select

问题 I will have multiple clients entering data into a database and I must ensure that the transactions do not get intermingled. I read in the documentation that START TRANSACTION and SELECT ... FOR UPDATE locks each row that it reads: A SELECT ... FOR UPDATE reads the latest available data, setting exclusive locks on each row it reads. Thus, it sets the same locks a searched SQL UPDATE would set on the rows. See https://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html So I logged in one

问题 Im using this: SELECT * WHERE id=MAX(id) FROM history; But my query is empty. I have also tried this (This one works): SELECT MAX(id) AS max_id FROM history; But obviusly my query only contains the max_id key. What am I doing wrong with the first one? 回答1: You need to add another level of select for the MAX , like this: SELECT * WHERE id=(SELECT MAX(id) from history) FROM history; A better approach would be to order by id in descending order, and limit the output to a single row: SELECT *

问题 Below is my query. SELECT n.`name`,n.`customer_id`,m.`msn`, m.kwh, m.kwh - LAG(m.kwh) OVER(PARTITION BY n.`customer_id` ORDER BY m.`data_date_time`) AS kwh_diff FROM mdc_node n INNER JOIN `mdc_meters_data` m ON n.`customer_id` = m.`cust_id` WHERE n.`lft` = 5 AND n.`icon` NOT IN ('folder') AND m.`data_date_time` BETWEEN NOW() - INTERVAL 30 DAY AND NOW() Which gives me below result I want to sum up the kwh_diff and to show only one-row record not multiple like below name customer_id msn sum_kwh

问题 I have a table containing Boolean values for travel modes, which looks like: SELECT * FROM survey; +----+-------+-------+-------+-------+ | id | bike | car | bus | metro | +----+-------+-------+-------+-------+ | 49 | false | false | true | false | | 51 | false | true | false | false | | 52 | false | false | false | true | | 53 | false | true | false | false | +----+-------+-------+-------+-------+ Then I want select only the modes for which the value is true , so that the end result is: +---

问题 So my table has 2 columns: hour and customerID. Every customer will have 2 rows, one corresponding to hour that he/she came into the store, and one corresponding to hour that he/she left the store. With this data, I want to create a table that has every hour that a customer has been in the store. For example, a customer X entered the store at 1PM and left at 5PM, so there would be 5 rows (1 for each hour) like the screenshot below. Here's my attempt that's now: select hour ,first_value

问题 I have a user interface where a user can move multiple options between two select lists. It looks just like this mock up here: You select one or multiple items then press the arrow button and it moves them into the other list. The problem is I have a sort function to resort the options after they've been moved and really weird stuff is happening. When you first move options from the left to the right it works fine. If you move another item from the left to right it overwrites what is already

问题 I try to handle a multiple form select option , in ReactJS. I have tried to be inspire of javascript classic code to handle that, but I fail. My code just don't send me the values selected. How handle that ? Here my code : class ChooseYourCharacter extends React.Component { constructor(props) { super(props); this.state = {value: 'coconut'}; this.handleChange = this.handleChange.bind(this); this.handleSubmit = this.handleSubmit.bind(this); } handleChange(event) { this.setState({value: event

问题 I'm really curious to know if there is a way to create a multiple select option in a dropdown with material design lite, I've search everywhere and I've only been able to implement it using materializecss, need to know if its possible with material design lite 回答1: It's 13/05/2020. Still nothing for MDL. Depending on what you use, slim select could be useful. I ended up re-designing to exclude the multiselect dropdown myself. 来源： https://stackoverflow.com/questions/47524544/multiple-select

问题 I've the following query: SELECT tn.Date, b1.Name DrBook, b2.Name CrBook, c1.Name DrControl, c2.Name CrControl, l1.Name DrLedger, l2.Name CrLedger, s1.Name DrSubLedger, s2.Name CrSubLedger, p1.Name DrParty, p2.Name CrParty, m1.Name DrMember, m2.Name CrMember, tn.Amount, tn.Narration FROM Transactions tn LEFT JOIN Books b1 ON b1.Id = tn.DrBook LEFT JOIN Books b2 ON b2.Id = tn.CrBook LEFT JOIN ControlLedgers c1 ON c1.Id = tn.DrControl LEFT JOIN ControlLedgers c2 ON c2.Id = tn.CrControl LEFT

问题 i want to learn that when i select a value from select input how can i change the value of checkbox. <input type="checkbox" name="id" value="" id="mycheckbox1"> <select name="cat-1" id="myselectbox1"> <option value="">Choose</option> <option value="100">Value1</option> <option value="200">Value2</option> </select> 回答1: Why would you want to? Anyway: window.addEventListener("load", function() { // on page load document.getElementById("myselectbox1").addEventListener("change", function() {