if(code.length != codeLength){ createCode(); }

这也是一段 JavaScript 代码，它包含在一个函数中。这个函数的作用是生成一个长度为 codeLength 的随机字符串，并将其存储在变量 code 中。如果生成的字符串的长度不等于 codeLength，则递归调用函数来重新生成字符串。这段代码通常用于生成验证码等场景，以确保生成的字符串的长度是固定的。

相关问题

帮我优化一下这个sql select e.id, e.mobile, e.encoded, CASE e.is_echo WHEN 1 THEN '已回传' else '未回传' END AS isEcho , e.order_no AS orderNo, e.pay_amount AS payAmount, e.operator_id AS operatorId, e.operator_name AS operatorName, e.operator_time AS operatorTime, e.remarks AS remarks, e.`status`, CASE p.pay_status WHEN 1 THEN '支付成功' WHEN 2 THEN '支付失败' END AS payStatus , CASE e.status WHEN 1 THEN '待支付' WHEN 2 THEN '已支付' WHEN 3 THEN '已退款' WHEN 4 THEN '订单关闭' WHEN 5 THEN '退款中' WHEN 6 THEN '退款关闭' END AS statusName, e.create_time AS createTime, u.id AS userId, p.pay_channel AS payChannel, CASE p.pay_channel WHEN 1 THEN '支付宝' WHEN 2 THEN '微信' END AS payChannelName , p.out_trade_no AS outTradeNo, e.third_party_channel AS thirdPartyChannel, info.return_amount AS returnAmount, info.return_phone AS returnPhone, info.return_name AS returnName from equity.equity_order_info e left join equity.user_info u on e.mobile = u.user_photo LEFT JOIN ( SELECT * FROM equity.pay_message GROUP BY order_no ) AS p ON p.order_no = e.order_no left join equity.refund_info AS info ON info.order_no=e.order_no <where> <if test="mobile != null and mobile != ''">and e.mobile = #{mobile}</if> <if test="orderNo != null and orderNo != ''">and e.order_no = #{orderNo}</if> <if test="payAmount != null ">and e.pay_amount = #{payAmount}</if> <if test="thirdPartyChannel != null and thirdPartyChannel != ''">and e.third_party_channel = #{thirdPartyChannel} </if> <if test="outTradeNo != null and outTradeNo != ''">and p.out_trade_no = #{outTradeNo} </if> <if test="startTime != null and startTime != '' and endTime != null and endTime != ''"> and DATE_FORMAT(e.create_time,'%Y-%m-%d') BETWEEN DATE_FORMAT(#{startTime},'%Y-%m-%d') AND DATE_FORMAT(#{endTime},'%Y-%m-%d') </if> <if test="status != null and status > 0">and e.status = #{status}</if> <if test="userId != null ">and u.id = #{userId}</if> </where> ORDER BY e.create_time DESC

#{mobile}</if>
<if test="startTime != null">and e.create_time &gt;= #{startTime}</if>
<if test="endTime != null">and e.create_time &lt;= #{endTime}</if>
<if test="status != null">and e.`status` = #{status}</if>
<if test="payStatus != null">and p.pay_status = #{payStatus}</if>
<if test="payChannel != null">and p.pay_channel = #{payChannel}</if>
</where>
ORDER BY e.create_time DESC, e.id DESC
LIMIT #{start},#{length}</code></pre>

优化建议：
1. 尽可能避免使用SELECT *
2. group by 关键字比其他的聚合函数效率低，尽量避免使用
3. 减少使用CASE WHEN，可以使用join来加快速度
4. 尽量减少WHERE子句中的嵌套IF条件，可以使用join来加快速度
5. 为需要检索的列创建索引，如E.mobile、P.pay_channel、E.`status`等

code = ""; //验证码长度为4.从数字和字母当中随机进行选择 var codeLength = 4; var selectChar = new Array(1,2,3,4,5,6,7,8,9,'a','b','c','d','e','f','g','h','j','k','l','m','n','p','q','r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z'); //在selectChar中随机选择4个字符作为验证码，采用的是递归方法一位位创建 for(var i=0;i<codeLength;i++) { var charIndex = Math.floor(Math.random()*60); code +=selectChar[charIndex]; } if(code.length != codeLength){ createCode(); } //调用显示模块 showCheck(code);

这是一段用于生成验证码的 JavaScript 代码。首先，它将变量 code 的值设为空字符串，并将验证码长度设置为 4。然后，它创建了一个包含数字和字母的数组 selectChar，这个数组包含了所有可能用于生成验证码的字符。接下来，使用 for 循环从 selectChar 数组中随机选择 4 个字符，通过递归方法一位位创建验证码。最后，如果生成的验证码的长度不等于 4，则会再次调用 createCode 函数来重新生成验证码。最后，它调用 showCheck 函数来显示生成的验证码。通常，验证码用于防止机器人恶意破解等场景。