p>要获取单个表的行计数,可以在<a href="http://www.yiibai.com/mysql/select-statement-query-data.html" title="SELECT">SELECT</a>语句中使用<a href="http://www.yiibai.com/mysql/count.html" title="COUNT(*)">COUNT(*)</a>,如下所示:</p> <pre><code>SELECT COUNT(*) FROM table_name; </code></pre><p>例如,要获取<a href="http://www.yiibai.com/mysql/sample-database.html" title="示例数据库(yiibaidb)">示例数据库(yiibaidb)</a>中的<code>customers</code>表中的行数,可以使用以下语句:</p> <pre><code>SELECT COUNT(*) FROM customers; </code></pre><p>执行上面查询语句,得到以下结果 -</p> <pre><code>+----------+ | COUNT(*) | +----------+ | 122 | +----------+ 1 row in set (0.01 sec) </code></pre><p><strong>获取MySQL两个或多个表的行计数</strong></p> <p>要获取多个表的行数,可以使用<a href="http://www.yiibai.com/sql-union-mysql.html" title="UNION">UNION</a>运算符组合每个<code>SELECT</code>语句返回的结果集。</p> <p>例如,要在单个查询中获取<code>customers</code>和<code>orders</code>表的行数,请使用以下语句。</p> <pre><code>SELECT 'customers' tablename, COUNT(*) rows FROM customers UNION SELECT 'orders' tablename, COUNT(*) rows FROM orders; </code></pre><p><strong>获取特定数据库中所有表的MySQL行计数</strong></p> <p>要获取行计数特定数据库中的所有表,例如<code>yiibaidb</code>数据,请按照以下步骤:</p> <ul> <li>首先,获取数据库中的所有表名</li> <li>第二步,构造一个SQL语句,其中包含由<code>UNION</code>分隔的所有表的所有<code>SELECT COUNT(*)FROM table_name</code>语句。</li> <li>第三步,使用<a href="http://www.yiibai.com/mysql/prepared-statement.html" title="准备语句">准备语句</a>执行SQL语句。</li> </ul> <p><strong>第一步</strong>,要获取数据库的所有表名,请从<code>information_schema</code>数据库中查询如下:</p> <pre><code>SELECT table_name FROM information_schema.tables WHERE table_schema = 'yiibaidb' AND table_type = 'BASE TABLE'; </code></pre><p>执行上面查询,得到以下结果 -</p> <pre><code>+--------------+ | TABLE_NAME | +--------------+ | customers | | employees | | offices | | orderdetails | | orders | | payments | | productlines | | products | +--------------+ 8 rows in set (0.02 sec) </code></pre><p><strong>第二步</strong>,构造SQL语句,我们使用<a href="http://www.yiibai.com/mysql/group_concat.html" title="GROUP_CONCAT">GROUP_CONCAT</a>和<a href="http://www.yiibai.com/sql-concat-in-mysql.html" title="CONCAT">CONCAT</a>函数如下:</p> <pre><code>SELECT CONCAT(GROUP_CONCAT(CONCAT('SELECT '', table_name, '' table_name,COUNT(*) rows FROM ', table_name) SEPARATOR ' UNION '), ' ORDER BY table_name') INTO @sql FROM table_list; </code></pre><p>在此查询中,<code>table_list</code>是第一步中查询结果的表名列表。</p> <p>以下查询使用第一个查询作为派生表,并以字符串形式返回SQL语句。</p> <pre><code>SELECT CONCAT(GROUP_CONCAT(CONCAT('SELECT '', table_name, '' table_name,COUNT(*) rows FROM ', table_name) SEPARATOR ' UNION '), ' ORDER BY table_name') INTO @sql FROM (SELECT table_name FROM information_schema.tables WHERE table_schema = 'yiibaidb' AND table_type = 'BASE TABLE') table_list; </code></pre><p>如果您使用<em>MySQL 8.0+</em>,则可以使用<a href="http://www.yiibai.com/mysql/cte.html" title="MySQL CTE">MySQL CTE</a>(通用表表达式)而不是派生表:</p> <pre><code>WITH table_list AS ( SELECT table_name FROM information_schema.tables WHERE table_schema = 'yiibaidb' AND table_type = 'BASE TABLE' ) SELECT CONCAT( GROUP_CONCAT(CONCAT("SELECT '",table_name,"' table_name,COUNT(*) rows FROM ",table_name) SEPARATOR " UNION "), ' ORDER BY table_name' ) INTO @sql FROM table_list; </code></pre><p><strong>第三步</strong>,使用<a href="http://www.yiibai.com/mysql/prepared-statement.html" title="prepare语句">prepare语句</a>执行<code>@sql</code>语句,如下所示:</p> <pre><code>USE yiibaidb; PREPARE s FROM @sql; EXECUTE s; DEALLOCATE PREPARE s; </code></pre><p>执行上面查询统计语句,得到以下结果 -</p> <pre><code>+--------------+------+ | table_name | rows | +--------------+------+ | customers | 122 | | departments | 0 | | employees | 23 | | items | 9 | | offices | 7 | | orderdetails | 2998 | | orders | 327 | | payments | 273 | | productlines | 7 | | products | 110 | | tasks | 0 | | tokens | 1 | +--------------+------+ 12 rows in set </code></pre><p><strong>使用一个查询获取数据库中所有表的MySQL行计数</strong></p> <p>获取数据库中所有表的行计数的快速方法是直接从<code>information_schema</code>数据库中查询数据:</p> <pre><code>SELECT table_name, table_rows FROM information_schema.tables WHERE table_schema = 'yiibaidb' ORDER BY table_rows desc; </code></pre><p>执行上面查询,得到以下结果 -</p> <pre><code>mysql> SELECT table_name, table_rows FROM information_schema.tables WHERE table_schema = 'yiibaidb' ORDER BY table_rows desc; +--------------+------------+ | table_name | table_rows | +--------------+------------+ | orderdetails | 2731 | | orders | 326 | | payments | 256 | | customers | 122 | | products | 110 | | employees | 23 | | items | 9 | | productlines | 7 | | offices | 7 | | tokens | 0 | | tasks | 0 | | departments | 0 | +--------------+------------+ 12 rows in set
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vue 高亮html富文本
主要是做爬虫过滤html代码后放入自己项目来使用记录哈
配合使用vue2-editor
富文本源码(HTML)
高亮highlight.js(可局部组件引用或者全局引用,可修改highlight_code-css样式)
vue-main.js